All HVACs Calculator calculators
Pick the question you are trying to answer. Each calculator shows its formula, lists its assumptions and prints the arithmetic so you can check the result.
Air conditioning
Central AC tons, window and portable units, mini-splits, equipment heat loads and what a system costs to run.
Central AC Size Calculator
Tons and BTU/hr for a house from its floor area, climate zone, insulation, sun, windows and occupants.
AC Tonnage Converter
BTU/hr, tons, kW, watts, kcal/h and the Asian "horsepower" class, converted in one table.
Window AC Size Calculator
The BTU/hr a room unit needs from the ENERGY STAR chart, the nearest size sold and its electrical draw.
Portable AC Size Calculator
Real cooling needed (SACC) and the ASHRAE label to look for, single or dual hose.
Mini-Split Size Calculator
BTU/hr and head size for up to five zones, and the outdoor unit that serves them.
Equipment Heat Load Calculator
The cooling load that computers, appliances, lighting and people add to a room, in BTU/hr and tons.
AC Running Cost Calculator
What an air conditioner costs per hour, day and month from its size, SEER2, run time and your electricity price.
SEER Upgrade Savings Calculator
Electricity and dollars saved by a higher SEER2 rating, and how long the extra cost takes to pay back.
Heating
Furnace output and input, heat pump capacity and balance point, boilers, radiators, baseboards, space heaters, radiant floors and the cost per BTU of every fuel.
Furnace Size Calculator
Heating load in BTU/hr and the furnace input to buy, from floor area, climate zone, insulation and AFUE.
Heat Pump Size Calculator
Tons for cooling and heating, capacity at your design temperature, balance point and backup heat.
Boiler Size Calculator
Boiler output and input from the radiators or the house, with the hot-water and pickup allowances shown.
Radiator BTU Output Calculator
BTU/hr and watts from a panel, column or cast-iron radiator at your water temperature, and the room it heats.
Baseboard Heater Calculator
Watts and feet of electric or hot-water baseboard a room needs, with the circuit current for information.
Space Heater Size Calculator
Watts and BTU for a space heater as supplemental or primary heat, and the nearest size sold.
Radiant Floor Heat Output Calculator
BTU/hr a heated floor delivers at a surface temperature, whether it covers the room, and the water temperature needed.
BTU, Watts, kW and Tons Converter
Heat rates in BTU/hr, MBH, watts, kW, tons, therms per hour and boiler horsepower, plus the energy over a run.
Heating Cost by Fuel Calculator
A season of heating priced for gas, propane, oil, heat pump, electric, pellets and wood, cheapest first, with cost per million BTU.
Ducts & airflow
CFM per room and per ton, duct sizes, velocity, return grilles, registers, equivalent lengths, air changes and exhaust fans.
CFM per Room Calculator
Splits the system airflow between up to eight rooms by area and exposure, with registers per room.
Duct Size Calculator
Round and rectangular duct size for an airflow at a friction rate, checked against the velocity limit.
Duct Velocity Calculator
Air speed in a round or rectangular duct, its friction rate, and how it compares with residential limits.
Return Air Grille Size Calculator
Free area and nominal size of the return grilles for a system airflow at a quiet face velocity.
Supply Register Size Calculator
Floor, ceiling or sidewall register size and count for a room's airflow at a target face velocity.
Duct Equivalent Length Calculator
Total equivalent length of a duct run with its fittings, the available static pressure and the design friction rate.
Air Changes per Hour Calculator
ACH from a room's airflow, or the CFM for a target ACH, against common ventilation and exhaust targets.
Bathroom Exhaust Fan Calculator
Fan CFM from the code minimum, the HVI area or fixture rule and 8 air changes, with the duct run checked.
Range Hood CFM Calculator
Hood airflow from the burner BTU and hood width rules, the makeup-air threshold and the duct run.
Ventilation & humidity
Whole-house ventilation by ASHRAE 62.2, dehumidifiers and humidifiers, ERV and HRV sizing, air purifier CADR, ceiling and whole-house fans.
Whole-House Ventilation Calculator
The continuous outdoor air a house needs under ASHRAE 62.2 from its area and bedrooms, continuous or cycled.
Dehumidifier Size Calculator
Pints per day for a basement or room from its area and dampness under the 2019 rating, with the energy to run it.
Humidifier Size Calculator
Gallons per day a humidifier must add to hold a winter humidity, from the house volume, tightness and outdoor temperature.
ERV / HRV Size Calculator
The recovery ventilator size for a ventilation rate, ERV or HRV for your climate, and the heat it recovers.
Air Purifier CADR Calculator
The clean air delivery rate a room needs by the AHAM 2/3 rule or a target of 4 to 6 air changes per hour.
