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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Patio Heater Guide: Propane vs Gas vs Electric, Cost per Hour and Tank Runtime
Propane, natural gas and electric patio heaters compared with EIA prices, NIST propane density and the fire code rules on balconies, clearances and tip-over switches.
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Air Curtain: How It Works, When Code Accepts One for a Vestibule, What It Saves
An air curtain blows a jet of air across an open doorway. Here is the exact IECC, ASHRAE 90.1 and Food Code language, what AMCA 220 tests, and…
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Psychrometric Chart: How to Read It, the Equations and 5 Worked HVAC Processes
How to read a psychrometric chart, with an original chart computed from the ASHRAE equations, five worked HVAC processes from the federal 80/67 rating point and the 1.08,…
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Wine Cellar Cooling Unit: Types, Sizing, Insulation and Why AC Fails at 55°F
A wine cellar cooling unit holds an insulated room near 55°F. We compare the four unit types, show how maker sizing tables change with insulation, and check the…
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Hydro Air System: How Boiler Water Heats Your Ducts, With Maker Coil Data
A hydro air system turns boiler or water heater water into ducted warm air. Maker coil tables show 140°F water gives about 64% of the 180°F output, and…
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HVAC Plenum: Supply vs Return, Sizing Rules From the Manuals and What Code Requires
An HVAC plenum is the air chamber on each side of a furnace or air handler, and in code terms a building space that moves air. Sizing rules…
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Commercial Kitchen Hood: Type I vs Type II, CFM per Foot, Makeup Air and NFPA 96
Type I versus Type II, the cfm per linear foot table by hood style and duty, the 2,000 cfm listed hood and DCKV trigger, makeup air, grease duct…
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Air to Water Heat Pump: How It Works, COP by Water Temperature and Federal Status
An air to water heat pump heats water for radiant floors, radiators and fan coils. We tabulate maker COP at 95°F to 140°F water, explain emitters, cooling and…
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Heated Driveway: How Snowmelt Works, Design Loads and the Real Cost to Run
How a heated driveway works, electric cable vs hydronic glycol loops, ASHRAE design loads, and the cost to run at EIA 2026 prices: $3.63 an hour for 400…
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Infrared Heater Explained: Types, Electricity Use, Where It Wins and Safety Rules
How an infrared heater works, the quartz, carbon, panel and gas tube types, why a 1,500 watt unit uses the same 1.5 kWh an hour as any electric…