An air compressor turns almost all the electricity it uses into heat. On a screw compressor, that heat leaves by a well-defined path, and part of it can be used to heat a room or preheat water. Heat recovery is not an accessory you add from a catalogue: it is an installation project, studied site by site with our technicians and your installers.
Where the heat comes from
This is a matter of conservation of energy, a law of physics. The electricity going into the motor does not disappear: it compresses the air, and compression heats that air. Only a small share leaves as energy stored in the compressed air. The rest becomes heat that has to be removed.
In an oil-injected screw compressor, the oil injected into the airend absorbs the heat of compression. It then flows through a cooler, where the machine's fan passes the heat to the room air. The compressed air also goes through a cooler: on our screw compressors, it leaves at no more than 15 °C above ambient temperature. The motor gives off some heat as well.
Our S, K, L and M series compressors are air-cooled. All of that heat therefore leaves in a single stream: the hot air blown out by the fan.
Two ways to recover it
1. Through hot air. A duct is fitted to the machine's hot air outlet. A damper sends the air into the workshop in winter and outside in summer. This is the simplest solution on an air-cooled compressor. It needs a short duct with few bends: a duct that is too long holds back the fan, and you then need to ask our technicians whether a booster fan is required.
2. Through water. A heat exchanger on the oil circuit passes the heat to a water circuit, to preheat washing water, hot water or a heating return. This is a heavier job, carried out by a professional. The exchanger must be designed so that the compressor always stays cooled, even when nobody uses the heat: the machine comes before the recovery. Any work on the oil circuit is done with our technicians' agreement.
| Recovery through air | Recovery through water | |
|---|---|---|
| Use of the heat | Heating a workshop or a neighbouring room | Hot water, washing, preheating, process |
| What to install | Duct, damper, fresh air inlet | Exchanger on the oil circuit, connection to the water circuit |
| Useful season | Mainly winter | All year, if there is a need for hot water |
| Watch point | Duct length, venting outside in summer | Guaranteed cooling of the compressor |
How much heat, an order of magnitude
Since almost all the electricity becomes heat, the energy used gives the maximum heat available. Take the motor power multiplied by the hours running on load, as in our guide on compressor energy cost. It is a ceiling, not a promise.
Example with an S 150, a 15 kW screw compressor running 2,000 hours a year on load:
- 15 kW × 2,000 h = about 30,000 kWh of electricity a year.
- The heat produced is in the same range: at most, about 30,000 kWh a year.
- The share actually recovered is lower. It depends on the method, on losses in the duct or exchanger, and above all on whether heat is needed while the machine is running.
The same calculation for the S series, still at 2,000 hours on load:
| Model | Power | Heat produced at most, per year |
|---|---|---|
| S 55 | 5.5 kW | about 11,000 kWh |
| S 75 | 7.5 kW | about 15,000 kWh |
| S 110 | 11 kW | about 22,000 kWh |
| S 150 | 15 kW | about 30,000 kWh |
| S 220 PM | 22 kW | about 44,000 kWh |
On our permanent magnet motor compressors, the speed follows the air demand. When the workshop uses less, the machine slows down and produces less heat. The available heat therefore follows your air production, not the motor rating plate.
When the project makes sense
- The compressor runs a lot. No air produced, no heat. A machine that runs a few hours a week does not justify an installation.
- The heat is needed at the same time. Heating an occupied workshop while the machine runs, yes. Heating an empty room at night while the compressor is off, no.
- The use is close by. The longer the duct or water pipe, the more heat you lose and the more the installation costs.
- Cooling stays the priority. In summer, or when the heat is not used, it must be able to go outside without hindering the machine. A compressor that draws in its own hot air ends up tripping: see our article on compressor overheating.
How to move forward
- Estimate the energy involved. The electricity cost calculator gives the kWh your compressor uses each year. That is also the maximum order of magnitude of the heat produced.
- List the heat needs around the compressor room: heating, hot water, process, with their hours.
- Have the installation studied. Our compressed air audit looks at production, control and cooling, and checks whether heat recovery is relevant on your site.
For a new compressor, the S series machines, up to the 22 kW S 220 PM, lend themselves well to duct recovery. Describe your project in a quote request, with a rough plan of the room and your heat needs: we study it with you, case by case.