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.
m²
W/m²K (0.3 passive – 2.0 old)
°C
m³/h
W/m² (lights+equipment+people)
% (0 = none)
Envelope load
0 kW
Ventilation load (gross)
0 kW
Recovered by ERV
0 kW
Net heating load
0 kW
Annual heating energy
0 MWh/yr
Recovery share
0 %
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.
Screening estimate only, not engineering advice. Zibo Qiyu supplies air-to-air heat exchangers for ventilation load recovery — request a quote.