Heating & Cooling Load Estimator

A first-order building load estimate from envelope and ventilation. Toggle heat recovery to see how much of the ventilation load an air-to-air exchanger hands back.

Reading the numbers

Envelope load = area × U × ΔT. Ventilation load (gross) = airflow(m³/s) × 1.2 × 1.005 × ΔT. With recovery, the exchanger returns ε × ventilation load, so the net heating load = envelope + ventilation − recovered. Internal gains offset the heating need (shown as a credit in the formula but omitted here for a conservative heating estimate).

Frequently asked questions

Is this accurate enough to size a boiler?

No — it is a screening estimate. Real design needs solar, infiltration, humidity, part-load and plant efficiency. Use it to size the recovery opportunity, then do a full load calc.

Why does recovery barely move a tight building?

Because a well-insulated envelope has a small load, so ventilation dominates. That is exactly where an ERV earns its keep — see the savings tool.

What operating hours for annual energy?

The annual figure assumes the design ΔT for 2,400 h/yr (a heating-season proxy). Real annual energy is lower because ΔT is smaller most of the year.