Category: Equipment

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

Why indoor air goes dry in winter

Relative humidity is relative to temperature. Cold air holds little water vapour, so when outdoor air at freezing enters a house and is heated to room temperature, its relative humidity collapses even though the absolute amount of moisture has not changed.

The leakier the house, the worse it gets, because more of that cold, dry air is being brought in and heated. Sealing and insulating reduce the problem at source; see why envelope work comes first.

The three types

All three connect to a water line and a drain, and all three are controlled by a humidistat, which measures humidity the way a thermostat measures temperature. See how thermostats work for the control logic.

Maintenance, which is the whole game

A neglected humidifier is worse than none, because it is a warm wet surface in the air path.

1. Replace the water panel or pad at least once a heating season, more in hard water.
2. Check the drain for blockage, and confirm water is actually leaving.
3. Shut the water off in spring and close the damper on bypass models, or it will run through the cooling season.
4. Watch the humidistat setting as outdoor temperature drops. The colder it gets outside, the lower the indoor setting has to be to avoid condensation.

What it will not fix

A humidifier will not fix a draughty house, a dusty one, or a duct system that cannot move air. Adding moisture to air that is not circulating produces damp in one room and dry air in another. If airflow is the underlying issue, see ductwork and airflow and how filters affect airflow.

No federal source measures health outcomes or energy savings from whole-house humidifiers, and we publish neither.

Frequently asked questions

Methodology and limitations

Humidity guidance is quoted from EPA’s mould course materials. Equipment descriptions are general to residential ducted systems.

• No federal source measures health outcomes, comfort or energy savings from whole-house humidification.
• We publish no installed prices, because none is federally measured.
• Correct settings vary with outdoor temperature and window construction.

Sources

1. US Environmental Protection Agency, Mold Course, Chapter 2, indoor relative humidity guidance.

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.

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

Federal minimums by boiler type

The standards apply by product class, and the design requirements attached to them matter as much as the efficiency figure.

Standby and off-mode power are also capped, at 9 watts for gas hot water boilers and 11 watts for oil. The standards attach to the date the boiler was manufactured, not to when it is installed.

Condensing or non-condensing

This is the choice that drives the rest of the job. A condensing boiler extracts heat from the flue gases until water vapour condenses, which is where the extra efficiency comes from.

The last row is the one that gets missed. A condensing boiler connected to old cast iron radiators run at high water temperature will not condense much of the time, so it will not deliver its rated efficiency. Our page on radiant floor heating covers the low temperature case where condensing boilers do their best work.

Sizing, and why bigger is worse

Boilers are commonly replaced like for like, which repeats whatever oversizing the original install had. An oversized boiler short cycles: it satisfies the thermostat quickly, shuts down, and starts again, which wastes fuel and wears the burner.

A heat loss calculation for the building is the correct basis, the boiler equivalent of a Manual J load calculation. Ask for it, and ask what the radiator or emitter output is at the water temperature the new boiler will actually run.

What it costs to run

At 2025/26 heating season average prices and federal minimum efficiencies, heat from an 84% gas boiler cost about $17.92 per million Btu delivered, against $33.68 from an 86% oil boiler.

Fuel price dominates that comparison, not the few points of efficiency between classes. The full table, including heat pumps and electric resistance, is in what heat costs by fuel. For how boiler systems distribute that heat, see boilers and baseboard heating.

What to ask before signing

• What heat loss calculation was done, and what output did it give?
• Condensing or not, and if condensing, what return water temperature will the system run at?
• Where does the flue terminate, and what happens to anything else on the old chimney?
• Where does the condensate drain, and does it need neutralising?
• What is the AFUE of the specific model, and what is its standby power?

Our contractor checklist covers the licence, permit and warranty side of the same conversation.

Frequently asked questions

Methodology and limitations

Efficiency and design requirements are quoted from 10 CFR 430.32(e)(2). Household counts are EIA RECS 2020 table HC6.1. Running costs come from our fuel cost page, which uses EIA season average prices and federal minimum efficiencies.

• Standards apply to manufacture date, not installation date.
• We publish no installed prices, because no federal series measures them.
• Heat loss calculation procedures are private industry standards, which we name but do not reproduce.

Sources

1. Code of Federal Regulations, 10 CFR 430.32(e)(2), residential boiler standards.
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.

