A run-around coil system uses two coils, one in the exhaust and one in the supply, joined by a piped loop of water or brine. A pump moves the fluid: it warms in the exhaust coil and gives up heat in the supply coil. There is no path for air to mix between streams.
When it is the only option
- Streams are far apart: exhaust and intake may be on different sides of a building; a pipe bridges them.
- Strict separation: hospitals, labs and kitchens where any carryover is unacceptable.
- Retrofit: no need to route both ducts through one core.
Trade-offs
Effectiveness is modest, typically 40% to 65%, because the fluid loop adds thermal resistance and a pump uses energy. For adjacent streams, a direct plate or heat-pipe unit recovers more. But when distance or separation rules out a direct exchanger, run-around is the pragmatic choice.
Pair it with the guidance in our efficiency article and sizing guide.
Specifying a unit for your project?
EN159 builds plate, rotary, heat-pipe and counterflow air-to-air exchangers. Send airflow (m3/h), inlet temperatures and available space and we will size it.
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