Hi,

I live in a 1950s semi, which I am going to be extending (awaiting a decision on planning).
Most of the original, external walls will be subject to the extension and therefore the new external walls will be properly insulated, however, most of the front of the house and one part of the rear upstairs will remain original.
Bizarrely, the house has almost no cavity, so I’m looking at internal or external insulation panels for the relevant areas.

The house is quite humid, which has caused some mould growth, so I’m now ventilating twice a day by opening all windows for about 10 mins and running a dehumidifier when the windows are closed.

Therefore, I’m going to need to fit some kind of automated ventilation.
I considered an MVHR system, but it would require substantial changes inside the property, including boxing in of pipework, so it’s not suitable.
We also know peoples who have recently fitted a PIV system and they said the incoming air is cold, so we want to avoid that.

We seem to be left with adding individual heat recovery ventilation units in rooms (probably not all), but I’d like to get some feedback from people who are using them.

Does anyone here have these things and are they any good?
How much noise do they make?
Recommended brands?

Thanks!

MVHR should be possible upstairs

PIV should be illegal as although it works it also pushes warmed air out of the house increasing energy use!

"PIV should be illegal as although it works it also pushes warmed air out of the house increasing energy use!"

Yeah, but so do trickle vents, notionally.. Prrhaps one day we won't have to put up with such medievality as standard

Ducted fans (central MHRV system) have to overcome a lot more backpressure, due to all the ducts and valves, than single-room MHRV do or push-pull MHRV or PIV. So in principle, ducted MHRV uses more electricity than those.

But in practice, a very wide range of quality is available, with some (very expensive) fans consuming much less electricity than some other (very cheap) ones.

So overall: it depends.

Here was another discussion about how to retrofit Mhrv without fitting ducts everywhere
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17632&Focus=298694#Comment_298694

Quick Google, first hits:

Vent axia PIV : 6.5W at 29l/s "Pozidry"

Vent axia dMEV : 3.5W at 29l/s "Lo carbon NBR" (2 units required)

Vent axia MHRV : 27W at 29l/s "Sentinel Kinetic B/BH vertical spigots"

So their MHRV uses several times more electricity than their PIV or dMEV for the same ventilation rate.


Obviously none of those are a lot of power consumption, in the scheme of things. And there are many other suppliers and models . And many other factors, such as: energy and carbon value of the heat recovered by the MHRV and avoided cost of heaters to supply it; cost and practicality of fitting ducts; ability to control the air flow rate to the rooms that need it at the times when they need it; noise; space taken up, unit cost, reliability, maintenance, filtration, discomfort of cold air supply, etc etc etc


So overall: it depends.

<blockquote><cite>Posted By: Mike1</cite><blockquote><cite>Posted By: alexeix</cite>I considered an MVHR system, but it would require substantial changes inside the property, including boxing in of pipework, so it’s not suitable.</blockquote>I think it would be worth exploring that further, if you provide more details & perhaps a sketch.

Thanks for the feedback - interesting to read your comment about the wind tunnel effect.

Regarding the design, we may be able to fit MVHR with only one section of ducting passing down from the loft area to the ceiling of the ground floor.
However, this throws up another potential issue, because the only available loft space will be in the extension added on to the back of the house.
Does the actual heat exchanger unit need to be centrally located?

Another issue is that there is artex on a number of the ceilings and it’s old, so I suspect it may contain asbestos.
I’ll get it tested to be certain, but if it is, I won’t want to be cutting holes through the ceiling.
Hence why I’m interested in room specific units.

To cover all the bases, I’m going to lift the carpets and check which way the joists run on the first floor, because that will also affect our ability to do a full MVHR retrofit.

Will try to upload a sketch when I can figure out how. 😁

Posted By: alexeixRegarding the design, we may be able to fit MVHR with only one section of ducting passing down from the loft area to the ceiling of the ground floor.

Sounds promising

Posted By: alexeixDoes the actual heat exchanger unit need to be centrally located?

The aim is to keep the external air supply and exhaust ducts as short as possible and very well insulated (both will carry very cold air in winter), with their vents on the same elevation. So the exchanger probably won't be central.

Posted By: alexeixthere is artex on a number of the ceilings and it’s old, so I suspect it may contain asbestos.

If it does, you can buy Artex removal gels, allowing you to remove the Artex where you need to cut without creating dust.

Posted By: alexeixWill try to upload a sketch when I can figure out how. 😁

Keeping the tiny is the key - from memory I think the limit is 50 kB?

Posted By: alexeix
Does the actual heat exchanger unit need to be centrally located

No it doesn’t. You only aim for that to reduce the length of the multiple pipe runs and therefore the cost. Rooms that are furthest away could have 2 x pipes going to the extract and/or supply plenum (if using flexible semi-rigid duct)