Original data and independent reporting for the HVAC trade

Category: Homeowners

Cost guides, repair versus replace, and how to read a quote.

  • What an HVAC Warranty Actually Covers, and What It Does Not

    What an HVAC Warranty Actually Covers, and What It Does Not

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    An HVAC warranty usually covers the part and not the labour to fit it, and registration is often required within a set window after installation or the term drops. Those two details decide most of what a warranty is actually worth.

    Manufacturer parts warranty, contractor labour warranty and a third-party home warranty are three different products. They get discussed as one thing and they fail in different ways.

    The three things called a warranty

    Type Who provides it Typically covers Typically excludes
    Manufacturer parts warranty Equipment maker The failed component Labour, refrigerant, diagnostics, travel
    Contractor labour warranty The installing company Labour for a defined period Parts, and it ends if the company does
    Home warranty or service contract Third party Varies by contract Varies by contract, often pre-existing faults

    A parts warranty on a compressor sounds substantial until you price the labour, the refrigerant recovery and the recharge that fitting it requires, none of which the parts warranty pays.

    What most often voids or shortens coverage

    1. Not registering. Many manufacturers require registration within a window after installation, and the unregistered term is shorter.
    2. Unlicensed or DIY installation. Coverage commonly requires installation by a qualified contractor.
    3. No documented maintenance. Some terms require evidence of servicing, which is a contractual requirement rather than a federal one. See what the evidence says about intervals.
    4. Non-original parts. Substituting components can void remaining coverage.
    5. Transfer on sale. Some warranties transfer to a new owner, some do not, and some require a fee and a form within a window.
    The question that reveals the real value

    Ask what a covered compressor failure would cost you out of pocket. If the answer includes diagnostic time, labour, refrigerant recovery and recharge, you have learned what the warranty does not cover, which is the part that matters. On an R-410A system the refrigerant line of that answer gets less comfortable each year under the phasedown schedule.

    Frequently asked questions

    Does an HVAC warranty cover labour?

    Usually not. A manufacturer parts warranty typically covers the failed component only, leaving diagnostic time, labour, refrigerant recovery and recharge to the owner. Labour coverage normally comes separately from the installing contractor, for a shorter defined period, and it ends if that company ceases trading.

    Do I need to register my HVAC warranty?

    Often yes, and within a limited window after installation. Many manufacturers offer a longer term to registered owners and a shorter default term to everyone else. Registration is one of the most common reasons a warranty turns out to be shorter than the owner believed.

    What voids an HVAC warranty?

    Common causes are failing to register in time, installation by an unqualified party, absence of documented maintenance where the terms require it, and substituting non-original parts. Transfer rules on sale also vary, with some warranties requiring a fee and a form within a window.

    Is a home warranty worth it for HVAC?

    That depends entirely on the contract, and no federal source measures the value of these products. Read what is excluded rather than what is covered, check how pre-existing conditions are defined, and confirm who chooses the contractor and what the payout limits are per claim and per year.

    Methodology and limitations

    This page describes contract structures in general terms. Warranty terms are private contracts and vary by manufacturer, contractor and provider.

    • We name no manufacturers or warranty providers and rate none.
    • No federal source measures warranty claim rates or the value of service contracts.
    • Nothing here is legal advice. Your specific terms govern, and consumer protection rules vary by state.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • HVAC Financing: What to Establish Before You Sign

    HVAC Financing: What to Establish Before You Sign

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    HVAC financing became a bigger part of the decision after the federal 25C tax credit expired for anything placed in service after December 31, 2025, removing up to $2,000 from a qualifying heat pump job.

    Equipment producer prices are also up 60% since 2019. A larger bill with no federal credit against it is why payment structure now comes up earlier in the conversation than it used to.

    We do not compare lenders or rate offers. What follows is what to establish before signing, and which numbers are documented.

    What changed on the incentive side

    Factor 2025 2026
    Federal 25C credit, qualifying heat pump Up to $2,000 $0
    What controls eligibility Placed in service by Dec 31, 2025 Not available
    State and utility rebates Unaffected Unaffected
    Equipment producer prices vs 2019 Up 60%, July 2026 the series high

    Details of the credit expiry are in what the 25C change costs, and the price trend in our price index analysis.