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

How federal efficiency rules work here

Water heaters are rated by Uniform Energy Factor, and the minimum is a formula rather than a fixed figure. It varies by product class, storage volume and draw pattern, which is why any page quoting “the minimum UEF” has quietly fixed all three.

Under 10 CFR 430.32(d), a gas-fired storage water heater between 20 and 55 gallons on a medium draw pattern must reach a UEF of 0.6483 minus 0.0017 times the rated volume. A 50 gallon unit therefore needs about 0.563. The equivalent electric storage class needs 0.9307 minus 0.0002 times volume, about 0.921.

That last row is the important one. A UEF above 1.0 means the appliance delivers more energy than it consumes, which resistance elements cannot do. The large electric classes are effectively heat pump water heaters by regulation.

What changes in 2029

A second table in the same section applies to units manufactured on or after May 6, 2029, and it is based on effective storage volume rather than rated volume. It also adds classes below 20 gallons and above 100 gallons that the current table does not cover.

This affects manufacture date, not your installation. A compliant heater built before that date remains legal to sell and install afterwards, the same principle that governs SEER2 minimums for cooling equipment.

Sizing: first hour rating, not gallons

Tank size is the number everyone quotes and the wrong one to buy on. The useful figure is the first hour rating, how much hot water the unit can deliver in the busiest hour, which combines tank volume with recovery rate.

1. Work out your peak hour, usually a morning: showers, a dishwasher, a laundry load.
2. Add the demand in gallons for that hour.
3. Match the first hour rating to that figure, not to the tank size of the old unit.
4. For tankless, the equivalent is flow in gallons per minute at your incoming water temperature. Cold inlet water cuts deliverable flow, so a unit sized for a southern climate underperforms in a northern one.

A heat pump water heater has a further constraint: it needs air volume and clearance around it, and it cools and dehumidifies the space it sits in.

Fuel cost, honestly

Water heating cost follows the same fuel prices as space heating. At 2025/26 season averages, natural gas cost about $15.05 per million Btu of fuel against about $52.10 for electricity.

That gap is why gas has been cheaper to run, and why a heat pump water heater changes the comparison: by moving heat rather than making it, it uses a fraction of the electricity a resistance element does. Our page on what heat costs by fuel sets out the arithmetic and the assumptions behind it.

What the market is doing

Shipments are falling on both fuels. Through July 2026, gas storage water heater shipments were 2,487,389 units, down 2.5% on 2025, and electric storage was 2,877,192, down 5.2%.

Electric is also down 5.5% against the same period of 2024, so this is a two-year decline rather than one soft season. More in our water heater shipments and standards report.

Frequently asked questions

Methodology and limitations

Efficiency requirements are quoted from 10 CFR 430.32(d). Rulemaking history is from Federal Register documents 89 FR 105188, 90 FR 9951, 90 FR 13054 and 90 FR 21390. Shipments are AHRI’s July 2026 release. Fuel prices are EIA season averages as documented on our fuel cost page.

• Worked UEF examples assume a medium draw pattern; other draw patterns have different formulas.
• Standards apply to manufacture date, not installation date.
• We publish no installed prices or payback periods, because no federal series measures them.

Sources

1. Code of Federal Regulations, 10 CFR 430.32(d), water heater energy conservation standards.
2. US Department of Energy, “Energy Conservation Standards for Consumer Gas-Fired Instantaneous Water Heaters”, final rule 89 FR 105188 (December 26, 2024) and final rule; withdrawal, 90 FR 21390 (May 20, 2025).
3. Air-Conditioning, Heating, and Refrigeration Institute, July 2026 shipment release.

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.

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

The faults that are specific to heat pumps

These four have no equivalent on a cooling-only system, and they are where a general air conditioning diagnosis goes wrong.

Normal behaviour that looks like a fault

Heat pumps behave differently from furnaces, and three normal behaviours generate service calls.

• Defrost cycles. In cold, damp weather the outdoor coil frosts. The unit periodically reverses to melt it, which produces steam, dripping and a few minutes of cooler air indoors. This is designed behaviour.
• Cooler supply air. A heat pump delivers air cooler than a furnace does. It feels lukewarm at the register while still heating the house.
• Long run times. Heat pumps are meant to run for long periods at low output. Short, fierce cycles are the problem, not long gentle ones.

