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MVHR - Most Frequently Asked Questions

We get dozens of queries from self-builders and architects who want to know if MVHR is the right vent strategy for them. Here's a list of the most frequently ask questions that we’ve come across.

FAQ - Is MVHR The Right Vent Strategy For You

By Llyr Davies, Residential Business Development Manager October 2014

1. How does an MVHR system work?

In wet rooms, such as kitchens, bathrooms, W.C’s and utility rooms and extract points are installed to remove the warm, moist air. Before it is exhausted to outside, the extracted air is used to temper the incoming air into the building via a heat-exchange block within the unit. The heat exchanger can transfer up to 92% of the heat recovered into the fresh incoming air. The fresh, filtered, pre-warmed air is then supplied into the habitable rooms such as the bedrooms and living room.

2. How are the ventilation rates calculated?

Typically, the minimum ventilation rate is calculated by multiplying the total internal floor area by 0.3 l/s/m². The boost rate is calculated by assigning the following vent rates to each wet room and then adding them together. (kitchen 13l/s, bathroom 8l/s, utility 8l/s, WC 6l/s)

3. What to do if my home gets too warm?

During the summer months, there is a summer bypass system. This means that the intake air will not be tempered as it is diverted around the heat exchange block. This can help in reducing the indoor temperature.

4. Can I leave my windows open?

MVHR units can run with the windows open. However, this will make the unit less efficient during the winter months.

5. How will it work with my heating system?

MVHR systems are designed to ventilate your home; it does not heat your home. The two operate entirely independently. However, the benefit is that you do not lose the heat you’ve paid to be generated as you would with a standard ventilation system, as the MVHR system will recover up to 95% of this heat energy

6. Is much maintenance needed?

There is very little maintenance with our MVHR units. We recommend ventilation servicing and that you check your unit filters annually. The filters can either be cleaned or replaced. However, this will depend on the environment in which you live and how clean the air in your home is.

7. How is the system controlled?

The minimum requirement for controlling the MVHR system would be to have a manual boost switch for each wet room. But the unit can also be controlled via humidistats, PIR sensors and wireless switches.

8. How long is the payback period?

Nuaire’s MVHR units run on an average of 15p per day. Most Nuaire MVHR units have a payback period of 7-10 years. This can vary depending on environmental factors and the airtightness of your home.

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