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Commercial MVHR: does heat recovery pay back?

Updated 23 October 2026 · SEO Dons Editorial

What is the sum behind heat recovery payback?

Recovered heat in kWh is airflow in cubic metres per second, times 1.21, times the average indoor-outdoor temperature difference, times the exchanger efficiency, times the heating-season hours. The 1.21 comes from the air constants in CIBSE Journal's heat recovery module (specific heat 1.005 kJ per kg K, specific volume 0.83). The net saving is the value of that heat, less the extra fan electricity the exchanger's resistance causes, less extra maintenance. Simple payback is the extra installed cost divided by the net annual saving.

The same module gives the fan part as flow times the additional pressure drop divided by fan efficiency. It cautions that its example is a 24-hour application with low casual gains: in 10-hour buildings with higher occupancy and equipment loads “the savings will not be so dramatic”. A proper study uses binned weather data; this page uses one average temperature difference as a placeholder.

Does the law already require heat recovery?

For most non-residential units, yes. Annex III of the ecodesign regulation says its non-residential requirements include that all bidirectional units shall have a heat recovery system with a thermal by-pass. From 1 January 2018 the minimum thermal efficiency is 73% for every exchanger except run-around systems, which need 68%. A unit that moves air one way only (extract or supply) is a different category with no recovery requirement. So the question for a new balanced unit is usually which exchanger and how much fan power it costs, not whether to fit one.

The regulation itself trades the two. The fan power limit gains an allowance of (efficiency minus 0.73) times 3,000 watts per cubic metre per second, so each extra point of thermal efficiency buys 30 W per m³/s (0.03 W per litre per second) of extra fan power. A unit at 80% earns 210 W per m³/s.

The Energy Technology List sets a higher bar for the products it lists. Its criteria for heat recovery ventilation units need a dry heat recovery efficiency of at least 80%, with a pressure drop of no more than 250 Pa across each side for plate exchangers or 200 Pa for rotating ones, tested to standards such as BS EN 308. Its next technical review is scheduled for 2026-27. Efficiency is measured under dry reference conditions, with balanced flow and a 20 K indoor-outdoor difference, excluding fan-motor heat and internal leakage, so field results differ from rated ones.

What might it save? Two illustrative examples

Prices come from the DESNZ annual report (updated 19 August 2026): its 2025 (provisional) non-domestic averages, including the Climate Change Levy, are 5.3 pence per kWh for gas and 24.3 pence for electricity. Recovered heat is valued three ways: gas with no boiler losses (5.3p), a heat pump at an assumed coefficient of performance of 3 (24.3p divided by 3, or 8.1p), and direct electric heating (24.3p). The exchanger is assumed to add 100 Pa on each side, with a 70% fan efficiency, as in the CIBSE example, which is 286 W per m³/s. The average temperature difference is 10 K and the exchanger is at the 73% minimum. Every other figure below is an assumption.

OfficeSchool
Occupants and rate50 people at 10 l/s4 classrooms of 31 at 5 l/s
Airflow0.50 m³/s0.62 m³/s
Fan hours; heating-season hours2,600; 1,5601,300; 900
Heat recovered6,895 kWh4,932 kWh
Extra fan electricity371 kWh (£90)230 kWh (£56)
Net saving if the heat is gas£275£205
Net saving if a heat pump (COP 3)£468£344
Net saving if direct electric£1,585£1,143

The office rate is the 10 litres per second per person that HSE says many guides recommend. The school rate is the 5 litres per second per person that CIBSE Journal's summary of BB101 reports. Hours are placeholders; a real study uses the timetable.

A saving converts to a ceiling on what the exchanger can cost extra before payback passes a chosen period. These are not installed costs, so compare them with the exchanger and ductwork lines in a quote.

CaseNet saving a year3 years5 years8 years
Office, gas£275£825£1,375£2,200
Office, heat pump£468£1,404£2,340£3,744
School, gas£205£615£1,025£1,640
School, heat pump£344£1,032£1,720£2,752

Moving from 73% to 80% adds about 660 kWh to the office's recovered heat, worth roughly £35 a year at gas prices, so the last few points of efficiency matter far less than hours and the fuel displaced. Fuel prices move: DESNZ's 2023 gas average of 6.4 pence would lift the office's gas-valued heat from £365 to about £441.

What changes the payback most?

  • Hours. The school runs 900 heating-season hours against the office's 1,560, which is why its saving is lower despite a larger airflow. A building ventilated around the clock multiplies the hours again.
  • What the heat replaces. Electricity cost 4.6 times as much per kWh as gas in DESNZ's 2025 figures, so heat recovered from electric heating is worth about 4.6 times as much.
  • Fan power. CIBSE Journal notes the extra fan power is direct electricity and likely to be more costly than the gas heating offset. At the ETL's 250 Pa ceiling per side the fan penalty would be 2.5 times the 100 Pa assumed here.
  • Heat lost to ventilation. The ETL says typically 35% of heated air in commercial buildings is lost through ventilation and air infiltration.
  • Demand control. Lower airflow means less heat to recover. The two measures overlap, as the demand-controlled ventilation guide shows.
  • Summer. The ETL says some units also reduce air conditioning energy by removing heat from incoming air; the MVHR cooling guide works through that.

Which exchanger, and what should a quote state?

The regulation defines three families. A recuperative exchanger transfers heat between air streams without moving parts, such as plate or tubular types. A regenerative exchanger is a rotary wheel, which can also recover moisture. A run-around system links exhaust and supply devices through a heat transfer system, so the two can sit apart. CIBSE Journal's non-residential module says wheels can exceed 80% efficiency but that cross-contamination can occur by carryover and leakage, which matters where exhaust air is contaminated.

  1. Airflow in litres per second and the occupancy it assumes.
  2. Declared thermal efficiency and the test standard behind it.
  3. Pressure drop across each side, or specific fan power, at that airflow.
  4. Hours, temperature difference and fuel price assumed in any saving claimed.
  5. Frost protection, bypass arrangement and the energy each uses.
  6. Filter class and change interval, and how demand control interacts.

Capital costs, and what drives them, are on the commercial ventilation cost guide, and single-room units repeat this sum once per unit in the decentralised MVHR guide. You can send an enquiry through the form on this site.

Sources

Common questions

Is heat recovery worth it in a school?

The school example nets about three-quarters of the office's saving on the same assumptions: a larger airflow, but fewer hours. It can still be the right choice where BB101's criteria push a school to mechanical ventilation, but the break-even premium table shows how tight it is. Check the timetable and the fuel before assuming.

What efficiency should I ask for?

At least the legal minimum, 73% for most exchanger types and 68% for run-around systems, and ask for the test standard. The ETL's 80% is a useful benchmark. Ask for pressure drop or fan power alongside it, because the regulation allows 30 W per m3/s more fan power for each extra point of efficiency.

Does a heat pump change the payback?

Yes, because it changes what the recovered heat is worth. With an assumed coefficient of performance of 3, a kWh of heat costs 8.1 pence against 5.3 pence for gas on DESNZ's 2025 averages, so the same recovered heat is worth about half as much again. The coefficient is an assumption, so use the figure from the heat pump's data.

Does heat recovery help in summer?

It can. When the outdoor air is warmer than the extract air, the exchanger pre-cools the incoming air, and the ETL says some units can reduce air conditioning energy. It does not create cooling by itself, as the MVHR cooling guide explains.

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