Most buildings already exhaust warm (or cool) air straight to atmosphere. A retrofit adds an air-to-air core to that existing exhaust — often the fastest energy win in the building, because the ductwork and fans already exist. The trick is justifying it with a believable ROI.
Retrofit steps
- Measure the duty: exhaust airflow, temperatures, hours/year. Start with the savings calculator.
- Pick the location: where do supply and exhaust run close together? If far apart, use a run-around coil.
- Choose type: plate where streams are clean; wheel where you also want moisture control; heat pipe where cross-contamination is forbidden.
- Check the fan: added ΔP may need a bigger motor — model it (see pressure drop).
- Confirm frost: cold-climate exhaust needs frost control.
- Run the payback: with the payback tool on delivered cost.
Typical savings and payback
For a continuously ventilated industrial or commercial building, recovered energy is commonly 50–80% of the exhaust sensible load, worth thousands of dollars a year per 1,000 m³/h at typical ΔT. Payback is usually 1–3 years for continuous duty, 3–5 for part-time. See real application numbers in industrial waste heat recovery and retrofit of existing buildings.
Traps that sink retrofits
- Counting fan power twice: net saving = recovered minus the extra fan energy from added ΔP.
- Ignoring the exhaust profile: a greasy or corrosive exhaust needs the right core or it fouls in a season.
- No maintenance plan: a retrofit with no filter access loses recovery fast.
- Wrong stream balance: if make-up air ≠ exhaust, recovery is capped.
When a retrofit is NOT worth it
Very low exhaust hours, tiny ΔT, or an exhaust you must not recirculate any part of (some lab/process streams) — there the case is weak and a run-around coil or no recovery may be correct.
Thinking about a retrofit?
Send your exhaust airflow, temperature and hours — we will size a core and give you a payback range.
Request a quote