    What to establish before signing

    1. The total amount repayable, not the monthly figure. Two offers with the same monthly payment over different terms are not the same offer.
    2. The annual percentage rate, and whether any promotional rate expires into a higher one.
    3. Whether deferred interest applies. Some promotional structures charge interest retrospectively from day one if the balance is not cleared within the promotional window.
    4. Any dealer fee built into the price. A financed price and a cash price are sometimes different numbers for the same job.
    5. Whether the obligation attaches to you or the property. Some programmes secure the debt against the home, which affects sale and refinancing.
    6. Early repayment terms, including whether paying early reduces total interest.
    Check rebates before financing

    State and utility rebate programmes were not affected by the federal credit expiring, and they vary by utility rather than by state, so a neighbouring town can have a materially different offer. Establishing what is available reduces the amount financed, which changes every other number in the deal. Confirm with the specific utility rather than assuming.

    Frequently asked questions

    Is there still a tax credit for HVAC in 2026?

    Not federally. The Section 25C Energy Efficient Home Improvement Credit applied to property placed in service before December 31, 2025, and installation date controls rather than purchase date. State and utility rebate programmes are separate and were unaffected by that expiry.

    What should I check in an HVAC financing offer?

    The total amount repayable rather than the monthly payment, the annual percentage rate and whether a promotional rate expires, whether deferred interest applies retrospectively, any dealer fee built into the financed price, whether the obligation attaches to the property, and early repayment terms.

    What is deferred interest?

    A promotional structure where interest accrues from the start but is only charged if the balance is not cleared within the promotional period. Clearing it in time costs nothing; missing the window by a small amount can trigger interest calculated back to day one on the original balance.

    Why did HVAC costs rise so much?

    Equipment producer prices are up about 60% since 2019, roughly twice general consumer inflation, with August 2026 the highest reading in the BLS series. The federal 25C credit worth up to $2,000 also expired for installations after December 31, 2025.

    Methodology and limitations

    Credit terms are from the IRS. Equipment price movement is BLS series PCU333415333415 indexed to its 2019 annual average.

    • We name no lenders and compare no rate offers.
    • Nothing here is financial advice. Terms vary by provider, product and jurisdiction, and consumer credit rules differ by state.
    • We publish no installed costs, as no federal series measures them.

    Sources

    1. Internal Revenue Service, Energy Efficient Home Improvement Credit.
    2. US Bureau of Labor Statistics, Producer Price Index series PCU333415333415.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • UV Lights and Air Purifiers: The Questions Marketing Skips

    UV Lights and Air Purifiers: The Questions Marketing Skips

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    In-duct UV lights and add-on air cleaners are sold with performance claims that no federal agency verifies, and the numbers quoted come from manufacturer testing rather than an independent standard.

    That does not make them useless. It means the burden is on the seller to say what was tested, under what conditions, and by whom, and most marketing does not.

    Two different products get sold together and they do different things. Filtration removes particles from circulating air. UV is intended to act on biological growth. Neither exchanges air with outdoors, which is the thing people often actually want.

    What each product category actually does

    Product Intended action What it does not do
    Coil UV light Irradiates the evaporator coil surface to limit growth on it Does not treat air passing at duct velocity
    In-duct air UV Irradiates air in the duct stream Effectiveness depends heavily on exposure time and dose
    Media air cleaner Higher surface area filtration Does not exchange air, and adds pressure drop
    Electronic air cleaner Charges and collects particles Requires cleaning to keep working
    Ventilator (ERV/HRV) Actually exchanges indoor and outdoor air Not a filtration product

    If the goal is fresh air rather than cleaner recirculated air, none of the first four addresses it. See what ventilation actually means.

    The questions that separate a product from a claim

    1. What was tested, the coil or the airstream? A lamp sized to keep a coil clean is not the same as one intended to treat moving air.
    2. At what airflow? UV dose depends on exposure time. A result at low velocity does not transfer to a system moving air at duct speed.
    3. Tested by whom, against what standard? Manufacturer laboratory results are not independent verification.
    4. What is the pressure drop? Any added filtration raises static pressure, which reduces airflow. See why filter choice affects airflow.
    5. What is the maintenance cycle? Lamps lose output over time and cells need cleaning; an unmaintained device is decorative.
    The one thing UV reliably addresses

    A coil that stays damp between cycles grows biological material, which is the usual source of musty odour. A lamp aimed at that coil targets a real and specific problem. Whether the same lamp does anything useful to air moving past it at duct velocity is a separate question with a separate answer. See what musty smells actually indicate.

    Frequently asked questions

    Do UV lights in HVAC systems work?

    A lamp aimed at the evaporator coil addresses growth on that coil, which is a real and specific problem and the usual source of musty odour. Claims about treating air moving through the duct are a separate question, because effectiveness depends on dose and exposure time at duct velocity. No federal agency verifies these performance claims.

    Are air purifiers worth adding to HVAC?

    It depends what problem you are solving. Added filtration removes more particles from recirculating air and also increases pressure drop, reducing airflow. Neither filtration nor UV exchanges indoor air with outdoor air, so if the concern is fresh air, a ventilator rather than a purifier is the relevant product.

