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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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Appliance Energy Cost CalculatorTurn any appliance's wattage and daily use into a daily, monthly and yearly running cost in your currency.Heat Loss CalculatorAdd up the conductive heat loss through walls, windows, doors and roof from their area and R- or U-value.Home Energy Audit CalculatorEstimate your home's annual energy use, cost, intensity and HVAC share from its shell and major appliances.Insulation CalculatorFind the recommended R-value for your climate and component, and how much insulation you still need to add.Light Bulb Savings CalculatorCompare LED, incandescent and CFL bulbs on yearly energy plus replacement cost, and see your LED savings.Power Factor CalculatorCompute power factor, apparent and reactive power, and PF-correction capacitance.Amperage CalculatorConvert a load in watts and a supply voltage into the current drawn in amps.Appliance running cost calculatorEstimate what an appliance costs to run per day, month and year.

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 Heat Loss Calculator.

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.

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?

Heat Loss Calculator is the closest one after this: Add up the conductive heat loss through walls, windows, doors and roof from their area and R- or U-value.

What else is worth having open alongside it?

Home Energy Audit Calculator and Insulation 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.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.How-toHow Many Amps Does an Appliance Draw?Divide the appliance wattage by the supply voltage to get the current in amps — the number that decides breaker size, wire, and what can share a circuit.How-toWhat Wire Gauge Do I Need?Pick wire size from the load current, run length, and allowed voltage drop — the amps decide the minimum cross-section, distance forces you thicker.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.