MVHR Frequently Asked Questions - Information Hub Green Building Store


Solar space at Denby Dale Passivhaus

Answers to frequently asked questions by building residents & occupiers

MVHR (mechanical ventilation with heat recovery) supplies fresh air to all habitable rooms. It also removes moist stale air, reusing the heat to pre-heat the fresh air entering the building.

Can I open the windows?

Yes you can and the MVHR system will continue to operate in the background. However the efficiency of the MVHR will usually be slightly reduced – affecting its ability to keep the building warm in winter and cool in summer. The exception to this is when windows are opened for summer purging (see below).

Does the system run 24/7 for 365 days of the year?

It is set for automatic use all year round so you do not have to adjust any settings. However you may want to over-ride the automatic system on some occasions (see below).

How much electricity does it use?

Green Building Store domestic MVHR systems typically have 2 very small motors which push the air through your system. A unit like Focus 200 uses 22 Watts. This is similar to having a low energy light bulb on in your home, costing around 10p per day.

What will happen if the electricity supply is cut off?

You may start to feel that the air is becoming a little stale, but do not worry you will not suffocate! In the unlikely event that it happens whilst you are asleep, then your bedroom might seem a bit stuffy in the morning.

Is it noisy?

Supply and extract ducts in MVHR system design

We design MVHR systems to have minimal noise impacts and they should run almost silently. It is important not to block any of the air vents as this will put the whole system out of balance.

What maintenance do I need to do?

Apart from keeping all the air vents clear and clean, the only maintenance is periodic filter changes. There are several filters which need to be changed to keep the air flowing properly. How frequently depends on where you live and how clean the air is. The filters keep your air clean, but are also needed to keep the system working properly. The kitchen extract filter may need changing/ cleaning more often than the others. Normally filters need to be changed every 3-6 months.

Will it heat my house?

MVHR will re-use the heat which already exists in your home produced by occupants and electrical equipment. Some systems can be designed to have an additional in line heater, to heat supply air, but this can only provide a small amount of heating.

Can I dry clothes?

Yes, clothes dry very well indoors and create some moisture which is beneficial. You also might like to grow plants.

What is summer purging?

If you experience unusually high outdoor temperatures and your home is too hot, it is recommended that you ‘summer purge’. (This is standard practice in hot climates).

Open windows during the night so that the cool air can enter and reduce indoor temperatures.
During the hot day close your windows and increase the fan speed on your control panel to increase ventilation.

Can I boost the fan whilst cooking?

Yes. Just go to your control panel and touch the boost button. It will stay on for a pre determined time (usually 30 minutes), and your system will then revert to normal operation. You may have an additional boost button in your kitchen or bathroom which will have the same function.

What do I do when go on holidays?

You can reduce the ventilation while you are away. Simply go to your control panel and reduce the fan speed to the minimum. When you return home just return to the standard setting and your system with return to normal operation.

What should I do if there are more people in the house or if there is a party?

You can increase the ventilation for ‘high occupancy’. Simply go to your control panel and increase the fan speed. When people have left, return to the normal ventilation setting, which will keep the air feeling fresh.

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