    Why do performance claims vary so much between products?

    Because there is no single federal standard verifying them. Figures come from manufacturer testing under conditions the marketing rarely states, and results depend heavily on airflow, dose, chamber size and what was actually measured. Ask what was tested, at what airflow, and by whom.

    Will an air cleaner reduce my energy use?

    Not directly, and denser filtration usually increases blower energy by raising static pressure. A clean coil does help the system run as designed, which is the mechanism behind coil-focused UV, but that is a maintenance benefit rather than an efficiency product.

    Methodology and limitations

    This page describes product categories and the questions that distinguish tested performance from marketing. We publish no efficacy figures, because no federal source verifies them and manufacturer results are not comparable across products.

    • No product is named, recommended or criticised. We do not review equipment.
    • No efficacy percentage is quoted for any device.
    • Health claims are outside our scope. Nothing here is medical or air quality advice.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • Your AC Does Not Need a Recharge. It Has a Leak.

    Your AC Does Not Need a Recharge. It Has a Leak.

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    Air conditioners do not consume refrigerant, so a system that needs recharging has a leak. Recharging without finding that leak restores cooling temporarily while the refrigerant escapes again.

    That matters more than it used to. Under the federal HFC phasedown, production allowances drop from 60% of baseline to 30% on January 1, 2029, so refrigerant for older systems gets scarcer on a published timetable.

    The phrase “needs a recharge” describes a symptom as though it were routine maintenance. It is not routine, and treating it that way is how a small leak becomes an annual bill.

    Why a sealed system should never need topping up

    Refrigerant circulates in a closed loop, changing state between liquid and vapour. Nothing in normal operation consumes it. If the charge is low, it left through a physical opening: a failed joint, a corroded coil, a service valve, or a crack.

    What you are told What it means
    “It just needs a recharge” The system has a leak that has not been located
    “It is low on Freon” Same, with a brand name that identifies nothing. See why Freon is not a type
    “They all lose a bit over time” Not true of a sealed circuit in normal operation
    “We topped it up last year too” An unrepaired leak, now with two charges vented

    What to ask before authorising a recharge

    1. Where is the leak? A leak search is a distinct diagnostic step, not something inferred from low pressure.
    2. How much refrigerant is going in? A large charge on a residential system indicates a significant loss.
    3. What refrigerant is it? R-22 has not been produced since January 1, 2020, so it comes from reclaimed stock. See what remains of R-22.
    4. What happens when it recurs? Get the plan in writing, including whether the repair is worth doing against replacement.
    5. Is the repair economic? A leaking evaporator coil on an older R-410A system often decides the replace-or-repair question by itself.
    The regulatory position

    Venting refrigerant is prohibited under 40 CFR part 82, and technicians handling it must hold EPA Section 608 certification. Notably, the 2026 leak repair rules at 40 CFR 84.106 apply at 15 or more pounds of charge and explicitly exclude residential equipment, so there is no federal record-keeping obligation on a home system. That is a regulatory exemption, not an engineering one. See who those rules actually cover.

    Frequently asked questions

    Does an air conditioner need refrigerant recharged regularly?

    No. Refrigerant circulates in a sealed loop and is not consumed by normal operation, so a system that is low has lost it through a leak. Regular topping up is not maintenance, it is an unrepaired fault being managed rather than fixed.

    How much does an AC recharge cost?

    No federal series tracks residential refrigerant or repair pricing, so any figure quoted is a vendor estimate rather than measured data. What is documented is that HFC production allowances drop from 60% of baseline to 30% on January 1, 2029, which constrains supply for older systems over time.

    Why does my AC keep losing refrigerant?

    Because the leak was never located and repaired. Common sites are the evaporator coil, brazed joints, service valves and line set connections. Each recharge restores cooling until enough has escaped again, and each one vents a controlled substance into the atmosphere.

    Is it worth repairing a refrigerant leak?

    It depends where the leak is and what the system is worth. An accessible joint is usually a straightforward repair. A leaking evaporator coil on an older R-410A system often decides replacement instead, because the part, the labour and the recovery and recharge all land together.

    Methodology and limitations

    Regulatory positions are from 40 CFR part 82 for venting and certification, 40 CFR 84.106 for leak repair applicability, and 40 CFR 84.7 for the phasedown schedule.

    • We publish no recharge or repair prices, as no federal series measures them.
    • Leak location and repair economics are system specific.
    • Refrigerant work requires EPA Section 608 certification and is not owner serviceable.

