MVHR FAQs

Q. Why do I need MVHR?

A. The air in a home contains moisture, odours, carbon dioxide and VOCs (volatile organic compounds), and other potentially harmful contaminants.

An MVHR system continually removes this 'stale' air and replaces it with fresh, filtered air at around room temperature.

This provides a superior environment for your health and also saves on heating bills, because now you do not need to let in cold air to keep the home environment healthy.

There is a long list of benefits and reasons to get MVHR, scroll to the end of the page for more.

Q. Is MVHR a heating system?

A. Not as such, no. Standard MVHR does not heat a home.

It recovers the heat from the stale air it sends outside - heat that would be lost if you had trickle vents / intermittent fans (the norm for ventilating UK homes).
Adding extra heat to the air can be designed in, however this is only suitable for homes with high levels of insulation and a low airtightness score (below 1 ACH @ 50Pa).

Q. How loud is it?

A. A properly designed system will be effectively inaudible in all rooms except the room in which the MVHR unit is located. The kitchen grille will typically be under 25dB(A) and living spaces typically under 20dB(A), well under building regs limits. New owners are often delighted to find they cannot hear anything from the air valves.

Q. Does MVHR cure damp and mold?

A. If the root cause of mold and damp is water leaking into the home via the building fabric - from damaged roofs, guttering, pointing etc, then clearly MVHR cannot solve that problem.

However, the majority of mold and damp occurs not from leaks, but due to an environment in which there is insufficient ventilation, because humid air is not adequately moved out, and may condense on cold walls, ceilings, windows etc. A humid, stagnant environment is ideal for mold growth.

In this case, MVHR will often eradicate the issue because it is continually changing the air in the house (usually 0.3 - 0.4 air changes per hour. Furthermore, while up to 92% of the heat will be recovered, not all of of the moisture will be - some of it is drained away. Therefore MVHR has a slightly dehumidifying effect on the air in the home.

Personal anecdote from our Director Paul - "Following the installation of MVHR in my house, the average relative humidity dropped from 70% to 52%, and visual proof of this is I no longer wake up to condensation on my (double glazed) windows."
And remember, less humid air is easier to heat!

Q. Can my MVHR unit go in the loft?

A. Yes, albeit with some caveats.

If you have a 'warm loft' (insulation at or near the rafters) then no problem.

If you have a 'cold loft' (insulation at the loft floor), the ducting must be insulated and ideally the unit enclosed within an insulated cupboard.

In general, it is better to make provision for the unit and ducting within the thermal envelope.

Q. Where does the ducting go?

A. A good designer will look to run ducts within floor joists, stud walls and any useful voids you may have. It will be their aim to not need any boxing in, bulkheads, lowered ceilings etc. to hide ducts, though sometimes these are unavoidable.

For those who like the industrial look, the odd section of exposed spiral (galvanized steel) ducting can look appealing.

Q. What are the running costs?

A. The actual figure is directly related to the fan speed, whether any pre-heating element is working, and more. We will give some figures to give you an idea.

Typically a unit will run at 20-40 watts, increasing to 30-60 watts at boost. If we average that at 40 watts for the year, this equates to around £88 per year or £7.33 per month (based on 25p per kWh).

You will need to replace the pair of filters twice per year, average cost £90.

A total of under £178 per year / £15 per month.

This is money you probably would have spent ventilating in the standard way (trickle vents, intermittent fans).

Q. Are you qualified?

A. Yes, we hold both NICEIC and BPEC qualifications for designing, installing and commissioning MVHR systems. In terms of experience, we have designed hundreds and installed around sixty full systems across previous employment and as Heat Recovery UK.

Q. What are the benefits of MVHR?

A. Quite a few, here are the main ones!

- Better sleep through reduced CO2 air concentration
- Significant reduction in heat losses meaning lower energy bills

- Total elimination (likely) of condensation and mold

- Relief for allergy and asthma sufferers

- Continuous fresh air without draughts

- Removal of cooking and pet odours

- Outside noise reduction and greater security

- Passive cooling through summer bypass

- Removal of VOCs (volatile organic compounds)

- Faster indoor clothes drying

- More even temperature across the whole house