Eight free calculators for sizing, replacing, and comparing home heating and cooling systems: load and AC sizing, boiler sizing, full replacement cost, refrigerant comparison, and heat pump efficiency, payback, and cold-weather performance.
This page is for sizing, replacing, or comparing a home heating and cooling system, whether you are getting a contractor quote for a new unit, deciding between two heat pump models, or trying to understand how much efficiency a heat pump actually loses once it gets cold outside.
Start with HVAC Load Sizing or What Size AC Do I Need if you do not yet know what size unit your home needs; a unit sized wrong is the single biggest reason an HVAC system runs inefficiently. Once you know the size, use Heat Pump COP Product Comparison to compare specific models, then Heat Pump Payback to see how long a heat pump takes to pay for itself after rebates, and HVAC Replacement Cost for the full line-item bill.
What size HVAC unit does my home actually need?
What size AC do I need, in plain English?
What size boiler does my home need, and what will fuel cost?
What will a full HVAC replacement actually cost, line by line?
How do R-410A and R-454B compare on cost and climate impact?
How much efficiency does my heat pump lose in the cold?
How do two heat pump models compare at my winter temperatures?
How long until a heat pump pays for itself after rebates?
A heat pump's rated efficiency (COP, HSPF2, SEER2) is measured under lab conditions at specific outdoor temperatures, which is why the same model can look great in one climate zone and mediocre in another. ENERGY STAR's air-source heat pump page covers cold-climate performance in its own "Cold Climate Considerations" section, separate from a model's standard rating, and the Department of Energy's climate zone guidance lets you look up your climate zone by county or zip code before comparing two units.
How we source our numbers: every calculator on this page uses current government or published-standard figures, not a guess. The full method for each one, and how we correct a number when it changes, is on our methodology page; our sourcing and correction rules are on our editorial policy page. Reviewed September 2026.
No, an oversized unit short-cycles, wearing out faster and dehumidifying poorly. The HVAC Load Sizing Calculator is built to find the actual right size, not the safest-sounding bigger number.
A heat pump's coefficient of performance is measured at a specific outdoor temperature, and heat pumps lose efficiency as it gets colder. The Heat Pump COP Derating Calculator models that drop directly.
It depends on square footage, insulation, climate zone, and window exposure, not just square footage alone. The HVAC Load Sizing Calculator uses your climate zone from the Department of Energy's climate zone guidance rather than a single national rule of thumb.