Good afternoon

I’m looking for a half way decent humidistat 6” extractor fan, the room it’ll be in suffers from damp ( one wall is half height below ground level, and house has had all sorts of changes in its history that have’nt helped), the fan is intended to hopefully improve the internal conditions a bit until such time as the causes can be dealt with.
Also internal condensation can be a problem. Lots of fans available, however does anyone have experience of either one they’ve been happy with or ones to avoid. Noise levels will be important.

Many thanks

Thank you

I would go Vent Avia SVARA but only 100mm diameter. But it thinks for you

Posted By: WillInAberdeennasty feeling that my phone is going to stop working with the vent axia app

Why, how?

They behave with Hegemony without Responsibility, aka Enshitification https://en.wikipedia.org/wiki/Enshittification#Reception_and_impact. I hope the Reckoning comes soon, as promoted by https://www.eff.org (Doctorow prominent), like users leaving Twitter for Mastodon, despite the tech monopolies' efforts to lock users in.

I’m a big fan of mechanical heat recovery ventilation systems and you could try it one from Boulder. All the big fan companies make small versions of these now. they’re very easy to install the bungalow because you’ve got the whole roof space to do it in.

I’d be dead scared of any extract ventilation because you could pull fumes from the wood burner in. I know you say it’s ventilated from outside, but I still worry about that.

Don't install a single-unit mechanical heat recovery ventilation system in a bathroom! Or rather, don't deliver the incoming air direct into the bathroom. By all means, extract from the bathroom and recover its heat (incl the considerable latent heat of evaporation of warm water), but let that air be replenished by thoroughly mixed air being drawn in under the bathroom door etc. In other words, a full MVHR system.
I specified a single-unit mechanical heat recovery fan once in a bathroom - disaster! It had to be taken out. The trouble is, the incoming air, though warmed, is by definition still not as warm as the outgoing air so the effect is a definite flow of cooler air in the bathroom - which a naked wet body feels acutely.
This matters less/not at all if the incoming air comes into other habitable rooms, where it quickly mixes its temperature with the house air, before being drawn indirectly into the bathroom

Posted By: HuwblutThanks for your comments everyone. The fire is at the opposite end of the house to the extractor so I'd think it unlikely that it'll pull fumes in. I'll take a look at the new model mentioned above and likely go with one in the kitchen and one in the bathroom with undercuts on the doors.

Sorry, which fire? You haven't mentioned one before? And you seem to have ignored fostertom's very wise advice. Is there a reason for that? Or have I misunderstood?

I seem to remember seeing a simple single-unit heat-recovery fan that had a facility to duct the incoming air. That could enable the incoming to be delivered into the next room, where it would mix into the house's existing air, which would be drawn in at approx bathroom air temp, under the door or whatever.

Hi everyone. Apologies for the confusion. it's a detached bungalow which has been knocked through at the rear to make a kitchen diner (see drawing - the two rooms labeled kitchen are now one room) The wood burner is at one end of the room - it's fed from outside - the flue finishes 4m above the fire.
The fan is planned at the opposite end of the room around 6.5m away in the kitchen area it's purpose is to remove background moisture from the room by way of gentle continuous extract. There'll be a kitchen extractor too. I've planned the fan however if it's felt that it'd pose a risk I'd happily not install it. The bathroom however needs something which could extract shower moisture and smells and gently move the air from the adjacent bedrooms via a minimum 10mm undercut on the doors by either leaving the windows on the latch overnight or installing trickle vents. When I'm there on my own I'll open the bathroom window however my girlfriend has a different opinion on this! I paid for a retrofit report before the project started and the chap suggested MVHR but it was way out of budget. I've attached the floor plan from a pressure test which ultimately didn't work due to lightening taking out the power overnight! The wood burner is near to the 3350 measurement and the fan has been wired but not drilled to the left of the window on the wall near to the top of the ceiling.

I don't really understand the wood burner. Most times when people say "fed from outside" they're referring to a sealed stove type burner. It seems like you're talking about an open fire that has an external air feed that pops up somewhere near the grate. Is that correct?

If so I don't think the air feed will work the same way as one works with a sealed unit that has the chimney draw helping the draft. Do you have a model number?

When you say 3350 measurement did you mean to say 3750?

For the bathroom, I'd be tempted by a ducted single-room MVHR as Tom suggested, extracting from the bathroom and feeding fresh air into the adjacent bedroom.

OK, it says it's a stove and looks like one, so now I'm confused about why "the flue finishes 4m above the fire"? Why doesn't the flue connect to the flue outlet on the top of the stove?

I'm not familiar with single room MVHR units so I'll leave it to others to suggest one that is ducted to supply another room.

Some work like that, others are just small versions of a standard MHRV with two fans for continuous supply and extract and a heat exchanger.

Eg ducted single room (actually two-room)
https://www.fastlec.co.uk/vent-axia-hr100r-heat-recovery-unit-top-access


The push-pull type are recommended to use in pairs eg one in the bathroom and another in the kitchen. They synchronise so that one is on intake while the other is on extract, that way no pressure difference builds up.

The push pull type seem to be gaining market because they are often quieter, use less power and have higher % heat recovery. Still quite pricey though.

Obviously a continuous extractor fan would create more negative pressure than a push-pull, but for a retrofit airtightness isn't going to be a problem.

Just thought I would add some feedback from using a push pull type, single room MVHR. Its in a bathroom in a part insulated farmhouse on Dartmoor and we were worried about potential damp problems so wanted a bit more than a basic 4" extractor which we have not been greatly impressed with in the past.

We went with a BSK Zepher and its been in a year. It's been perfect at managing humidity as it also has a humidistat built in so its extracting when humidity is high and it defaults back to the push pull mode when the humidity comes back down again. It clearly returns some heat as I've looked at it when it's running with an IR camera but doubt its claimed efficiency. Not noticed any problems Tom mentioned with it creating chilly air but we do have a full shower enclosure so you are in your own hot bubble when showering.

Worst aspect is when there are smells in the bathroom. It doesn't switch on from the light circuit so doesn't automatically extract when someones in there. If in push pull mode it pushes smells out into the corridor beyond it. This would be horrible if paired with a second unit in a kitchen as mentioned above. It can be manually set to extract for 30min when your in there which is fine for residents used to it but guests dont know to pick up the mini remote and set it to extract.

Posted By: fostertomWhat about when you get out of the shower all wet - or do you dry yourself inside the enclosure?

Hi Tom.

By the time we get out the humidistat has kicked in and its just extracting so no cold from outside being drawn in just warm air from the rest of the house. In dry times (rare on Dartmoor) it might not quite have kicked in by the time you get out but not noticed a cool draft. The room normally rises in temp by a degree or two from the warmth from the shower. We normally run the MVHR on it's lowest anyway setting as this seems to keep the room nice with no noticeable drafts to me but we are probably not as fussy as some haha. The only time we run it at higher settings is when drying cloths in there.