Heat Recovery System

[Danm54]

Has anyone installed a small heat recovery system in their house and is it worth it?

We currently have a shower room downstairs with no fan and we had very little heating during last winter, so the shower room is the only place we've seen condensation.

I've created a new main bathroom upstairs and the upstairs toilet will become an ensuite with shower so I was thinking of using a heat recovey unit instead of 2 extractor fans?
Take the heat from those rooms and duct it downstairs probably. We live in a Welsh cottage and I've gone mad with insulation in the dormer roof so upstairs rooms are warm, but downstairs can still be chilly with the stone walls.

I'd only want the unit running as an extractor fan would, so comes on with the lights or humidity.

Is it possible and worth doing or a waste of time and I should stick with normal extractor fans?

 

[HungryHippos]

No I had a heat recovery system on my old house, was noisy and annoying.

Get extractor fans instead.

 

[Danm54]

No I had a heat recovery system on my old house, was noisy and annoying.

Get extractor fans instead.

Thanks for the input. I hadn't considered noise really, assumed they'd be nearly silent or no louder than an extractor fan would be.

 

[HungryHippos]

Thanks for the input. I hadn't considered noise really, assumed they'd be nearly silent or no louder than an extractor fan would be.

I had an MVHR system that had a big unit in the loft, with ducts running all over the place.

Impossible to individually turn any of the vents off, and they were always operational. The unit in the loft was dumb with no way to control it without going into the loft.

Think you'd be better off with extractor fans, and maybe add some kind of split air con to help with temps.

 

[sovietspybob]

I looked into these when building our house, i think unless you've got a whole house system and you have something like a log burner in 1 room which you can extract lots of heat from they're not really worth while. Also as HungryHippos says a lot of systems seem to be pretty dumb, not many options seemingly to put the heat where you actually want easily.

 

[Kamakazie!]

They won't be able to specifically heat a room if you have inlet's in multiple rooms, but if you are wanting to extract to 1 and inlet to 1 then all heat will be pumped to the same room.
Single room extract / inlet will be pretty cheap (though obviously significantly more than a simple extract fan), and shouldn't be at all noisy if appropriately sized & ducted.

That said, in old houses, the benefits to heat reclamation can be pretty small as you have so many other losses of heat due to draughts etc.
Other consideration for these is the air quality improvement you can get, which is often a selling point.

 

[Danm54]

Hmm, few different opinions then.

I won't be going for a full house system, I did think about it briefly but the ducting won't be easy to route through this house and the cost would far outweigh the benefit.

So I guess it's a unit for each bathroom, extracting and venting back into the same room, or go with 2 extractor fans.

I'll have to look into the cost of 2 small units but I'm guessing it'd be significantly more than 2 inline extractor fans at ~£90 each.

 

[Kamakazie!]

You wouldn't usually inlet into the same room that you extracted and typically wet areas have extract and dry inlet.

You'd probably just be better off with the 2 extract fans. If you wanted, you can get single room MVHR (for the downstairs only) from vent-axia and a few others that are basically a just an extractor that does some heat reclamation in line. This would mean you are not losing even more heat from downstairs.

 

[Doobedoo]

You really need passivhaus levels of insulation and air tightness for it to be worthwhile, most housing including modern build will not be suitable for it. Spend the money elsewhere.

The heat losses of the building are reduced so much that it hardly needs any heating at all. Passive heat sources like the sun, human occupants, household appliances and the heat from the extract air cover a large part of the heating demand. The remaining heat can be provided by the supply air if the maximum heating load is less than 10W per square metre of living space. If such supply-air heating suffices as the only heat source, we call the building a Passive House.

https://www.passivhaustrust.org.uk/what_is_passivhaus.php

 

[Danm54]

Thanks for the advice, think I'll stick with a couple of extractor fans.

My thought was to try and reclaim some heat from the steam from showering but it doesn't look like it's viable really.

I'm putting in quite a bit of effort to insulate upstairs, including a 25mm celotex thermal barrier wherever possible and fully taping joints etc for a good vapour barrier, but it's not going to be passivhaus standards. Plus downstairs has stone walls about 50cm thick so they're never going to be air tight.

 

[FreeStream]

Fitted one to my Top-Floor flat. I already had secondary glazing over my sash windows, dealt with as many draft points as possible, etc.

The extract humidity speed control was dumb so I wired up a RPI and a few sensors to do intelligent control of it, now only really ramps up during showers.