    Sources

    1. US Environmental Protection Agency, 40 CFR part 82 subpart F; 40 CFR 84.106; 40 CFR 84.7.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • What Air Conditioning Costs to Run, and Why No National Figure Works

    What Air Conditioning Costs to Run, and Why No National Figure Works

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    There is no useful national figure for what air conditioning costs to run, because residential electricity prices vary about 4-fold across US states. The US average was 18.34 cents per kilowatt hour in June 2026, but Nevada was 13.11 and Hawaii was 52.72.

    Running cost is your rate multiplied by your consumption. Anyone quoting a dollars-per-month figure without knowing your rate is guessing at the larger of the two variables.

    The calculation itself is simple. What makes published estimates unreliable is that they fix a rate you almost certainly do not pay.

    What electricity actually costs, by state

    State June 2026 (cents/kWh) June 2025 Change
    US average 18.34 17.47 +5.0%
    Hawaii 52.72 40.96 +28.7%
    California 34.74 33.59 +3.4%
    Massachusetts 29.61 30.33 -2.4%
    New York 29.49 26.55 +11.1%
    Illinois 19.89 18.29 +8.7%
    Ohio 19.19 17.50 +9.7%
    Georgia 16.36 15.96 +2.5%
    Texas 15.94 15.26 +4.5%
    Florida 15.10 15.35 -1.6%
    Louisiana 13.49 12.74 +5.9%
    Nevada 13.11 12.26 +6.9%

    Residential prices rose 5.0% nationally against June 2025, but the change was far from uniform: some states rose by double digits while others fell.

    How to work out your own number

    1. Find your rate. Divide the total electricity charge on your bill by the kilowatt hours used. Do not use the headline supply rate, which excludes delivery charges that are often a third or more of the bill.
    2. Find the equipment draw. The data plate on the outdoor unit states electrical characteristics. A technician can measure actual running amps, which is more useful than nameplate.
    3. Estimate run hours. This is the variable nobody else can supply. It depends on climate, insulation, sizing and thermostat behaviour.
    4. Multiply. Kilowatts multiplied by run hours multiplied by your rate.

    The third step is why published averages fail. Two identical houses in the same city with different insulation and different thermostat habits can differ by a factor of two in run hours.

    Efficiency ratings compare equipment, not bills

    SEER2 describes how much cooling a machine delivers per unit of electricity under standard test conditions. It does not tell you what your bill will be, because it says nothing about your rate, your climate or your run hours. A high SEER2 system in Hawaii can cost more to run than a low SEER2 system in Nevada. See our guide to SEER2 minimums.

    What actually moves the number

    Run time is the lever, and most of what determines it sits outside the equipment. A correctly sized system in a well sealed house with sound ductwork runs fewer hours than an oversized system in a leaky one, regardless of the rating on either.

    Our guides on sizing and ductwork and airflow cover the two that most often go wrong.

    Frequently asked questions

    How much does it cost to run air conditioning per month?

    There is no reliable national figure, because residential electricity rates vary roughly 4-fold between states. The US average was 18.34 cents per kilowatt hour in June 2026, against 13.11 in Nevada and 52.72 in Hawaii. Your cost is your rate multiplied by your consumption, and both are local.

    What is the average electricity price in the US?

    18.34 cents per kilowatt hour for residential customers in June 2026, up 5.0% from 17.47 cents in June 2025, per the EIA Electric Power Monthly. State averages ranged from 13.11 cents in Nevada to 52.72 cents in Hawaii.

    Does a higher SEER2 rating lower my bill?

    It lowers the electricity needed per unit of cooling under standard test conditions, but your bill depends on your rate, your climate and your run hours as well. A high efficiency system in an expensive electricity market can cost more to run than a lower efficiency one in a cheap market.

    How do I calculate my own running cost?

    Divide the total electricity charge on your bill by kilowatt hours used to get your true rate including delivery, find the equipment’s electrical draw from the data plate or a measured reading, estimate run hours for your climate and house, then multiply the three. Run hours is the variable published estimates cannot know.

    Methodology and limitations

    Electricity prices are the US Energy Information Administration Electric Power Monthly, Table 5.6.A, average price of electricity to ultimate customers by end-use sector and state, residential column, June 2026 and June 2025, released August 26, 2026.

    • These are state averages. Utility territories within a state differ, and time-of-use tariffs differ again.
    • We publish no dollars-per-month running cost, because run hours cannot be known from published data.
    • Data plate figures describe rated draw, not measured operating draw.

    Sources

    1. US Energy Information Administration, Electric Power Monthly, Table 5.6.A, June 2026, released August 26, 2026.
    2. US Department of Energy, 10 CFR 430.32, efficiency standards.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • AC Running but Not Cooling: Work It Out in Three Steps

    AC Running but Not Cooling: Work It Out in Three Steps

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    Before listing causes, split the symptom: is the air not cold, or is there barely any air at all? That single question separates a refrigerant or compressor problem from an airflow problem, and it changes what you check first.