Our explainer on how a heat pump works covers the cycle these behaviours come from.

The faults it shares with any air conditioner

Everything in the refrigeration circuit and the electrical path fails the same way it does on a cooling-only system: capacitors, contactors, fan motors, compressors, and refrigerant leaks.

A heat pump works the circuit harder, because it runs in both seasons rather than one. That is the argument for servicing it twice a year rather than once. See capacitor failures and what a tune-up should include.

What repairs cost

No federal series measures heat pump repair prices, and the range that matters most, a reversing valve or compressor replacement against the cost of a new system, is exactly the one nobody measures.

Two questions make a quote comparable. What refrigerant does the system use, since an R-410A system faces a tightening supply under the phasedown schedule. And what was measured, in pressures and temperatures, to reach the diagnosis.

Frequently asked questions

Methodology and limitations

Component behaviour is described in general terms for residential air-source heat pumps. Household counts are EIA RECS 2020 table HC6.1. Running cost comparisons come from our fuel cost page, which uses EIA season average prices and federal minimum efficiencies.

• No federal source measures repair prices or failure rates, and we publish neither.
• Defrost behaviour varies by manufacturer and control strategy.
• Nothing here is a diagnosis for a specific system.

Sources

1. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.
2. Code of Federal Regulations, 10 CFR 430.32(c), heat pump 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.

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

What actually fails, by symptom

Furnaces mostly fail in one of four ways, and each points at a different group of parts.

The single most common no-heat pattern is a furnace refusing to light because a safety interlock has not proved. Our page on why a furnace will not ignite walks the start sequence step by step.

The parts that fail most

These are wear items on a gas furnace. Each is cheap relative to the machine, and each stops the furnace completely.

1. Hot surface igniter. A brittle ceramic element that glows to light the burners. It fails from age and from being touched.
2. Flame sensor. A metal rod that proves a flame is present. It gets coated and stops conducting, so the furnace lights and immediately shuts down.
3. Pressure switch. Confirms the inducer is drawing properly. A blocked flue or a cracked hose will keep it open, and the furnace will not fire.
4. Capacitor. Starts and runs the blower motor. See what a capacitor does.
5. Blower motor. Moves the heated air. See blower motor symptoms and types.
6. Limit switch. Shuts the furnace down when it overheats, usually because airflow is restricted. A limit switch that trips repeatedly is reporting an airflow problem, not causing one.

Repair or replace

Three things decide it, and age alone is not one of them.

• What failed. An igniter or a capacitor is a routine repair. A heat exchanger, a control board on an old furnace, or a second major failure in a season pushes towards replacement.
• What the furnace is. An 80% AFUE furnace replaced today can be a condensing model; from December 18, 2028 new non-weatherized gas furnaces must be 95% AFUE, which changes venting. See the 2028 standard.
• Whether it is still safe. Combustion faults are not a cost question.

Age is a weak signal on its own: 20.0% of US homes that heat are running main heating equipment 20 years old or more, and most of it works.

What a furnace repair costs

No federal series measures HVAC repair prices. BLS publishes producer prices for equipment and wages for the trade, but nothing that tells you what a flame sensor replacement costs in your town.

What you can do is make quotes comparable: ask for the part and the labour separately, ask what failed and why, and ask what the technician measured. A part that fails twice in two seasons is a symptom of something else. Our page on what HVAC repair costs are actually measured explains the gap.

How much furnace repair there is to do

The installed base is large and old. A central warm-air furnace is the main heating equipment in 74.42 million US homes, 63.2% of homes that heat, and gas furnace shipments are running below last year, which means more of that base is being repaired rather than replaced.

Frequently asked questions

Methodology and limitations

Component descriptions are general to residential gas furnaces. Carbon monoxide figures are CPSC 2022 annual estimates, published May 2026. Installed base is EIA RECS 2020 table HC6.1.

• We publish no repair prices, because no federal series measures them.
• CPSC estimates are for consumer products under its jurisdiction and are revised in later reports.
• Nothing here is a substitute for a qualified technician inspecting your equipment.

Sources

1. US Consumer Product Safety Commission, Home Heating Equipment and Non-Fire Carbon Monoxide Deaths Associated with the Use of Consumer Products, 2022 Annual Estimates (May 2026).
2. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.
3. Code of Federal Regulations, 10 CFR 430.32(e), furnace 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.

