DCV Demand Control Ventilation


New Member
I have a number of manual extraction fans in the bathrooms, there is quite a draft comes from them.

I'm currently looking at improving air tightness of house , would something like DCV help the situation?

My understanding is the DCV only opens when it detects occupancy , humidity etc so I'm assuming they would be closed at other times and hence keeping house more air tight ?


Registered User
The typical setup for a DCV system is extractor fans in the bathrooms and sometimes kitchens along with air inlets in the other rooms, the idea being the extractors expel stale air from those rooms and fresh air is drawn in through the rooms with inlets. Typically you need a 1-2cm clear gap under your internal doors so that air can move throughout the house.
The extractor fans tend to run constantly at a slow speed and then increase speed when they detect high humidity or some have a boost function to remove smells. The inlets are typically closed and then open when there is humidity in the room.

The humidity sensitive extractor fans are very good, we have this model: https://www.greentherm.ie/product/intellivent-intelligient-extract-technology and then we have aereco inlet vents in the bedrooms and living rooms. In the main kitchen/dining/living room we just have a typical wall vent as this room is high-occupancy and with cooking etc we didn't think it worthwhile the extra expense of a DCV inlet.

It should be noted that when the DCV inlets are "closed" they're not airtight, they just restrict flow somewhat. They are intended to be used with the extractors so that air is sucked in through them.

If you are looking to prevent air from being blown in through your extractor fan, that's not quite the same issue that DCV is intended for. You can look at getting a draught proof cowl for the exterior of the vent which should solve that issue at significantly less expense.

However you should also consider that when your extractor fan is running, where does the fresh air supply to the bathroom come from? This could just be to open the window while showering etc but an extractor with no fresh air supply will not do much good.