Green Building Forum - insulating a mvhr unit it the loft

insulating a mvhr unit it the loft

jms452 — Sat, 27 Mar 2021 15:20:02 +0000

Our current loft mounted MVHR unit screws onto the ceiling joists and is buried under loft insulation keeping it nicely insulated.

http://www.nuaire.info/IandM/671438.pdf

However, it is 10 years old, the fans were replaced under warranty after about 4 years when the engineer told us that they no longer use that type of fan in the newer units due to poor lifetime. One of the fans is starting to go again so I'm looking at options. It is also rather primitive in that you need to take it apart to change the filters which is a bit of a pain.

Most of the current units (e.g. Vent-Axia 438222 Sentinel Kinetic B) have neat easy change filters and talk about loft mounting but they are effectively wall mount units and our loft is 'cold'. As the units are not particularly well insulated I'm contemplating building a PIR box around such a unit in the loft but this will make access a pain.

Any thoughts - common sense tells me there must be a decent accessible + insulated MVHR out there but I'm not seeing it.

insulating a mvhr unit it the loft

Peter_in_Hungary — Sat, 27 Mar 2021 18:05:19 +0000

Are the new type fans compatible (or adaptable) with the old units If so it may be easier and cheaper to put new style fans in your unit.

insulating a mvhr unit it the loft

revor — Sat, 27 Mar 2021 18:53:40 +0000

I have a Titon unit which is basically an engineered polystyrene box housing all the gubbins, so is insulated and quiet except on boost. It is quite old now and may no longer be available. But have look see.
Ours is wall mounted but it is light enough and could easily be hung on a frame. The condensate drain is on the bottom so could not be placed on any surface.You have to take the front off to change the filters 5 min job once a year. It is in a plant/utility room.

insulating a mvhr unit it the loft

djh — Sat, 27 Mar 2021 20:05:32 +0000

Posted By: jms452I'm contemplating building a PIR box around such a unit in the loft but this will make access a pain

Can you not build a box where the 'lid' of the box is the 'front' of the MVHR that you need to access for the filters? Then unclipping a couple of hook and eye fasteners and lifting the lid out of the way wouldn't take long. Or is your situation more complicated? I'd have expected aligning the new ducts with the old ducts might be more complicated.

insulating a mvhr unit it the loft

jms452 — Sat, 27 Mar 2021 20:21:46 +0000

Posted By: Peter_in_HungaryAre the new type fans compatible (or adaptable) with the old units If so it may be easier and cheaper to put new style fans in your unit.

I'm time poor these days and trying to avoid having to build my own unit, would also be nice to be able to change the filters cleanly and easily.

Posted By: revorI have a Titon unit which is basically an engineered polystyrene box housing all the gubbins, so is insulated and quiet except on boost. It is quite old now and may no longer be available. But have look see.

They have pretty good specs but I wouldn't be happy with 1cm on polystyrene anywhere else on the house.

Posted By: djhCan you not build a box where the 'lid' of the box is the 'front' of the MVHR that you need to access for the filters? Then unclipping a couple of hook and eye fasteners and lifting the lid out of the way wouldn't take long. Or is your situation more complicated?

Getting a nice seal is the bit that becomes involved.

I can do it all but I'm getting lazy and was hoping a '2 day' job rather than a 'week job'

insulating a mvhr unit it the loft

djh — Sat, 27 Mar 2021 20:34:52 +0000

Posted By: jms452Getting a nice seal is the bit that becomes involved.

Ah, you're more of a perfectionist than me. Stick a bunch of window draught strip around the edge, would do it for me. It doesn't have to be perfect, I don't think. The units should be plausibly well-insulated anyway.

insulating a mvhr unit it the loft

tony — Sat, 27 Mar 2021 21:00:52 +0000

The unit will be half warm, house air temperature and half cold (outdoor temperature) less fan heat losses

Complex problem

insulating a mvhr unit it the loft

jms452 — Sun, 28 Mar 2021 09:54:48 +0100

@revor - How would you report on the Titon?
How long have you ran it for?
Breakages & spares?

cheers

J

insulating a mvhr unit it the loft

djh — Sun, 28 Mar 2021 11:54:58 +0100

Posted By: tonyThe unit will be half warm, house air temperature and half cold (outdoor temperature) less fan heat losses

That's why

Posted By: djhThe units should be plausibly well-insulated anyway.

insulating a mvhr unit it the loft

an02ew — Fri, 02 Apr 2021 21:00:15 +0100

IMO they just shouldnâ€™t be mounted in an uninsulated space. But as you have already crossed that bridge then a purpose built celotex (or other) box would be a must. Shouldn't take long and you could foam any gaps. Laminating up the layers off-setting joins to really get a good seal. There isnâ€™t any unit on the market that will copy with subzero temps without losing all its saved energy or worse becoming a dripping mess of condensation.

insulating a mvhr unit it the loft

revor — Sat, 03 Apr 2021 14:03:21 +0100

@jms452. I have had my unit since 2012 but was not commissioned for some time as we needed it for positioning duct runs which we were doing during the build and house is still not fully balanced. We do not use it all of the time. It is on if we are showering (on boost) cooking (we have a recirculating extractor the MHVR then picks up the exhaust in the kitchen). Generally do not use at night in the winter as not much point drawing in cold air but it is used at night if the house got a bit too warm during the day. It is a fairly large property and only 2 of us so we do not have issues with condensation that would need us to run unit full time. So having set out the way it is used to put usage into context we have not had any issues with it at all (hope not tempting fate). It was easy to set up clear instructions. Filters are readily available from Titon I did look for an alternative supply but could not find a supplier of the size required. Last time I bought a box of 12 sets I think, they come with a time in use sticker which helps keep track of when time to change. I usually change them every 12 months.