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

What a capacitor does

A capacitor stores electrical charge and releases it in step with the motor. That shifts the timing of current in a second motor winding, which gives a single-phase motor the push it needs to start and the balance it needs to run efficiently.

Without it, a compressor or fan motor receives power but cannot turn, or turns weakly. That is why a failed capacitor so often looks like a failed motor from the outside, and why the two are told apart by measurement rather than by looking. See what an AC condenser does for the rest of the outdoor unit.

Start, run and dual run capacitors

Residential systems use two kinds of job, sometimes combined in one part: a run capacitor that stays in the circuit, and a start capacitor that helps only at start-up.

Signs a capacitor has failed

Most capacitor symptoms are about motors not starting properly. Each one has other possible causes, which is why a technician tests before replacing anything.

• The outdoor unit hums but the fan does not turn. The most common pattern. A failed contactor or a seized motor can look the same. More in what HVAC noises mean.
• The compressor tries to start and trips the breaker. A weak start or run capacitor is one cause; a failing compressor is another.
• The fan starts slowly or not at all while the compressor runs.
• The system runs but blows warm air. If the compressor is not starting, the indoor blower can still move uncooled air. See AC running but not cooling.
• A visibly swollen or leaking case. A domed top is a clear sign, but many failed capacitors look perfectly normal.

If the outdoor unit is humming without starting, switch the system off at the thermostat. A motor that keeps receiving power without turning can overheat.

Reading the label

Every capacitor is printed with its capacitance in microfarads, shown as µF or MFD, and a voltage rating, commonly 370 or 440 volts AC on residential equipment.

A replacement should match the capacitance the equipment calls for and meet or exceed the voltage rating. On a dual run capacitor both capacitance values matter, one for the compressor and one for the fan. The equipment wiring diagram, not the old part alone, is the reference, because the old part may itself be the wrong one.

Why a small part matters

A capacitor is cheap; the motors it serves are not, and they are getting more expensive. The BLS producer price index for motor and generator manufacturing reached 318.1 in 2026-08, up 3.9% on a year earlier and 47.5% above its 2019 average.

That is a factory-gate index for motors in general, not a price for HVAC replacement motors. It still makes the practical point: dealing with a failing capacitor promptly costs less than letting a motor strain against it.

What a capacitor replacement costs

No federal series measures HVAC repair prices, so any figure you see for a capacitor replacement is a vendor survey or a contractor estimate. We do not publish one.

The part is inexpensive and the visit is short, which puts it at the low end of HVAC repairs. Ask for part and labour separately, and ask why it failed: a capacitor that fails twice in two seasons points to a different problem. Our page on what HVAC repair costs are actually measured explains the gap in the data.

Frequently asked questions

Methodology and limitations

This page describes how motor capacitors work in residential air conditioners and heat pumps in general terms. Equipment-specific ratings come from the manufacturer’s wiring diagram and data plate.

• No federal source measures capacitor failure rates or replacement prices, and we publish neither.
• The motor price index is BLS series PCU335312335312, not seasonally adjusted, and covers motors broadly rather than HVAC replacement parts.
• Nothing here is electrical safety advice for a specific installation.

Sources

1. US Bureau of Labor Statistics, Producer Price Index series PCU335312335312, motor and generator manufacturing.
2. US Environmental Protection Agency, Section 608 of the Clean Air Act, refrigerant management requirements.

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.

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

How forced-air central heating works

A furnace heats air and a blower pushes that air through ducts. The flame or element never touches the air you breathe; a heat exchanger sits between them.

1. The thermostat calls for heat.
2. The furnace produces heat, by burning gas, propane or oil, or by passing current through electric resistance elements.
3. A heat exchanger transfers that heat to the air while keeping combustion gases in a separate path.
4. The blower pushes warmed air into the supply ducts and out through registers in each room.
5. Return ducts draw cooler room air back to the furnace, through the filter, to be heated again.
6. Combustion gases vent outdoors through a flue or, on high-efficiency condensing furnaces, through plastic vent pipe.

A heat pump does the same distribution job but moves heat from outdoor air instead of making it. See heat pump versus gas furnace.

What US homes heat with

Forced air dominates. The central furnace alone is the main system in more homes than every other type of heating equipment combined.

Figures are EIA RECS 2020, table HC6.1, and may not sum exactly because of rounding. Fuel shares across all equipment types are covered in how American homes are heated.

