Guides
Plain-English background to the formulas behind the calculators — from what size AC you need to SEER2, AFUE, HSPF2, heat-pump-vs-gas, ventilation and right-sizing.
What size AC do I need?How to estimate air-conditioner size in BTU and tons from square footage, climate zone and adjustments — plus why a Manual J beats any rule of thumb.What is a "ton" of cooling?A ton of cooling equals 12,000 BTU per hour — here is where that number comes from, how it relates to kW and CFM, and how to convert between them.SEER vs SEER2 explainedWhat SEER, SEER2 and EER mean, why the DOE 2023 test changed the numbers, and how to use each rating to estimate cooling efficiency and running cost.AFUE explained: furnace efficiencyAFUE measures how much of a furnace's fuel becomes useful heat. Learn how to read it, what the typical bands are, and how it drives your heating cost.HSPF2 & COP explainedHSPF2 rates a heat pump's seasonal heating efficiency and COP its instantaneous efficiency. Learn how they relate, why COP falls in the cold, and how to use both.BTU explained: heating & coolingWhat a BTU is, the crucial difference between BTU and BTU per hour, and how the unit ties together sizing, capacity, fuel energy and airflow.How much does it cost to run my AC?A clear method for estimating air-conditioner running cost from capacity, EER and your own electricity rate — per hour, per day and per season.Heat pump vs gas furnace: which is cheaper to run?The fair way to compare a heat pump and a gas furnace is delivered cost per MMBTU on your own rates. Here is the method, worked with numbers.Dual-fuel systems & the balance pointA dual-fuel system runs a heat pump when it is cheap and a gas furnace when it is cold. The balance point is the temperature where you switch — here is how to find it.What size dehumidifier do I need?How to size a dehumidifier in pints per day from room area and how damp the space is, why capacity ratings changed, and how it ties into comfort.Home ventilation & ASHRAE 62.2Why modern airtight homes need mechanical fresh air, how ASHRAE 62.2 sets the required CFM, and how to check it against air changes per hour.How to read & compare HVAC quotesA practical, no-lead-gen method for comparing HVAC bids: normalize to dollars per ton, match the scope, check the load calc and read the fine print.Right-sizing: why bigger is not betterOversizing is the most common HVAC mistake. Here is what short-cycling does to comfort, humidity and efficiency — and why the right size runs longer, not harder.The heat-pump tax credit, explainedHow federal and local incentives for heat pumps generally work — the IRA 25C credit, ENERGY STAR requirements and DSIRE — and why you must confirm current amounts.