Any experiance with heat recovery wall fans ?

We are in the middle of building a utility room off the back of the house.

I want to have a pulley hung clothes airer in the roof space and for that I want to have proper ventilation ….currently we have the clothes in the spare room with a dehumidifier and I want to get away from.the dehumidifier

But I’m reluctant to just fire a hole in the wall and put an inline fan as due to the site aspect I’ll get more air coming in the way when the fans off than other wise due to the previous experiance with the kitchen fan that used to face the same way.

Would a heat recovery fan help this situation – looking to remove warm.damp.air and replace it with warmed up external air.

Any recommendations for a unit. I’ve seen many and many variances in price……from 200 quid to 2000.

Specifically I’ve seen the vent axia terpsta lo carbon.

Am I barking up the right tree ? I think whole house pressured systems are over kill although probably more efficient the house hasn’t got any damp issues otherwise just damp washing :)

Not any experience of heat recovery fans but if your project involves a building inspector visit they will expect to see an extractor in a utility room, irrespective of whether you use it. Just a heads up so you don’t fail building control.
The inspector was surprised and almost impressed that the builder remembered to do this after our house rearrange. Didn’t have the heart to tell him that this was actually lazy builder as the room was previously a bathroom and so bricking up the hole would have been harder.
We have the fan on a separate switch from the light as it isn’t often used.

Aye they can expect away.

No building inspector required. It was a shed previously the building works all been signed off.

But I understand ventilation is required…..regs or not it’s only logical for the purpose of the room.

It’s how i achieve that that’s questioned here.

Heat recovery is dependant on good impermeability to work right, I’d imagine your house would most likely fail that condition if it’s anything like mine (mid 60’s build).

Why not use a cowl with an in build flap and an extra damper if needed? We have a cowl like that on our kitchen extractor and it keeps most of the draught out (neoprene lined so it doesn’t bang in gusts either). Cheaper to start there and work something else out later if need be than spend money on something that wouldn’t work.

Of course you could seal up the drying room from the rest of the house and draught proof it before sorting heat recovery, that’s another option.

Heat recovery is dependant on good impermeability to work right

Say what? WTF does that mean in English? Heat recovery is the flow of heat from a hot ‘body’ to colder one (2nd law of thermodynamics iirc). Transfer from the warmer extract air to heat up the colder incoming external/outside air. Probably through a crossflow heat exchanger… (pretty sure it wont be a thermal wheel in this case… 🤪)

Water vapour is held in suspension until 100% humidity level (and the amount is dependent on temperature). At saturation there’s nowhere else for the vapour to go and you’ll get condensation on the coldest surfaces. Ventilation is needed to replace the saturated air, recovering the heat being thrown away is more energy efficient.

Unfortunately I don’t know then efficacy of the Vent Axia (or other domestic) unit. But making sure that any short circuiting of the extract and inlet airstreams would be beneficial (ie, location will be important).

Of course you could seal up the drying room from the rest of the house and draught proof it before sorting heat recovery, that’s another option.

Drying room is sealed. That’s part of the issue.

It’s fully 2 part epoxy foam on the inside and on roof and 100mm kingspan on floor and outside walls under cedar cladding. With all voids foamed and taped …. The roommits attached to is built fully to modern regs with breathable.membranes and 170mm of insulation through out.

There’s currently zero ventilation of draughts due to design short of opening the trickle vent on the window.

It has heating but the last thing I want is a moisture laden room where nothing will dry.

Simply putting a plain old fan on doesn’t solve the issue it just makes for a noisy way of moving warm wet air to the outside.

Can I ask why you don’t want to run the dehumidifier? I’ve got one that has a humidity setting so you could just leave it switched on at the setting u want and it will just switch on and off automatically. You could even use the option for it to drain through a hose if you can’t be arsed emptying it.

Because the dehumidifiers noisy & takes up floor space + needs space round it to work effectively.

Also supposed to be in the van during winter storage rather than my utility room drying laundry

As above – can you not run the dehumidifier in the closed / sealed utility? The mildly warm, dry exhaust air can also be your heat source.

Dehumidifier is running fan plus condenser (which also emits heat). Your proposed option is running fan plus some other heat source (unless you have solar gain) so payback on an expensive fan will be a loooong time (as you already own the dehumidifier).