Does central heating use gas?

Usually, but not always. Of the 74.42 million homes heating mainly with a central furnace, 71.6% burn natural gas.

Electric furnaces are the second largest group. They have no flame and no flue, and they convert electricity to heat one for one, which makes them expensive to run where electricity is expensive.

Forced air versus hot water

Both are central heating. The difference is what carries the heat: air through ducts, or water through pipes to radiators, baseboards or floors.

More on the water side in radiant floor heating.

Federal efficiency minimums for furnaces

A new non-weatherized gas furnace must reach 80% AFUE today, and 95% for units manufactured from December 18, 2028, under 10 CFR 430.32(e).

AFUE is determined under the federal test procedure, so these are rating floors rather than measured performance in a given house. The 2028 change and what it means for venting is covered in the 95% furnace standard.

What central heat costs to run, by fuel

At 2025/26 heating season average prices, heat from an 80% gas furnace cost about $18.81 per million Btu delivered, against $52.10 from an electric furnace and $23.70 from a minimum-efficiency heat pump.

The full comparison, including propane, oil and the prices used, is in what heat costs by fuel.

How old heating systems are

Heating equipment is kept much longer than cooling equipment. 20.0% of homes that heat run main heating equipment 20 years old or more, against 9.6% of air conditioned homes for cooling equipment.

Ages are reported by households, grouped in bands, and cover all main heating equipment, including long-lived boilers.

Frequently asked questions

Methodology and limitations

Household counts and ages are EIA RECS 2020, table HC6.1. Efficiency minimums are quoted from 10 CFR 430.32(e). Running costs use EIA season average prices and federal minimum efficiencies, as documented on our fuel cost page.

• RECS 2020 is a survey estimate and the latest vintage for equipment data, with the 2024 survey’s equipment tables due in spring 2027 See what the 2024 survey release covers.; we do not project it forward.
• Furnace fuel rows do not sum to the furnace total because of rounding and suppressed cells.
• We publish no installed prices, because no federal series measures them.

Sources

1. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.
2. Code of Federal Regulations, 10 CFR 430.32(e), furnace and boiler 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.

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

How central air works

A central air conditioner does not make cold air. It moves heat from inside the house to outside, using refrigerant that absorbs heat at the indoor coil and releases it at the outdoor coil.

1. The thermostat calls for cooling. It switches on the outdoor unit and the indoor blower.
2. The blower pulls room air through the return ducts and pushes it across the indoor evaporator coil.
3. Refrigerant in the coil evaporates and absorbs heat from that air. Moisture condenses on the cold coil and drains away, which is how central air dehumidifies.
4. The compressor in the outdoor unit pumps the refrigerant vapour up to high pressure and temperature.
5. The outdoor condenser coil and fan release the heat to outside air, and the refrigerant condenses back into a liquid.
6. An expansion device drops the pressure and the cold refrigerant returns indoors, while the cooled air leaves through the supply ducts.

The parts of a central air system

Every central system has the same core parts split between an outdoor cabinet and an indoor section, joined by refrigerant lines and served by ductwork.

The outdoor unit is covered in detail in what an AC condenser does. Ducts decide more of a system’s real performance than most owners expect, which is why ductwork and airflow problems so often get blamed on the equipment.

How many homes have central air

Central equipment is the main cooling system in 66.9% of all US homes. It is close to standard in houses and noticeably less common in apartments.

Another 14.02 million homes use no air conditioning at all.

Central air versus the alternatives

The real choice is between systems that need ducts and systems that do not. Central air and central heat pumps need them; mini-splits, window units and portables do not.

A central heat pump is the same machine as central air with a reversing valve added, so it can run the cycle backwards in winter. See how a heat pump works.

Does central air use gas?

No. The compressor, fans and controls all run on electricity. The confusion comes from the furnace: in a house with a gas furnace, central air shares the furnace blower and ducts, so the two look like one appliance.

The word gas also gets used loosely for refrigerant. Refrigerant is a working fluid that circulates in a sealed loop, not a fuel that gets burned, and a correctly working system does not use it up.

What the federal efficiency rules require

New central air conditioners must meet a minimum SEER2 rating set by the Department of Energy, and for split systems the minimum depends on where the system is installed.