    Most published lists give you seven possible causes in no particular order. This one routes by what you can observe, which is what you actually have to work with.

    Start at the vents with your hand. Everything below follows from what you feel there.

    Step 1: air is moving but it is not cold

    The blower is working, so the problem is on the refrigeration side or the equipment is not being asked to cool.

    1. Check the thermostat is set to cool and below room temperature. This is not condescension; it is the most common non-fault.
    2. Check the outdoor unit is running. If the indoor fan runs and the outdoor unit is silent, look at the breaker and the outdoor disconnect.
    3. If the outdoor unit hums but the fan does not turn, that pattern usually points at a capacitor or contactor. See what that noise means.
    4. If everything runs and the air is still warm, the likely causes are low refrigerant charge from a leak or a compressor not pumping. Both need measurement.

    Step 2: barely any air is coming out

    The refrigeration side may be fine. The system cannot deliver what it is producing.

    1. Check the filter. The single most common airflow restriction, and the only one most homeowners can fix.
    2. Check for ice on the indoor coil or refrigerant lines. A frozen coil blocks airflow almost completely. See the two causes of freezing.
    3. Check registers and returns are open and unobstructed, including by furniture and rugs.
    4. If airflow is weak everywhere with a clean filter and no ice, the constraint is usually ductwork or the blower. See why static pressure matters.

    Step 3: it cools, but not enough on hot days

    This is a different failure from the first two and gets misdiagnosed as undersizing.

    Pattern Points toward
    Keeps up in mild weather, falls behind above about 90F Capacity or charge marginal, or condenser coil dirty
    One or two rooms never satisfy, rest are fine Distribution, not capacity
    Cools but the house feels clammy Short cycling, often oversizing
    Runs continuously and never satisfies Charge, airflow, or genuine undersizing

    The clammy case is the one most often answered with a larger system, which makes it worse. See why that happens.

    What is genuinely owner fixable

    The thermostat setting, the filter, the breaker, blocked registers, and debris or vegetation against the outdoor coil. That is the whole list. Everything involving refrigerant, the compressor or electrical components requires certification and measurement, and refrigerant work is regulated under 40 CFR part 82.

    Frequently asked questions

    Why is my AC running but not cooling?

    First establish whether air is moving. If air flows but is not cold, the problem is on the refrigeration side: check the thermostat setting, confirm the outdoor unit is running, then suspect low charge or a compressor fault. If air is barely moving, it is an airflow problem: filter, frozen coil, blocked registers or ductwork.

    What should I check before calling a technician?

    Five things: the thermostat is set to cool and below room temperature, the filter is clean, the breaker and outdoor disconnect are on, registers and returns are unobstructed, and the outdoor unit is clear of vegetation and debris. Everything beyond that requires measurement and, for refrigerant work, EPA certification.

    Why does my AC only struggle on the hottest days?

    A system that keeps up in mild weather but falls behind in extreme heat is usually marginal on capacity or charge, or its outdoor coil is dirty enough to limit heat rejection when it matters most. It can also indicate genuine undersizing, which a load calculation rather than a hot afternoon establishes.

    Does low refrigerant mean I need a recharge?

    It means you have a leak. A sealed refrigerant circuit does not lose charge in normal operation, so adding refrigerant without finding the leak restores cooling temporarily while the loss continues. Ask where the leak is and what the plan is if it recurs.

    Methodology and limitations

    This page organises common causes by observable symptom rather than publishing failure frequencies, because no federal source measures residential HVAC fault rates. Refrigerant handling requirements are from 40 CFR part 82.

    • No probability is claimed for any cause. Symptoms overlap and diagnosis requires measurement.
    • Several causes can be present at once, and one can mask another.
    • Refrigerant and electrical work is not owner serviceable.

    Sources

    1. US Environmental Protection Agency, 40 CFR part 82 subpart F, refrigerant handling and technician certification.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • Single Stage, Two Stage and Variable Speed: What Changes

    Single Stage, Two Stage and Variable Speed: What Changes

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    Single stage equipment is either off or at full output. Two stage runs at roughly partial or full. Variable capacity modulates continuously across a range. The practical difference is run time, and run time is what determines comfort and dehumidification.

    Most hours of the year a house needs far less than design capacity. Equipment that can only deliver 100% satisfies the thermostat quickly and stops, which is the mechanism behind cool but clammy houses.

