Equipment
Heat pumps, furnaces, air conditioners, boilers and water heaters: how they work, what they cost, how long they last and which efficiency standards apply.
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HVAC Transformer: 24V Control Power, VA Sizing, Testing and Why It Blows
The 24 V control transformer explained from maker documents: what 40 VA really carries, how technicians test it, and why a transformer or board fuse that keeps blowing…
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Outdoor Wood Boiler: How It Works, EPA Step 2 Rules, State Limits and Cost to Run
How an outdoor wood boiler works, what EPA’s Step 2 limit requires, how New York, Massachusetts and Wisconsin restrict siting, and the cordwood price that matches oil and…
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Mobile Home Furnace: HUD Code Rules, the 2028 Efficiency Floor and Replacement
A mobile home furnace is a direct vent furnace listed for manufactured homes. Here are the HUD Code rules, the 95% AFUE floor from December 2028, and a…
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Fire Damper: Where Code Requires Them, Fusible Links and the Inspection Clock
A fire damper closes a duct where it crosses a fire-rated wall or floor. Here is where IBC Section 717 requires them, fire vs smoke vs combination dampers,…
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Circulator Pump: How It Works, Sizing Math, ECM Rules and Failure Signs
How a boiler circulator pump works, how to size one with GPM = Btu/h ÷ (500 × ΔT), what Taco and Grundfos data show on watts, and what…
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Window Heat Pump: How It Works, Cold Weather Specs and What It Costs to Run
A window heat pump heats and cools from one 120 V plug. We compare Midea and Gradient cold weather specs, the NYCHA pilot results, DOE ratings and the…
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Inducer Motor: What It Does, Symptoms of Failure and Safe Replacement
What a furnace inducer motor does, how long it runs before ignition, shaded pole vs PSC vs variable-speed types, a symptom checklist and the sealing rules for replacement,…
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Flex Duct: How It Is Built, What Sag and Compression Cost, and the Install Rules
Flex duct moves air about as well as sheet metal when pulled taut. LBNL and Texas A&M lab tests show compression and sag multiply its pressure loss, and…
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Boiler Pressure: Normal PSI, Too High, Too Low and Steam Settings From the Manuals
Normal boiler pressure from named US boiler manuals: 12 psi cold, a 24 psig hot ceiling and a 30 psi relief valve, plus why pressure runs high or…
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Zone Valve: How It Works, 2 vs 3 Wire, and Why It Is Not Opening
How a hydronic zone valve works, what 2, 3 and 4 wire valves do, and the order to check a zone valve that will not open, using Resideo,…