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HVAC Sizing Calculator

Estimate the heating and cooling load of a room in BTU/hr, kW and tons from its area, climate and insulation.

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HVAC Sizing Calculator is free to use as often as you like, directly from this page. It sits under Energy & power in our catalogue, alongside Appliance Energy Cost Calculator and Electricity price today.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.
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Frequently asked questions

What is HVAC Sizing Calculator?

Estimate the heating and cooling load of a room in BTU/hr, kW and tons from its area, climate and insulation.

When would I actually use this?

Putting a number on a bill: what an appliance costs to run, whether a solar array covers the load, and how much heating a room actually needs.

What is the most common mistake?

Confusing power with energy. A kilowatt is a rate and a kilowatt-hour is a quantity; a 2 kW heater on for half an hour uses 1 kWh, and only the second figure appears on a bill.

Is there a tool for the next step?

Electricity price today is the closest one after this: Today's and tomorrow's wholesale electricity prices per quarter hour for 16 European zones, with the cheapest hours, the daily average and negative prices.

What else is worth having open alongside it?

Heat Loss Calculator and Home Energy Audit Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The arithmetic is exact for the rating and the tariff you enter. Nameplate wattage is a maximum, not an average, and solar output depends on latitude, orientation and shading that no formula can guess.

Further reading

All guides →
ComparisonInsulate or Replace the Heating: Which Repays First, and Why the Answer InvertsPut both on one axis — euros paid per kilowatt-hour a year of permanent saving — and the comparison becomes decidable. The same loft job costs 0.83 euros per kilowatt-hour a year in a 1965 house and 5.00 in a 2005 one, a factor of six. That, and not the age of the building by itself, is what inverts the verdict.ExplainerA 5,000 mAh Power Bank Does Not Hold 5,000 mAh for Your Phone5,000 mAh drawn at 500 mA with 85 % efficiency runs for 8.5 hours instead of the arithmetic's 10. The same 15 % explains why a 5,000 mAh bank barely fills a 4,000 mAh phone once.ComparisonHeat Pump or Gas Boiler: the SCOP Your Local Prices DemandBefore any grant, the price of electricity divided by the price of gas sets a seasonal efficiency the heat pump must beat just to break even on running cost. In late 2025 that number was 1.53 in Portugal and 2.79 in Germany — and on old radiators a German heat pump can cost more to run than the boiler it replaced.ExplainerR-Values, U-Values, and What an Insulation Number HidesR and U are reciprocals, and the two markets that read this site use different ones in different units — so an R-value quoted without its system means nothing. Worse, the number on the batt is not the number your wall achieves, because the studs are a parallel path.How-toHow to Estimate the Running Costs of a HomeAdd up energy, water, heating, and maintenance with simple rules of thumb so you know what a home really costs to run each month.How-toHow Much Does a Space Heater Cost to Run?Multiply the heater's kilowatts by hours used and your price per kWh — a 1.5 kW heater for 5 hours a day adds up fast at typical tariffs.
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