Location of MHRV

creedp

I will be installing a MHRV system in a new build shortly and intend to locate it in the attic which is not insulated. However, I was reading some material from a certain supplier which stated you should never locate the heat recovery unit in a cold uninsulated part of house (e.g. attic) without installing it with an additional insulation jacket as this would result in heat loss and excessive condensation.

This is the first time I have come across this point as all the other suppliers advised the unit should be installed in the attic without making reference to this additional insulation jacket.

I would like to hear others views on this issue and if units installing in attics included this additional insulation.

Thanks

soldsold

Definitely you need to insulate it. You can buy an insulation kit from the hrv supplier or probably cheaper to diy, make sure the insulation is securely fitted and use plenty. Otherwise the pipework will lose a lot of heat and you will get condensation on the unit and pipework. Be careful to keep the ducts airtight at all joints and where they break through the airtight layer in the house. Probably easier for routing pipes to have it in the attic but mine is inside the heated zone to avoid the above issues

creedp

Thanks Soldsold

Just to confirm are you saying that the Unit itself must be insulated as well as the duct work - I was aware that the duct work within the attic has to be insulated but I am unsure about the Unit itself. Is it possible to competely seal the Unit? What about the motors within the unit - do they need ventilation? Is there a danger or over-heating? Also will it be difficult to maintain the filters if the Unit is sealed with insulation?

If not located in attic what are the alternatives for a Unit sufficient for an 2800 sq ft house. How will the ductwork be accommodated bearing in mind that it is recommended to use 6"/150mm circular ducting? I would have thought that this would be very bulky to conceal within the house itself. I can't imagine how I could manage this in my build which has block internal walls. Am I missing something?

Thanks

slavetothegrind

Check the mounting instructions also, i would be careful to mount it so as to avoid noise transmission by vibration.

Soldsold might advise on his?

soldsold

Sorry I should have been clear - you need to keep the unit and duct as airtight as possible. You will only have to insulate the unit if its not done as standard, the one in my place is moulded from expanded polystyrene so would not be an issue. I would follow the advice of the supplier though.


The unit should be able to fit in the eaves, ductwork can be put through wardrobes etc if 150mm diameter, or you can use 60 x 200mm rectangular ducts on some units, apparently the same performance as 150mm round duct.

On mounting the unit the supplier should specify the wall that is needed ie the density of the wall. The ones I have seen running dont vibrate much, you could look at using rubber washers on the screws if you wanted to. Mounting to a block wall will be fine, best to check with supplier if mounting to timberframe but I cant see it as an issue, maybe backing with plywood or OSB might be needed.

creedp

I was speaking with a MHRV installer and he said he normally uses a 5" flexible insulated ducting in a cold attic space. When I asked him about the resistance problems associated with flexible ducting he said that the increased 5" diameter significantly reduces this issue. An alternative he uses is a foam based rigid type duct which has a superior insulating value and is only marginally more expensive.

I had though that the rigid type ducting was pvc based and insulated externally. Has anyone come across this foam based ducting and have any opinions on it for use in a cold attic?

Thanks

beyondpassive

Creepd,
Another issue to consider in locating the unit, you will need to get access to the unit to clean filters, some people use a hoover to clean the filter, 3 or four ties a year. In the first few months following completion, there can be a lot of dust in the filters and access is needed more frequently. In summer access is also needed to enable the summer bypass. I still cant figure it out on the paul systems.

CJhaughey

You can also get HRV units that sit on the floor like a fridge.
Mine is like that and the door simply opens to enable me to service the filters or even just check what condition they are in.
The problem with attic mounted units is out of sight is out of mind and having to crawl into an attic is a bit of a hassle.

CJhaughey

CJhaughey wrote: »

You can also get HRV units that sit on the floor like a fridge.

The problem with attic mounted units is out of sight is out of mind and having to crawl into an attic is a bit of a hassle.

Yes, mine's in the attic, if I was to do this again I'd definitaly place it within the envelope of the house. Somewhere like the hot press for example.