Result is no more mould or condensation on windows (before even the secondary glazing would have condensation on it on colder days). Relative Humidity is kept at 50% when possible, clothes dry quicker, etc...

Well worth it just for the reduction in humidity. Plus given we no longer need to run a dehumidifier, or have the windows open, and capturing 90%+ of the heat from showers means that the £10/year running costs are probably covered and more.

Gas use dropped about 10% after fitting it, but not really statistically relevant given the internal/external conditions were never equal!

Friend of mine also fitted one in his house, same benefits, no more mould build up in the winter, less condensation on windows (no secondary glazing in his case), etc...

 

[eviled]

@Danm54 I assumed you meant a single room solution, something like https://www.vent-axia.com/range/lo-carbon-tempraselv

I always wondered if these would make a noticeable difference.

@FreeStream what unit do you fit?

 

[FreeStream]

https://www.vent-axia.com/range/sentinel-kinetic-bh

Something like that.

Extract in kitchens and bathrooms.
Supply in bedrooms and living rooms.
Exhaust using an existing vent outlet
Intake is on the roof using a raised intake to avoid getting the heat from the roof in the summer!

Has a summer mode to dump excess heat which is semi-useful.

 

[HungryHippos]

https://www.vent-axia.com/range/sentinel-kinetic-bh

Something like that.

Extract in kitchens and bathrooms.
Supply in bedrooms and living rooms.
Exhaust using an existing vent outlet
Intake is on the roof using a raised intake to avoid getting the heat from the roof in the summer!

Has a summer mode to dump excess heat which is semi-useful.

I had one just like that in my old house, was noisy, and I didn't really notice it doing much, not to the humidity nor the heating bills.

In summertime, indoor temps would reach about 30c and even whacking the boost mode on did about zero to keeping summer temps down.

Nice idea in theory but I'd prefer standard trickle extractors which are capable of keeping humidity down, that's what I have now (they never turn fully off).

If they could actually run silently then I'd be more interested in such a system in the future, but my supply vents in the rooms were all various degrees of noisy.

 

[FreeStream]

Yep the standard control of the unit was terrible and noisy.

Now it’s properly controlled it varies the fan speeds from 5-100% based on the delta to a target humidity and varies during the night to further reduce noise.

All bedrooms have silencers which made a big difference too and now barely audible in rooms with them even at 100%.

I have years of data and 100% makes a difference, time for bathrooms to return to nominal relative humidity, etc.

Won’t have a house without one now!

Obviously it’s more effective the less leaky the house is! Plus an MVHR is not designed as a heat extraction device, so you can’t expect it to do so.

 

[Danm54]

@eviled I've seen those in my searches but I'm after a loft mounted unit, keeps the fan noise out the room and those units aren't exaclty pretty.
Right idea though, recover some heat lost while extracting hot air.

@FreeStream I only really want to extract from a bathroom and ensuite, and it's not something I'd want running continuously so light activated would be ideal.
As above it needs to be loft mounted and I don't have that much room to play with. Also the unit you linked to is on the pricey side.

I do like the humidity control though, that would be nice to have.
It may be something that I leave space and wiring for and revisit later once the house refurb has stopped draining my bank account.

 

[HungryHippos]

Yep the standard control of the unit was terrible and noisy.

Now it’s properly controlled it varies the fan speeds from 5-100% based on the delta to a target humidity and varies during the night to further reduce noise.

All bedrooms have silencers which made a big difference too and now barely audible in rooms with them even at 100%.

I have years of data and 100% makes a difference, time for bathrooms to return to nominal relative humidity, etc.

Won’t have a house without one now!

Obviously it’s more effective the less leaky the house is! Plus an MVHR is not designed as a heat extraction device, so you can’t expect it to do so.

Yeah my house was pretty well sealed, no trickle vents, new build, triple glazed etc.

Still, the supply vents in the rooms were pretty noisy and, like you said, dumb. Would be OK if it was smart enough to turn off overnight for example, or to give me that control option.

The controls were all on the unit in the loft though, had to be in front of it to do anything, crazy.

Maybe better if it's done right and with smarter controls in place.

 

[Danm54]

I've done a little searching and the idea came to me that I only really need the heat recovery core. I can then use standard fans with humidity and timer controls, activated by the light.

I've only found one core so far on ebay, called a passive heat recovery unit, but I'll look at some brand names to see if they offer the same.

Edit, controlling the intake fan might be trickier but I'm sure it's possible.