    The three types compared

    Single stage Two stage Variable capacity
    Output levels Off or full Off, partial, full Continuous modulation
    Typical cycle length Shorter Longer at partial load Longest, often near continuous
    Dehumidification Limited by short cycles Better Best, coil stays engaged
    Temperature swing Largest Moderate Smallest
    Pairs well with zoning Poorly, surplus air when zones close Better Best
    Equipment cost Lowest Middle Highest

    Why run time matters more than capacity

    Dehumidification happens only while the coil is cold and air is moving across it. A system that reaches setpoint in eight minutes and stops has removed very little moisture. One that runs for forty minutes at partial output removes considerably more while holding a steadier temperature.

    That is why adding capacity to a comfort complaint often makes it worse. The intuitive fix increases output when the actual problem is insufficient run time. See why oversizing causes clamminess.

    Staging does not rescue bad sizing

    Two stage and variable capacity equipment tolerate oversizing better than single stage, because they can run below full output. They do not eliminate the problem. An oversized variable capacity system still spends its life at the bottom of its range, and the sizing calculation still governs. See why square-footage sizing fails.

    Where the extra cost is easiest to justify

    1. Humid climates, where dehumidification matters as much as temperature.
    2. Zoned systems, because modulating equipment produces less surplus air when zones close. See how zoning works.
    3. Houses with large temperature swings between rooms or across the day.
    4. Long run seasons, where more operating hours give the efficiency advantage more opportunity to accumulate.

    Where the season is short and the climate dry, the comfort argument is weaker and single stage equipment remains defensible.

    Frequently asked questions

    What is the difference between single stage and two stage HVAC?

    Single stage equipment is either off or running at full output. Two stage adds a partial output level, so it can run longer at lower capacity when the house needs less. Longer run cycles hold temperature more steadily and remove more humidity, because dehumidification only happens while the coil is running.

    Is variable speed HVAC worth it?

    The case is strongest in humid climates, in zoned systems, and where the cooling or heating season is long. Variable capacity modulates continuously, so it runs closer to the actual load and removes more moisture. In short, dry seasons the comfort advantage is smaller and single stage equipment remains defensible.

    Does variable speed fix an oversized system?

    It tolerates oversizing better than single stage because it can run below full output, but it does not eliminate the problem. An oversized variable capacity system spends its life at the bottom of its range. Correct sizing from a load calculation still governs performance.

    Why does longer run time improve comfort?

    Because moisture removal happens only while the coil is cold and air is moving across it. Short cycles satisfy the thermostat on temperature while removing little humidity, which produces a house that is cool and clammy. Longer cycles at lower output hold temperature steadier and dehumidify considerably more.

    Methodology and limitations

    This page describes control behaviour and its consequences. We publish no efficiency or savings figures for staging types, as the result depends on equipment, climate, sizing and ductwork.

    • No percentage saving is claimed for any staging type.
    • Manufacturer implementations of two stage and variable capacity differ.
    • Nothing here is a recommendation for a specific installation.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • HVAC Noises: Which Ones Mean Shut It Off Now

    HVAC Noises: Which Ones Mean Shut It Off Now

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    An HVAC noise is worth acting on when it is new, and worth acting on immediately when it is metallic, electrical or accompanied by the system not starting. Normal operation makes sound; a change in sound is the signal.

    The most common actionable one is a hum or buzz from the outdoor unit with the fan not turning, which typically points at a capacitor or contactor rather than at the compressor.

    What each noise usually indicates

    Noise Where Usually means Act
    Humming or buzzing, fan not turning Outdoor unit Capacitor or contactor not starting the motor Shut off, service call
    Metallic clanking or banging Outdoor unit Loose or contacting component, debris in the fan Shut off immediately
    Screeching or squealing Either Bearing or belt in older equipment Service call
    Rattling that changes with speed Indoor unit Loose panel, debris, blower imbalance Inspect
    Whistling at registers Ductwork High static pressure, restricted airflow Check filter, then ductwork
    Booming at start of heating Furnace Delayed ignition, gas accumulating before lighting Shut off, service call
    Gurgling Indoor unit Condensate drain, sometimes normal Monitor drainage

    The two that should stop you using the system

    1. Metallic clanking or banging from the outdoor unit. Something is contacting something that it should not. Running it turns a small repair into a larger one, and debris in a fan can destroy the blade and motor.
    2. A boom or whoomph when heating starts. That pattern is consistent with delayed ignition, where gas accumulates briefly before lighting. It is a combustion safety concern rather than a noise complaint.
    Whistling registers are a duct message

    Air whistling through registers means it is moving through a smaller opening than it wants to. That is high static pressure, and the usual first cause is a restrictive or loaded filter. If a fresh filter does not quiet it, the ductwork is the constraint. See why static pressure matters and how filter choice affects airflow.

