Single room MVHR advice please

phil24_7

I am looking at installing a single room MVHR unit in a cellar room that has no ventilation.

Does anyone have any experience and recommendations about what unit to use?

The room is 8.5m long, 3.3m wide and has a large door and window (no trickle vent) at one end of the 8.5m. It also has a fire door half way along that leads into the original, stone walled cellar. This room is fully carpeted and plastered (including tanking) so doesn't suffer with damp walls, just no air movement and any air circulation coming from the musty cellar area.

I was thinking of installing it furthest away from the door and having a dehumidifier at the other end.

Any problems with this?

Regards
Phil

malc_b

If it doesn't suffer from damp why the dehumidifier? As long as the inside temperature is higher than outside then the air coming in should become lower in humidity. The MHRV unit recovers the heat so the incoming air will be dry air as it has warmed it. BTW the MHRV unit will need a condensation trap so you will need something to pump that unless you plan to install the MHRV unit above drain level. A waterless trap is best (or straight to an outside gulley maybe).

phil24_7

It doesn't suffer damp walls but...I currently have a problem with door seals letting some water in as well as damp on the outer skin of the external wall due to an issue that will be sorted soon. One or the other of these is causing a wet carpet by the door. That and the fact that the only air it gets is from the musty cellar means if does suffer with high humidity at the moment. Once the door seals, external drainage and ventilation are sorted it will be there as a 'just in case', due to what I will be storing in there.

I will be able to drain straight through the wall as there is a rain water gulley running alongside the cellar that slopes to the rear of the property.

Regards
Phil

malc_b

Right, so your question was more can I have a MHRV and a dehumidifier. Answer is yes, assuming the dehumidifier is not extracting the air to outside, if such exist even. A standalone unit won't interfere with the MHRV unit. The MHRV performance will be more affected by draughts through windows and doors as for best function the house or room should be sealed so all air coming in or going out goes through the MHRV unit.

You might have a look at venta axia perhaps. I've found BPC Ventilation to be very helpful (DIY in my case but they also do an install service) so I'd suggest asking them for advice.

phil24_7

malc_b wrote: »

Right, so your question was more can I have a MHRV and a dehumidifier. Answer is yes, assuming the dehumidifier is not extracting the air to outside, if such exist even. A standalone unit won't interfere with the MHRV unit. The MHRV performance will be more affected by draughts through windows and doors as for best function the house or room should be sealed so all air coming in or going out goes through the MHRV unit.

You might have a look at venta axia perhaps. I've found BPC Ventilation to be very helpful (DIY in my case but they also do an install service) so I'd suggest asking them for advice.

I know I can have both as they do different jobs but was simply curious as to whether my placement would be okay or if it would be better having both at the same end. My real question was which single room MVHR do people recommend or have experience with.

The room is sealed quite well as it has a double glazed window and door (though this leaks a little) at one end and a heavy firedoor with smoke strips half way along one wall. This door only has 2 or 3mm clearance underneath so no draughts to speak of and limited chance for air to get in.

Maybe a balanced flow MVHR would be best due to it being quite well sealed and the only room air can leak into is a musty, unheated cellar?

phil24_7

Thank you for the pointer to BPC, I will drop them an email once I have exhausted the lovely forum peeps knowledge/advice.

Regards
Phil

malc_b

MHRV are all balanced flows. Otherwise they are just ventilation units. HR is heat recovery so you have to take the heat out of the outgoing air and give it to the incoming for it to be HR. So in you case you have inlet and outlet and put these roughly in opposite corners. In a whole house MHRV you put the inlet or outlet as far from the door as possible usually (the air going in/out the room comes via the door). Unless there is another factor of course, so in bathrooms the outlet goes near the shower.

phil24_7

I thought single room MVHR units had either a negative pressure or a balanced pressure (spec/model dependent)? I would be looking at a through wall, all-in-one MVHR, no inlets/extra outlets etc.

malc_b

MHRV = Mechanical Heat Recovery Ventilation. If you are not extracting air how can you recover heat? And if you are not injecting air how to you use the heat you have recovered? All MHRV units must both extract and inject. Just extracting is call an extractor. Just injecting is called a PIV, Positive Ventilation. Both of these don't recover any heat, they just help with damp. And with these you will also need some trickle vent in the room to allow air in, for the extractor or air out for the PIV.

ComicGeek

You can get decentralised MVHR units called dMVHR which will do supply and extract in a single room with heat recovery - no ducting, just a through the wall system. All the major manufacturers do them; Vent-Axia, Nuaire, Xpelair etc.

Intake and extraction is at the same point, so I wouldn't expect it to work well on deep rooms as no real throw on the supply air - designed primarily for bathrooms and utility rooms. 8.5m is fairly deep, so your idea of having this at one end and the dehumidifier at the other seems sensible to me.

Google Xpelair dMVHR - they have a good domestic ventilation system guide which shows all of the options and how they're installed.

phil24_7

malc_b I know all of this but thanks!

From my brief searching I can see that not ALL MVHR's are balanced.

I can't see how trickle vents are needed in most cases unless your house is air tight. I have effective extraction in my bathroom that just sucks air from the rest of the house, that is in turn sucked in through gaps in the fabric of the building.

But this is all besides the point. I just want pointers as to which through wall, single room MVHR I should get!