insulating a mvhr unit it the loft

djh — Sat, 03 Apr 2021 16:47:11 +0100

Posted By: an02ewIMO they just shouldnâ€™t be mounted in an uninsulated space. But as you have already crossed that bridge then a purpose built celotex (or other) box would be a must. Shouldn't take long and you could foam any gaps. Laminating up the layers off-setting joins to really get a good seal. There isnâ€™t any unit on the market that will copy with subzero temps without losing all its saved energy or worse becoming a dripping mess of condensation.

Do you have any references to back up your opinion?

As Tony says, an MVHR is full of air half at room temperature and half at outside temperature. The unit itself is insulated to prevent heat loss or gain in either circumstance, and whichever ducts are in the 'wrong' zone clearly need to be well insulated. But beyond that, and ease of access to change filters etc, I don't know of any reason it can't be mounted somewhere colder than normal. Note that we are talking about internal spaces such as lofts or garages or externally-accessed cupboards and these will not normally freeze.

GBS seems to agree: https://www.greenbuildingstore.co.uk/mvhr-dos-donts-where-to-locate-mvhr-unit/

insulating a mvhr unit it the loft

an02ew — Sat, 03 Apr 2021 20:57:39 +0100

Iâ€™m not surprised GBS advocate the use in uninsulated areas, itâ€™s not good business to advise against install in cold zones.

As for installation in cold areas, so long as ducting and distributing boxes are well and meticulously insulated and the unit is has additional insulation too then you should be ok. But I have seen installs were a bit of loft roll is tucked haphazardly around duct and nothing around distribution boxes. Turning it into MVNHR( no heat recovery) which is just a waste on money. And seen condensation on the external surface of the fan unit.

Unrelated, Iâ€™ve also seen the intake vent completely frozen solid. Cold foggy conditions and a modern stainless grill type vent, resulted in the incoming moist air condensating on the cold metal grill and freezing over completely.

insulating a mvhr unit it the loft

djh — Sun, 04 Apr 2021 09:27:12 +0100

Posted By: an02ewAs for installation in cold areas, so long as ducting and distributing boxes are well and meticulously insulated and the unit is has additional insulation too then you should be ok. But I have seen installs were a bit of loft roll is tucked haphazardly around duct and nothing around distribution boxes. Turning it into MVNHR( no heat recovery) which is just a waste on money. And seen condensation on the external surface of the fan unit.

That's all true but applies equally to the intake and exhaust ducts when the unit is installed in a warm area. In fact more so, since they're liable to condensation on their surface. But again, why do you think the situation is any different for the unit itself whether it is in a warm or cold area?

insulating a mvhr unit it the loft

Nick Parsons — Sun, 04 Apr 2021 09:53:23 +0100

As regards GBS and MVHR I can only confirm that, on the job I was involved with, they were very clear that the unit should be within the house itself (we had originally intended to build it an insulated 'house' within the cold loft). And I don't think the link implies wholehearted support for installation outside the heated envelope:

''....Despite our reservations, in some cases we have sited MVHR units in lofts, commonly in retrofits and smaller projects.''

insulating a mvhr unit it the loft

an02ew — Sun, 04 Apr 2021 14:37:55 +0100

Posted By: djhBut again, why do you think the situation is any different for the unit itself whether it is in a warm or cold area?

If your looking for your MVHR to recover anywhere near its quoted efficiency figures then itâ€™s needs to be within the thermal envelope of the building. That includes the ducting and distributions. Forget the summer bypass when youâ€™ve got the system in a 40+ degree loft with a bit loft roll stuff around it.

If your spending 2k plus on MVHR and itâ€™s in the loft then spend another Â£500 and seriously insulate fastidiously otherwise your wasting the original 2k

insulating a mvhr unit it the loft

djh — Sun, 04 Apr 2021 15:17:55 +0100

Yes you can repeat your assertion as much as you like, but please show the evidence. You may well be right but there's no particular reason I should believe you unless you offer some backup.

And again, specifically the MVHR unit. The ducts and distribution boxes etc are obvious.

insulating a mvhr unit it the loft

an02ew — Sun, 04 Apr 2021 19:21:17 +0100

Believe what you like. And mount you MVHR were you like, itâ€™s your money you can poke it down whatever drain you like too.
Ive commissioned plenty of systems and Iâ€™ve seen some shocking installs and condensation on the outer casing.

insulating a mvhr unit it the loft

an02ew — Sun, 04 Apr 2021 19:57:01 +0100

All Iâ€™m saying is a devise that tenuously removes heat from outgoing air needs all the help it can get.

insulating a mvhr unit it the loft

jms452 — Sun, 04 Apr 2021 20:34:25 +0100

Thanks for the thoughts all.

Unit is in the loft and the last one was insulated with 50mm PIR (plus token insulation of the unit). All the warm duct runs are under at least 200mm of loft insulation.

As Tony says half is warm and half cold - In that case I might get improved performance if insulation is closely pressed onto the unit?

Andrew I'd much prefer to have it internally and appreciate your experience on this - looks like some meticulous detailing is in order.

[edited for typo]