Under 10 CFR 430.32, the Southeast covers Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, the District of Columbia and US territories. The Southwest is Arizona, California, Nevada and New Mexico. The regional rules apply to systems installed on or after January 1, 2023. Our SEER2 guide covers how the rating works.

How old central air systems are

About one in five air conditioned homes runs main cooling equipment that is at least 15 years old: 21.56 million homes, or 19.7%.

These bands cover all main cooling equipment, not central systems alone, and ages are as reported by households. RECS publishes the distribution but no average age and no failure rate. Our guide to HVAC lifespan explains what that does and does not tell you.

Frequently asked questions

Methodology and limitations

Household counts are from EIA RECS 2020 table HC7.1, the latest vintage for equipment data, and include central heat pumps in the central category. Efficiency minimums are quoted from the Code of Federal Regulations.

• RECS 2020 is a survey estimate with sampling error, and we do not project it forward.
• Equipment age is reported by households, grouped in bands, and covers all main cooling types.
• We publish no installation prices, because no federal series measures them.

Sources

1. US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC7.1.
2. Code of Federal Regulations, 10 CFR 430.32(c)(5) and (c)(6), energy conservation standards for central air conditioners and heat pumps.

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.

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

How radiant floor heating works

Heat passes from a warm floor surface directly to people and objects in the room, rather than being carried by moving air. There are no ducts to lose heat along the way.

DOE separates installations into two kinds. “Wet” installations embed tubing or cables in a concrete slab or lightweight concrete, using its thermal mass. “Dry” installations run them in an air space under the floor, which is faster and cheaper to build but needs the system to run at a higher temperature.

Hydronic, electric and radiant air floors

Of the three types, DOE calls hydronic systems “the most popular and cost-effective radiant heating systems for heating-dominated climates.”

Hydronic systems can heat the water with gas or oil boilers, wood-fired boilers or solar water heaters. Our guide to boilers and baseboard heating covers the boiler side.

What radiant floor heating costs to run

The floor only distributes heat; the source sets the running cost. At 2025/26 season prices and federal minimum efficiencies:

Federal AFUE minimums for hot water boilers are 84% for gas and 86% for oil under 10 CFR 430.32(e)(2); electric hot water boilers have no AFUE minimum. For how these compare with furnaces and heat pumps, see what heat costs by fuel.

Which floor coverings work

DOE says ceramic tile “is the most common and effective floor covering for radiant floor heating, because it conducts heat well and adds thermal storage.” Anything that insulates the floor from the room lowers efficiency.

• Tile and stone: the best match.
• Carpet: use thin carpet with dense padding, and as little as possible.
• Wood: DOE recommends laminated wood flooring over solid wood, to reduce shrinking and cracking.
• Mixed rooms: rooms with a different covering should have their own tubing loop, because water under a covered floor has to run hotter.

The disadvantages

The main drawbacks are slow response, no cooling, and cost and disruption to install in an existing home.

• Slow response. DOE notes thick slabs have a “slow thermal response time, which makes strategies such as night or daytime setbacks difficult if not impossible,” and most experts recommend a constant temperature.
• No cooling. A radiant floor heats only. Cooling needs a separate system, such as a ductless mini-split.
• Installation cost. DOE says hydronic installation cost varies with location, home size, installation type, floor covering, site remoteness and labour. No federal series measures it.
• Floor limits. Coverings and floor build-up are constrained, especially in retrofits.

How many homes use it

EIA does not count radiant floors separately. Its Residential Energy Consumption Survey reports that 9.29 million homes, 7.9% of those that heat, use a steam or hot water system as their main heating equipment, a group that includes radiators, baseboards and radiant floors. Forced air is far more common; see what central heating is.

Frequently asked questions

Methodology and limitations

DOE statements are quoted from its Energy Saver guidance on radiant heating, which no longer resolves at energy.gov; we cite the archived copy. Running costs use EIA 2025/26 season average prices and federal minimum efficiencies, documented on our fuel cost page.

• We publish no installed prices, because no federal series measures them.
• Costs exclude distribution pumps, boiler standby losses and fixed utility charges.
• RECS 2020 does not separate radiant floors from other hot water systems.

Sources

1. US Department of Energy, Energy Saver: Radiant Heating, archived copy.
2. Code of Federal Regulations, 10 CFR 430.32(e)(2), residential boiler standards.
3. 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.