Ceiling Fan Size Calculator
Blade span for the room and the downrod for the ceiling height, with typical airflow and clearances.
Whole-House Fan Calculator
Fan CFM by the 2 to 3 CFM per sq ft or 15 to 20 ACH rules, the attic vent area it needs and the windows to open.
Running costs
What a system costs to run, fuels compared per million BTU, thermostat setbacks, degree days, filters, upgrade paybacks and duct leakage.
HVAC Running Cost Calculator
Cost per hour, day and month for an air conditioner, furnace, heat pump or electric heat from its output and rating.
Heat Pump vs Gas Furnace Cost Calculator
A season of heating with a heat pump against a gas, propane or oil furnace, with backup heat and the break-even price.
Thermostat Setback Savings Calculator
What lowering the thermostat at night or while out saves a season, with the heat pump caveat and the thermostat payback.
Degree Days Fuel Estimate
A season of heating fuel from the design heat loss and heating degree days, with the fuel per degree day to check bills.
Fuel Cost per Million BTU Calculator
Gas, propane, oil, electricity, heat pump, pellets and wood ranked by the cost of a million BTU of heat delivered.
HVAC Filter Cost Calculator
How often to change the furnace filter for its thickness, pets and allergies, and what a year of filters costs.
HVAC Upgrade Payback Calculator
Annual saving, payback and net gain of a more efficient furnace, boiler, AC, heat pump or water heater, after rebates.
Duct Leakage Loss Calculator
What leaky ducts in an attic, crawl space or basement cost a year, and the payback of sealing them.
Installation costs
Central AC, furnaces, heat pumps, mini-splits, ductwork, repairs and maintenance, with sourced and dated ranges.
HVAC System Replacement Cost Calculator
A sourced price range for replacing a central AC, furnace, both, or a heat pump by size, efficiency tier, ducts and region.
Mini-Split Installation Cost Calculator
Installed cost of a ductless system by number of heads, head size and type, line set, electrical work and region.
Furnace Installation Cost Calculator
Installed cost of a gas, propane, oil or electric furnace by size and efficiency, with venting, gas line and permit.
Heat Pump Installation Cost Calculator
Installed cost of a ducted, cold-climate or whole-house ductless heat pump, with electrical and duct work, after rebates.
Ductwork Cost Calculator
Installed cost of new ductwork per foot and for the house, flex or sheet metal, by access and region.
AC Repair Cost Calculator
Typical cost of common AC repairs, from capacitors to compressors, with the repair-or-replace rules applied.
HVAC Maintenance Cost Calculator
A year of tune-ups, filters and repairs paid as you go against a maintenance plan, and which is cheaper.
Water heating
Tank size by first-hour rating, tankless GPM and temperature rise, recovery time, daily hot water use, running cost and replacement cost.
Water Heater Tank Size Calculator
Peak-hour hot water demand by the DOE method and the gas, electric or heat pump tank whose first-hour rating covers it.
Tankless Water Heater Size Calculator
GPM for the fixtures running at once, the temperature rise from your groundwater, and the gas BTU or electric kW needed.
Daily Hot Water Use Calculator
Gallons of hot water a household uses a day from showers, baths, dishes and laundry, and the energy to heat it.
Water Heater Running Cost Calculator
What a gas, propane, electric, tankless or heat pump water heater costs a day, month and year for your hot water use.
Water Heater Recovery Time Calculator
How long a tank takes to reheat and how many gallons an hour it recovers, from its size, burner or element and the rise.
Water Heater Replacement Cost Calculator
Installed cost of a gas, electric, tankless or heat pump water heater, with conversion work, permit and rebates.
Planning & comfort
Zoning, lifespan and replacement timing, checking the size of an existing unit, humidity and dew point comfort, heat index, heat loss through walls and generator sizing for HVAC.
HVAC Zoning Planner
Groups up to eight rooms into zones by floor, use and exposure, with the airflow each zone needs and the warnings that matter.
HVAC Lifespan & Replacement Planner
The replacement window for an AC, heat pump, furnace, boiler or water heater from its install date, conditions and repairs.
Is My AC/Furnace the Right Size?
Compares an installed air conditioner or furnace with the house's estimated load and the symptoms of over- and undersizing.
Dew Point & Humidity Comfort Calculator
Dew point and comfort band from temperature and humidity, and whether a window, pipe or wall will condense.
Heat Index Calculator
How hot it feels from temperature and humidity by the NOAA formula, with the National Weather Service caution bands.
Heat Loss Through Walls, Windows and Roofs
BTU/hr lost through up to five walls, windows, ceilings, doors and floors from their area and R-value, and each one's share.
Generator Size for HVAC Calculator
Running and starting watts for an air conditioner or heat pump with the blower and other loads, and the generator to buy.