    Frequently asked questions

    Why is my air conditioner making a buzzing noise?

    A hum or buzz from the outdoor unit with the fan not turning usually points at a capacitor or contactor failing to start the motor, rather than at the compressor itself. The motor is receiving power but not rotating. Shut the system off to avoid overheating the motor and have it measured.

    Which HVAC noises are serious?

    Two warrant shutting the system down. Metallic clanking or banging from the outdoor unit means something is contacting something it should not, and running it worsens the damage. A boom when heating starts is consistent with delayed ignition, which is a combustion safety concern rather than a noise complaint.

    Why do my vents whistle?

    Air is being forced through a smaller opening than it wants, which indicates high static pressure. The most common first cause is a restrictive or loaded filter. If a fresh filter does not resolve it, the ductwork itself is the constraint, often undersized returns or crushed flexible duct.

    Is it normal for an HVAC system to make noise?

    Yes. Blowers, compressors and expanding ductwork all produce sound in normal operation. The diagnostic signal is change: a noise that is new, that is getting louder, or that coincides with reduced performance. A system that has always hummed quietly and now clanks has told you something.

    Methodology and limitations

    This page maps noises to mechanisms. We publish no frequencies, as no federal source measures residential HVAC fault rates by symptom.

    • Noises overlap between causes and correct diagnosis requires inspection and measurement.
    • Combustion and electrical concerns are safety matters, not maintenance items.
    • Nothing here is a diagnosis for a specific system.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • The Five Types of Air Conditioning, and How to Choose

    The Five Types of Air Conditioning, and How to Choose

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    Residential cooling comes in five forms, and the deciding factor is almost always whether the house has usable ductwork. Central split systems dominate where ducts exist; ductless mini splits dominate where they do not.

    109.51 million of 123.53 million US homes use air conditioning equipment, about 89%, per EIA survey data.

    The five types

    Type Needs ductwork Heats as well Efficiency metric
    Central split system air conditioner Yes No, paired with a furnace SEER2
    Heat pump, ducted Yes Yes SEER2 and HSPF2
    Ductless mini split No Usually yes SEER2 and HSPF2
    Packaged unit Yes Depends on configuration SEER2
    Room or window unit No Some models CEER

    Note that room units are rated on a different scale, CEER, and cannot be compared with central equipment by rating. Their minimums rose sharply for units manufactured from May 26, 2026. See our breakdown of the new levels.

    How to narrow it down

    1. Does the house have sound ductwork? If yes, central split or ducted heat pump is usually the efficient answer. If no, the cost of adding ducts is normally the largest single line in a retrofit.
    2. Do you need heat as well? A heat pump covers both in one machine. An air conditioner needs a separate heat source.
    3. Is the problem the whole house or one space? One stubborn room is a distribution problem, and upsizing the central system for it oversizes everything else.
    4. Is there space for an outdoor unit? Packaged units put everything outside, which matters where indoor plant space does not exist.
    5. Is this permanent? Rentals and short occupancies change the calculation toward room units.
    Split, packaged, ductless, in plain terms

    A split system has an outdoor unit and a separate indoor unit connected by refrigerant lines. A packaged unit puts everything in one outdoor cabinet and connects to the house with ducts. Ductless is a split system where the indoor units sit in the rooms rather than feeding ductwork.

    Frequently asked questions

    What are the types of air conditioning systems?

    Five in residential use: central split system air conditioners, ducted heat pumps, ductless mini splits, packaged units, and room or window units. The first four are rated on SEER2, while room units use a separate CEER scale that is not comparable. Whether the house has usable ductwork usually decides between them.

    What is the difference between a split and a packaged system?

    A split system separates the outdoor unit containing the compressor and condenser from an indoor unit containing the evaporator and blower, connected by refrigerant lines. A packaged unit puts all components in one outdoor cabinet and connects to the house through ducts. Packaged units suit houses without indoor plant space.

    Which type of air conditioning is most efficient?

    Central equipment and mini splits share the SEER2 scale, so rated efficiency compares directly between them. The structural difference is duct losses, which ducted systems incur and ductless systems do not. Room units use the separate CEER scale and cannot be compared by rating with either.

    Can I add central air to a house without ducts?

    Yes, but installing a duct system is normally the largest single cost in that retrofit, which is why ductless mini splits are common in houses heated by boilers or baseboards. The choice usually turns on whether ductwork can be routed sensibly rather than on the cooling equipment itself.

    Methodology and limitations

    Installed base figures are EIA RECS 2020 table HC7.1. Efficiency metrics are those defined in 10 CFR 430.32.

