Heat recovery ventilation: Calculate heat savings and running costs
A ventilation system with heat recovery can transfer heat from the exhaust air to the fresh air. At the same time, the system uses electricity and requires maintenance. The calculator combines these factors in an estimate of the economics.
Worked example
- Airflow: 100 m³/h
- Heating degree days: 2,500
- Recovery: 80 %
- Efficiency of the heating system: 90 %
- Price per kWh of purchased energy: 0.11 GBP
- Extra electricity for fans: 400 kWh/year
- Electricity price: 0.23 GBP
- Filters and service: 68.00 GBP
Recovered heat
1,632 kWh per year
Ventilation loss without recovery 2,040 kWh · costs 160 GBP · net 39 GBP per year
A simplified model with heating degree days. Frost operation, bypass and air change rates are not assessed.
Compare with the same ventilation
A fair comparison starts from the same necessary air exchange. If the home was previously insufficiently ventilated, a low historical heat consumption is not automatically a suitable basis for comparison.
Enter the airflow, temperature conditions and documented heat recovery. Add the electricity use of the fans, filters and other running costs. A high laboratory value is not the same as the total annual saving. Frost protection, bypass and variation in heat demand can affect the result.
Guide to assessing a system
Use values from the specific quote
Find the airflow and electricity use at the relevant operating point. A system at maximum output does not necessarily describe normal operation in the home. Also find out what installation and later service cost.
Example of recovered heat
At 100 m³ of air per hour and a temperature difference of 20 degrees, the simplified ventilation loss is about 0.68 kWh in one hour. At 80 percent heat recovery, the recovered heat equals about 0.544 kWh before other system factors.
The economic value depends on your heat supply. So convert to avoided purchased energy, and subtract extra electricity and maintenance. The calculation does not assess the placement of the ducts, noise or moisture conditions. Those parts must be included in the planning of the specific system.