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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Low Water Cutoff: How Float and Probe LWCOs Work, Code Rules, Testing and Reset
A low water cutoff stops a boiler’s burner before it dry fires. How float and probe types work, where the IRC and state rules require one, maker test…
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Nitrogen Pressure Test: PSI by Manufacturer, Hold Times and Temperature Correction
How to nitrogen pressure test AC lines: test pressures and hold times from Goodman, Daikin, Mitsubishi and Rheem manuals, a worked temperature correction, brazing purge and the EPA…
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Ducted Mini Split: Static Pressure Limits, Ratings and Duct Design Rules
A ducted mini split hides the indoor unit and feeds a few rooms through short ducts. Here are the maker static pressure limits, how its ratings compare with…
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Electronic Air Cleaner: How It Works, Ozone, Cleaning and MERV
An electronic air cleaner charges particles and collects them on washable plates. We checked the ozone numbers, CARB rules, Honeywell and Trion cleaning guidance and the MERV 13…
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Indirect Water Heater: How It Works, Sizing, Priority Zones and Federal Rules
An indirect water heater is a boiler-heated storage tank with no burner of its own. How the coil and priority zone work, how to size one by first-hour…
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Aquastat Explained: High Limit, Low Limit, Differential and Boiler Settings
What an aquastat does, how high limit, low limit and differential work, and what the Resideo, Beckett and Hydrolevel manuals and state codes actually say about settings and…
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Refrigerant Oil: POE vs Mineral, PVE, What R-410A Uses and When You Can Mix
Refrigerant oil follows the refrigerant: mineral or alkylbenzene for R-22, POE or PVE for R-410A, POE for R-454B and R-32. Copeland, Danfoss, Rheem and oil maker data on…
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Dedicated Outdoor Air System (DOAS): How It Works, Federal ISMRE2 Rules and Codes
A dedicated outdoor air system treats all ventilation air separately from room heating and cooling. Here is how a DOAS works, the federal ISMRE2 minimums since May 1,…
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Crankcase Heater: What It Does, When It Is Required and What It Costs to Run
A crankcase heater keeps refrigerant from condensing in compressor oil during off cycles. Here is when Copeland requires one, why manuals say 24 hours before startup, and what…
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Schrader Valve on AC Systems: Cores, Caps, Port Sizes, Leaks and Locking Cap Code
A Schrader valve is the access valve in every AC service port. Here are the maker torque specs, 1/4 and 5/16 in. port threads, how leaking cores are…