Heat recovery ventilation

pragmatic

Hi is anyone using HRV?

It looks quite intriguing,  there are a few kits on Amazon for a few hundred pounds but they seem to go up to the multi £k mark.

Anyone have experience with them?  Any idea what sort of real world heating/energy saving or lifestyle benefit they bring?

For anyone scratching their head, this is what I've read, there is a central box that takes a number of vents in (e.g. kitchen, bathroom) and then vents out (living/bedroom), it takes the warm air from the kitchen and bathroom and pumps that outside while pumping in cold air from outside.  The magic as it were is that there is a heat exchanger in the middle which uses the warmth from the inside air to heat up the incoming colder air.  I've seen rates from 60%  to 85% for the efficiency of the system.

Additional reported benefits are that it stops mold growth etc in bathrooms and kitchens by constantly whicking away steam/moisture while also supplying clean dry air to the incoming vents. I'm assuming unless you live somewhere polluted the constant refreshing of air from the outside would have other health benefits.

Apparently you are meant to completely refresh the air in a house/flat etc every 2 hours, not sure how many achieve that though!

neilball

I've got a Vent Axia AirMinder unit that I fitted when I built my house 8 years ago. It certainly keeps the house feeling very fresh, it never feels stuffy. And bathrooms still get steamy when lots of showers/baths are running but it does clear quickly. There is no annoying fan noise (I find standard extract fans very intrusive know!), and when the incoming fresh air fan shuts down in the coldest weather (to prevent freezing up the heat exchanger) you certainly notice a difference in the house after a few hours. We also do not need or have any trickle vents in any windows because of the continuous ventilation.

While it does save energy by reducing the effects of cold incoming air it still delivers colder air into rooms in winter, although several degrees higher than the air would have otherwise have been. And the duct sizes used also mean it will not deliver enough air volume to be thought of capable moving heat around the house (although as I say the incoming fresh air in winter is cool so is still effectively cooling the rooms down rather than moving any heat around). If you wanted to use the system for background heating or cooling with additional heaters/cooling in the main supply duct then larger ducts and bigger fans would be needed to move the required air volumes and achieve the heat/cooling capacity to make any real difference in the rooms. And without motorised volume control dampers on the feeds to each room it would be impossible to control a system using these heating/cooling sources.

If you want a system to be quiet in operation you need to use smooth bore ducting and restrict the use of corrugated flexible duct as much as possible. And the ducts need to be well sealed, so don't think about using duct tape which will start to peel off as the adhesive dries out after a few years.

A well designed main unit with summer bypass damper and low energy fans is probably going to be around £1k, and then you have the costs of the ducting and installation to add to this. So it is not cheap, and a bit of a luxury item in a similar way to a central vacuum system. However I am pleased I fitted it and would do so again should I build another house.