My experience of bigger heat transfer units is that they need a decent airflow and properly thought out condensate drain or they end up a black gunky mess inside.

Edit – posted after your reply tr

These definitely make sense as they heat the incoming air with the air extracted, which will also lower it’s relative humidity so good for drying and overall should be more efficient than a conventional fan that will just suck air in gently through other gaps in the house.
I’m also curious about them but when looking couldn’t find anything about stated efficiency and also wasn’t sure whether the inevitably slightly colder air coming in would make that one room colder rather than trickling in everywhere and being heated in multiple locations.
Would also like to know if anyone has experience of one as they are not cheap bits of kit.

86% efficient was one number I saw being bandied about for the ventaxis unit.

You’ll.never achieve 100% but when it’s 18 inside and -5 outside in winter…..it’s gonna make an odds

86% efficient was one number I saw being bandied about for the ventaxis unit.

I’ve seen those and wondered about putting one in the workshop.

My main concerns are:

1) how does it behave when switched off and the wind blows against it – I assume you just get cold air coming straight through – unless it closes off the aperture…

2) How efficient is it when the temp difference isn’t that high eg we don’t heat the workshop much in winter, so it’s 10 C inside and say 5C outside, wonder if it gives you much benefit in that situation.

Say what? WTF does that mean in English? Heat recovery is the flow of heat from a hot ‘body’ to colder one (2nd law of thermodynamics iirc). Transfer from the warmer extract air to heat up the colder incoming external/outside air. Probably through a crossflow heat exchanger… (pretty sure it wont be a thermal wheel in this case… 🤪)

Wrong word, I meant infiltration. As in, the addition of unwanted air. I know fine what heat recovery is but the exchangers don’t work properly unless you can control where the air gets in (ie. the exchanger and not a million gaps in the floor, walls etc.). Sorry, I’m tired as my ****bag neighbour decided half one was a good time to crank out some choonz.

MVHR systems are available for domestic applications (see Figure SG2.20) but it is essential that they are installed in buildings that are really airtight to start with. Otherwise any attempt to pump air around the system may just increase the flow of air through unwanted air infiltration paths. However, once the fabric heat losses of a building have been tackled with thick insulation and high-performance windows, this may be the only satisfactory way to deal with the remaining major heat loss, that from ventilation.

Drying room is sealed. That’s part of the issue.

It’s fully 2 part epoxy foam on the inside and on roof and 100mm kingspan on floor and outside walls under cedar cladding. With all voids foamed and taped …. The roommits attached to is built fully to modern regs with breathable.membranes and 170mm of insulation through out.

There’s currently zero ventilation of draughts due to design short of opening the trickle vent on the window.

Sounds ideal then, I’ll see if I have anything useful to ping you later on.

I installed a VentAxia Tempra thing in the utility room of our last house, because we used to dry washing in it but it wasn’t very big and did feel quite damp sometimes. We used to open the window when we hung new washing up or the window and window in the door would be soaking by the next morning, and it made the rest of the house a bit wetter too.

We didn’t open the window at all after it was in, and the windows still got a little condensation at the bottom but nothing like what it was. It was a little cooler than with the window shut, but warmer than with it open.

The largest downside was that it was quite noisy. It went into a high speed mode if you pulled a cord; this was very noisy indeed. Even on low mode I’m glad it was in a utility room away from quiet areas of the house. One in a bathroom near bedrooms for example would be a bit too noisy for me.

86% is pretty efficient.
Provided there the flow is low so the total air volume isn’t changed too often the room should stay fairly warm. Not sure what the economic payback is but means you get fresh air circulating with less heat loss rather than the stale but dry air that a dehumidifier would give.

Philll how noisy we talking. I mean the washing machine in the utility and immin the room next door with the door closed.

I’m aware the washing machine is on a spin cycle but it’s very much in the undertones of the noise.

On low we are unlikely to hear it.

Say compared to a bathroom fan -louder or quieter ?

Any of the tradies got any experiance of any quieter units ? I saw a post suggesting the terpsta was too small a unit for a room my size and going up to the next unit up which looks like the size of 2 breeze blocks and is an extra hundred quid would be far more benifiicial than running the small unit on turbo more often.