Single room heat recovery in bathroom

@pottyone72 how have you got on with your Kair K-HRV150? We finally managed to get an electrician round to look at quoting on fitting one and he basically thought I was mad for not putting in a normal extract fan…losing confidence in my choice now…he will put it in but has pointed out we’ll have a larger than normal hole if it doesn’t work out, and doesn’t see the point.
@Phoebe_Spence @Alan_Mould how noisy are they and what if its humid outside, do you just turn down the humidistat? Do you run it all summer (we would usually just have all the windows open then as relatively secure and quiet here)? thanks

Hello Lisa, i would just say background fan hum, not noisy. There is an option to turn off during the night, when dark.
I just set the humidistat to 65% so it only comes on when necessary. So you could open windows as you wish, it doesn’t turn on unless humid, so you don’t need to be adjusting settings.
I would definitely say heat recovery is worth it. I didn’t notice that the hole in the wall was that large.
But my experience is that the fitter hadn’t read the instructions properly so had to get them back as the side inlets were blocked and the external vent/outer cowl wasn’t correctly fitted. Electricians need to become more familiar with developments. Not easy to find builders/electricians who are interested …
You’d be welcome to visit to see one in action - I live in Stockport

Ignore the electrician unless he happens to be a qualified retrofit coordinator. My plumber hates pipe insulation but I only employ him for his plumbing skills.

If the windows are open in summer you can safely turn the unit off.

1 Like

My plumber hates pipe insulation too!! :grimacing::joy:

Hi Lisa
We’ve not had it fitted yet. Only because we’re staging the work in the bathroom and can’t put the fan in until our bath is removed.
Currently we are using our Ebac dehumidifier in the bathroom to dry clothes - once the ventilation unit is in, we won’t need to use the portable dehumidifier in the bathroom .

Hi Lisa,

I agree entirely with Phoebe here. The fan on “standard” mode makes little noise - it is less than the hum you get when a fridge is on for example. We have 2 including one in our ensuite and we always sleep with the door to the bedroom open. The noise never disturbs our sleep and the fan provides some air flow. The fan only goes into boost (which is about the same noise as a normal extractor fan) when the humistat says it needs to - ie when you have had a shower or put up clothes to dry or whatever. As soon as it is below whatever level you set it at it turns back down to “standard” mode.

Sorry but I don’t understand your comment about it being humid outside - the mode changes depending on the humidity in the room, it is nothing to do with the humidity outside.

Like Tim, I would not worry about what the electrician said. Our constant and unaltering experience of a year long retrofit is all contractors want to do what they are used to doing and hate doing anything else, no matter how sensible it is. So plumbers hate pipe insulation; electricians hate any devices they are not used to wiring, builders hate putting in more insulation that they are used to putting it, and hate any taping you want; builders won’t stop dropping mortar in the cavities, etc etc etc. We found it is a constant battle against the contractors you employ. Of course employing specialists in retrofit should get round these problems, but certainly when we need it (6 years ago) they were as rare as hen’s teeth.

All I can say is that the Kair fans we have are excellent and one of the best things we did. Like Phoebe you are welcome to come and see ours if you want, we live in Fallowfield.

And still are. That’s why I bought into People Powered Retrofit.

@Tim_Gilbert @pottyone72 @Phoebe_Spence @Alan_Mould thanks all for your replies, I was just having a wobble!! Thanks for the offers to look as well, as we are in Cumbria we’ll not take you up on it, but you’ve given me the confidence to go for it!


I have wobbles about my choices all the time too :grin:
This group and the people in it provide me with the facts, the science and peace of mind to have more confidence in my choices.

1 Like

Hi, we have lived with our humidity-controlled heat recovery fans for 4+ years now and think they are great. Once they have dealt with excess activity generated humidity and move into trickle mode they are switched off. We do not run them 24/ 7 as they are not needed and during the warmer months, we just leave window open except at night time when insects are attracted to lights.

Interesting. I appreciate trickle mode for pre-warmed fresh air during the winter.
Agree windows can be opened in the warmer weather.
Good to have all these options and see which works for you.

Hi Lloyd Is your system whole house or are you using single room vents with heat recovery?

Hi, we have three single room vents with heat recovery- bathroom and kitchen.

1 Like

Thought it better to jump on this thread rather than start a new one. We’re looking for a single room heat recovery extractor for the utility room as there is a lot of heat generated by the tumble dryer that I don’t want to waste when it is in use. Our building inspector is telling us that the rate of extraction must be 30 litres per second and I’m struggling to find a HRU that will extract at more than 15 litres per second. Does anybody know, do they exist?

Welcome to the forum @the_rubik. I think 30l/s is going to be quite noisy. Do you know why such a high figure was specified?

Apart from fitting two 15l/s units at opposite ends of the room I don’t know how you could achieve that level of extraction.

So long as you are ok with the humidity going above recommended levels from time to time and then rapidly returning to normal I should think a high performance 15l/s system would be fine. You would also have to keep the room warm enough to avoid getting near the dew point, but the tumble drier probably does that for you.

(November 2022 price)

Hello @the_rubik, looking at the numbers I wonder if there is mix up with units? 10 litres/second is roughly equivalent to 30 meter cubed/hour. D

1 Like

Thanks for the reply Tim. So approved doc F of the regs states that the minimum intermittent rate (mechanical extraction) for a utility room is 30 litres per second. The continuous rate is 8 litres per second. My building control officer has quoted the first rate but I’m wondering if he’s got that wrong as I understand that heat returning units work on a continuous basis rather than the type of extractor fan that is connected to the light switch.

Yes possibly. That seems more realistic. The figure he’s quoted me is actually the litres per second figure (30 lp/s), I used a conversion tool (on a website) to do the arithmetic.

MVHR units work on a standby trickle plus boost as required, either manual or via sensor(s). I note that some forum members may cut the power completely to prevent trickle ventilation.

I recommend to use the trickle, particularly as that is when heat recovery is at its most efficient. Trickle ventilation alone would eventually clear bursts of humidity but you run a structural/aesthetic risk in the mean time if the humidity reaches near to the dew point. Mould doesn’t actually need condensation to grow as it can extract moisture from the air at high humidities. Therefore I also recommend using the boost when humidity exceeds 65% until in falls below 60%. Those are my own figures and not scientifically proven, although 60% is the recommended maximum domestic humidity. I know that many people trigger ventilation at 70% or above but I am a cautious individual.

My normal average extract humidity (whole house, trickle) is 49-51%

1 Like

This is the boost rate required for the extraction regardless of whether it is MVHR. I think that theoretically it could be less for MVHR as you are replacing extracted air with dry(er) warmed air but the regulations don’t recognise that.

1 Like