    • We publish no installed costs, as no federal series measures them.
    • SEER2 and CEER are different measures on different equipment classes and are not comparable.
    • Which type suits a specific house requires a load calculation for that house.

    Sources

    1. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC7.1.
    2. US Department of Energy, 10 CFR 430.32, efficiency standards.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.

  • How a Heat Pump Works, and Why It Beats 100% Efficiency

    How a Heat Pump Works, and Why It Beats 100% Efficiency

    Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards

    The short answer

    A heat pump heats by moving heat rather than making it, which is why it can deliver more heat energy than the electrical energy it consumes. A furnace can never exceed 100% of the fuel energy it burns; a heat pump routinely exceeds 100% of its electrical input because it is transporting, not generating.

    There is heat in outdoor air even in winter. A heat pump extracts it, concentrates it by compression, and releases it indoors. Running the cycle in reverse gives you air conditioning.

    Why moving heat beats making it

    Combustion converts fuel to heat, and the ceiling is the fuel’s energy content. A 95% AFUE furnace delivers 95% of it. A heat pump is not converting anything: it uses electricity to run a compressor that relocates heat that already exists outdoors.

    That is why heat pump efficiency is expressed as HSPF2 rather than as a percentage. The measure describes heat delivered per unit of electricity across a heating season, and the ratio is greater than one.

    The cycle, in heating mode

    1. Outdoor coil absorbs heat. Refrigerant colder than the outdoor air takes heat from it and evaporates.
    2. Compressor concentrates it. Raising pressure raises temperature, so the vapour becomes hot enough to be useful indoors.
    3. Indoor coil releases heat. The hot vapour condenses, giving its heat to indoor air.
    4. Metering device drops the pressure and the refrigerant returns to the outdoor coil cold enough to absorb heat again.
    5. A reversing valve swaps the roles of the two coils, which is how the same machine provides cooling.

    Why performance falls as it gets colder

    Condition What happens
    Mild outdoor temperature Plenty of heat available outdoors, cycle runs efficiently
    Colder outdoor temperature Less heat available per unit of air, compressor works harder for less output
    Below the balance point Heat pump output no longer meets the house load, supplementary heat engages
    Frost on the outdoor coil Defrost cycle runs, briefly reversing to clear ice

    The balance point is where the heat pump’s declining output crosses the house’s rising demand. Below it, supplementary heat makes up the difference, which is usually electric resistance and much less efficient. That is why cold-climate performance depends on the equipment and the house rather than on the technology alone.

    Defrost is not a fault

    A heat pump that briefly blows cool air, steams outdoors and makes a change-of-note sound is almost certainly running a defrost cycle. The outdoor coil accumulates frost because it is colder than the air around it, and the system reverses briefly to clear it. It is designed behaviour, not a failure.

    How common are they

    Heat pumps are the main heating equipment in 16.13 million US homes, about 13.1% of the housing stock, while taking close to half of new central shipments. See our shipment share analysis and our comparison against gas furnaces.

    Frequently asked questions

    How does a heat pump work for heating?

    It moves heat rather than generating it. Refrigerant colder than the outdoor air absorbs heat from it and evaporates, a compressor raises the pressure so the vapour becomes hot enough to be useful, and the indoor coil releases that heat into the house. A reversing valve swaps the coils to provide cooling instead.

    How can a heat pump be more than 100% efficient?

    Because it is not converting energy into heat, it is transporting heat that already exists. A furnace is limited by the energy content of the fuel it burns. A heat pump uses electricity to relocate outdoor heat indoors, so heat delivered can exceed electricity consumed. Performance is rated as HSPF2 rather than as a percentage.

    Do heat pumps work in cold weather?

    They operate, but output falls as outdoor temperature drops because less heat is available per unit of air. Below the balance point, where output no longer meets the house load, supplementary heat makes up the difference. Cold-climate suitability depends on the specific equipment and house rather than on the technology in general.

    Why does my heat pump blow cold air sometimes?

    Usually a defrost cycle. Frost accumulates on the outdoor coil because it runs colder than the surrounding air, and the system briefly reverses to melt it, which means the indoor side is not delivering heat for those minutes. Steam from the outdoor unit during this is normal, not a fault.

    Methodology and limitations

    Efficiency metrics are those defined in 10 CFR 430.32. Installed base figures are EIA RECS 2020. Shipment share is from the AHRI June 2026 Statistical Release.

    • We publish no coefficient of performance figures, which vary by equipment and operating condition.
    • Balance point is house and equipment specific and requires calculation.
    • Nothing here is a recommendation for a specific installation.

    Sources

    1. US Department of Energy, 10 CFR 430.32, efficiency standards and metrics.
    2. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.

    The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.