Compressor heat recovery - how much energy can you reuse?
A screw compressor turns almost all of the electrical power it draws into heat. This guide explains how much of it is reusable, which air and water systems exist, and when heat recovery pays off.
Browse compressorsHow much waste heat does a screw compressor give off?
A screw compressor produces no thermodynamic net work: roughly 100 % of the electrical power drawn is converted into heat. On oil-injected machines, typically 72 to 94 % of that can be recovered as usable heat.
The largest share is carried by the compressor oil, which absorbs the compression heat and releases it through the oil cooler. A smaller part sits in the compressed air (aftercooler), and the rest is lost as radiation and motor losses. Only about 2 to 5 % actually remains as pressure energy in the compressed air.
Air or water system - which fits when?
There are two basic principles: direct warm-air ducting and water heat recovery via a heat exchanger. The choice depends on whether you want to heat rooms or produce hot water and process heat.
Air ducting is the simplest and cheapest option: the heat picked up by the cooling airflow is fed straight into a hall through a duct with a damper, raising the supply air temperature by around 20 to 25 °C. In summer the damper is opened to the outside.
The water system couples a plate heat exchanger into the oil circuit and delivers hot water at typically 60 to 70 °C, and up to 90 °C with special exchangers. This can feed domestic hot water, heating return lines or process baths - independent of where the compressor stands.
- Air system: low investment, ideal for hall heating in winter, only worthwhile with short duct runs.
- Water system: higher investment but usable year-round and transportable over piping to distant loads.
- Hot water at 60‑70 °C covers showers, cleaning and boiler feed-water pre-heating.
- Process heat up to 90 °C for baths, drying and pre-heating stages in production.
- Combined units send air into the hall in winter and water into a buffer tank in summer.
When does heat recovery pay off?
Profitability stands or falls with the operating hours and a matching heat consumer. The longer the compressor runs under load and the closer the load, the faster the system pays back - often within one to three years.
Example: a 30 kW compressor with 4000 load hours per year releases around 108,000 kWh of heat at 90 % recovery. At a gas price of about 0.10 EUR/kWh that equals annual savings in the order of 10,000 EUR - while retrofit kits often cost far less.
Frequently asked questions
What percentage of compressor power is usable heat?
On oil-injected screw compressors, typically 72 to 94 % of the drive power drawn can be recovered as heat. The largest share comes from the oil cooling circuit.
What water temperature does heat recovery provide?
Standard heat exchangers in the oil circuit reach 60 to 70 °C flow temperature. Special high-temperature exchangers allow up to 90 °C, enough for many process baths.
Is heat recovery worth it on small compressors?
Yes, as soon as there is a nearby heat consumer and sufficient load hours. Even a few kW of drive power can cover hot water or a workshop heater.
Does heat recovery reduce compressed-air output?
No. The heat arises as loss energy anyway and would otherwise be dumped to the surroundings unused. Air volume and final pressure stay unchanged.
Want to reuse your compressor's waste heat?
We advise on air and water heat recovery systems and supply matching compressors, heat exchangers and air treatment.
High yield
Up to 94 % of drive power available as usable heat.
Fast payback
Typically one to three years with a good heat demand.
Right systems
Air and water solutions for heating and process heat.
Expert advice
We size heat exchangers and buffer tanks correctly.