To loft or not to loft?

[Barnacles]

Hi all,

I installed a system based around a Brookvent unit in a new build that I did around 3 years ago and I was never entirely happy with the system. It worked well enough but I see now how I could have improved upon the system. With that little bit of knowledge and experience (and the copious amount of knowledge that I have gained reading posts on this site) I am now set to install a new MVHR system in our current property.

 

We now live in a modest 1850s stone built, 3 bed detached house which gets little direct sunlight in the colder months. It has a 1970s extension with cavity walls (rendered concrete and thermalite block construction) which accounts for about a third of the building. Damp is a big problem and I am working through various solutions to try to help minimise the moisture entering the house such as ensuring that all guttering is performing well, surface water runs away from the house, paving levels are low enough etc. etc.

 

Clearly I have my work cut out to make this a comfortable, healthy home for my family. There is a lot of moisture and a bit of mould is starting to develop as we come into the colder months and the windows are open less. So, part of my grand plan is the MVHR system. I have purchased the kit (based around a Titon unit) and having agonised over the design for months I am almost ready to get started. I had originally planned to locate the unit in the cold loft but it seems that current advice is to locate it, and the manifolds, in a heated part of the house. I started to look at the airing cupboard as an alternative but my wife was not entirely pleased with that solution as we have precious little storage space in the house anyway.

 

My proposed solution (and what I would be interested to hear people’s opinions on) is to locate the unit and manifolds in the loft and construct an insulated housing around it. I also plan to put a small, thermostatically controlled heater (perhaps 25w or so) to keep the temperature up around 18-20 dec C.

 

My questions are; is this a logical, sensible solution? Do the MVHR units need to “breathe” - does it need to be in an open environment to prevent over heating the unit? Would a heater be required or would the heat generated by the fan motors be enough to heat that small space?

 

Any advice is greatly appreciated.

 

[scottishjohn]

maybe look at stopping the damp in the walls  to start with 

sort the problem at its base -- not try to get rid of damp once its got in 

 MVHR will not be your solution I feel 

"drain the swamp  once--don,t fight the alligators for ever"

[MJNewton]

If you do opt to insulate the unit (I think they tend to be fairly well insulated already though?) then rather than have to build an enclosure I imagine an easy way to do it would be to silicone panels of PIR board on to the main faces on the unit? You'd need cutouts for the condensate drain and filter access, and I don't think you'd need the top covering as it's mainly pipework anyway (which should themselves be insulated). 

[AdamSee]

I have a similar issue to yours. My plan was to partial convert the loft to a insulated "room/hutch" for the MVHR using stud walls and filling them with insulation. I could lift the insulation below it so its heated with the rest of the house......not sure if this could lead to over heating in the summer tho. The new "room" would only be about 1.5m x 1.5m. But should be enough to squeeze everything in. 

 

[oranjeboom]

Can't comment on the damp issues.

 

I have mine in the loft and have it sitting on a timber platform on the ceiling joists (with circa 200mm loft roll). The timber platform has a foam type mat to reduce any vibration to room below. Plan was then to insulate the whole unit further with 150mm PIR and any left over loft roll. It can get to 50C up there in summer, so hoping to protect the unit from that.

 

Just bear in mind that any insulation you add has to be removable to get to the filters and maybe the control panel.

[Jeremy Harris]

An MVHR in a "cold" loft space normally has to be insulated, as do all the ducts in that space.  It also means that the ducts needs to be well sealed to the VCL where they come down into the heated envelope.  Given that good access is needed every few months for routine maintenance, filter changes, cleaning out all the dust and flies etc on the intake side, plus occasional cleaning of the heat exchanger, I'm not sure that loft installation is ideal.   You also need to ensure that the condensate drain cannot freeze, so that needs to be insulated as well.

 

I mounted our MVHR unit inside the heated envelope, at the rear of our services area.  I can access this via a door from the spare bedroom, but space is tight in there and it's far from ideal in terms of cleaning and changing the filters.  I'd not particularly want to have to crawl around in a loft doing this every few months.

[Barnacles]

Thanks for all the great information.

 

What I had in mind is very similar to what @AdamSee suggested. Probably knock up a CLS frame, screw/glue PIR on to all faces and keep one face easily removable for maintenance. I want to mount the manifolds in there too as the ones I have are uninsulated so I am guessing it will be around 1.2 x 1.2 x 0.9 or so.

 

The unit will be mounted very close to the loft hatch so to clean filters etc I shouldn’t even need to get into the loft, I can do it from the ladder. I also plan to extend the wires to the control panel so that I can locate it somewhere more convenient in the house eliminating the need to access the unit to tweak the settings.

 

@scottishjohn , the MVHR is indeed just a part of the solution, I have much work to do elsewhere in the building. It’ll be a long process but I am hoping that for a relatively small outlay the ventilation system will start to help and make the house more liveable. We’re also running the heating more than we normally would to help with drying the walls etc. and looking at problem areas to see how we can address the problems. I suspect a big part of the problem may be the painted cement render which covers most of the building and probably locks in a lot of the moisture in the walls, that’s a job for next year.

 

One aspect I haven’t yet looked into is insulating the ducting - thanks for the reminder @JSHarris. It seems that the various types of insulation I have looked at appear to have only one thing in common, they are all very expensive! Is there a consensus on which type is best in terms of price/performance? I am using 75mm semi-rigid ducting.

[joe90]

34 minutes ago, Barnacles said:

One aspect I haven’t yet looked into is insulating the ducting

 

Is the loft insulated ?, run the ducts under the loft insulation. Our unit is in a warm loft but I still had to insulate the in and out ducts to the outside as condensation was forming on the “in” duct.

Edited October 14, 2019 by joe90

[Ed Davies]

2 hours ago, joe90 said:

run the ducts under the loft insulation.

 

Only the supply (to the house) and extract (from the house); not the inlet (from the outside) or exhaust (to the outside) which should be at near-to-outdoor temperatures, of course.

[Barnacles]

15 hours ago, joe90 said:

 

Is the loft insulated ?, run the ducts under the loft insulation. Our unit is in a warm loft but I still had to insulate the in and out ducts to the outside as condensation was forming on the “in” duct.

 

The loft is insulated with lovely fibreglass. The problem is that all the trusses run perpendicular to the runs of ducting. I had considered adding more insulation over the top of the existing which would allow me to run ducting in an insulation sandwich I suppose.

 

Also, I can’t remember where I read it but I got the impression that it was no longer an acceptable practice to insulate the ducting this way?? Anyone else seen/heard that?

[Hastings]

On 15/10/2019 at 09:04, Barnacles said:

no longer an acceptable practice to insulate the ducting this way?

Did you find out about this? I hadn't come across it and am about to start my MVHR installation.

 

Had been worrying a bit whether burying the ducting under the loft insulation was going to be very effective, especially as it has to cross over some of the roof trusses. Was planning to lay 100mm insulation first, then the ducts, then 200mm more and hope the ducting doesn't prevent the insulation from fitting together snugly.

Edited October 9, 2021 by Hastings