If the downstairs toilet is just a toilet without a shower/laundry/drying room I cannot see that a freestanding single room MVHR could be economical to buy or run. It only makes sense if it can be combined with another MVHR or other services in the room.
Thanks so much for your responses.
Itâs a 4 bed Edwardian Semi - 1914 build. We have Ventive - a passive ventilation system, which has ducts in all dry rooms but neither of the bathrooms, so weâre not really looking for a whole house system.
The main issue is high humidity levels throughout the house, but particularly in the upstairs where the main bathroom is. We do have a basic extractor fan, but weâre considering upgrading it to a heat recovery fan. The downstairs bathroom is a toilet and washing machine. Itâs also where the boiler is. It has a broken extractor fan, which we need to replace. The window in there is sealed and cannot be opened.
The upstairs and downstairs bathrooms are in different places so I doubt a dual room extract would work.
We bought a Meaco dehumidifier a couple of weeks ago and have been running it continually since then.
Ah yes, passive stack ventilation. It was very popular when first released and the theory of the physics was explained but the truth is that it doesnât work reliably. It is no longer in the list of approved ventilation systems in Building Regulations.
As you have ducts in place you are well on the way to getting a whole house ventilation system installed without most of the upheaval.
The structure of your house is probably very similar to @pottyone72âs Victorian semi, so I suggest searching the forum for some of her posts.
Returning to the immediate ventilation/humidity issues, the upstairs rooms without ducts can relatively easily have them added if you go for a system upgradable to full house in the future.
My own preference, based on advice from both the AECB and the Passivhaus Trust, is full time whole house ventilation with a boost facility for particularly damp or smelly events. My own house has a quality MVHR, despite not being fully airtight.
For downstairs I hope that the kitchen has an extract, either by cooker hood or through the wall. If you have a recycling cooker hood and no extract, cooking could account for most of your humidity.
The downstairs toilet/utility room probably needs ventilation both for when the laundry is taken out of the machine and for toilet smells. Unless fresh air from a single room MVHR can be directed into an adjacent room (creating a 2 room clean air system) it probably isnât worth a single room system. You are unlikely to recover enough heat in the systemâs life to cover the purchase price.
A decent whole house MVHR system is pricy but compared with the cost of multiple single room systems and comparing efficiencies, they are good value.
If you are dedicated to the single route you will need 3 systems. Upstairs bathroom, downstairs toilet etc and kitchen. Also, optionally, the room where you dry clothes in winter or other wet days.
Please donât remove your existing ducts. If you donât need them now then blank them off so that they can be re-utilised in the future with negligible disruption.
By the way, my experience of Meaco is good.
So Iâve not purchased the Kair model of single room heat recovery yet. It sounds like weâre in similar positions @Laura_Gilchrist ⊠We also have plumbing issues, from a leaking wetroom we had to tear up and dry out.
Our current conundrum is âhow to fit the shower tray under the exixting wall tilesâ ⊠We have a Wedi tile backer board system which is a good insulator, but if damaged could become problematic . We need to remove or cut the bottom tiles so the tray can slot under. Then we can retile and seal down to the tray.
We already have a 10cm hole for our existing vent , the Kair SRHR needs a 15cm hole cutting with a 1cm downslope to the outside. It is slow progress making these decisions , yet so important understand and ensure the little details are right to avoid problems
Iâll keep you updated.
Thanks so much for your response!
Yes we have an extractor hood over the cooker which is vented to the outside. We also have a continuously operating v low speed trickle fan in the kitchen, which is supposed to help boost the effectiveness of the Ventive system.
The 2 room clean-air system is a good idea because the downstairs toilet is right next to the kitchen. Would this deal with the humidity issue too?
I hadnât thought about the fact that weâre halfway there to a full MVHR. We only - reluctantly - replaced our boiler a year ago because when I looked into MVHR it became clear that because our house isnât thermally sealed, it wouldnât provide enough heat. (Weâve looked into external wall insulation but itâs always been prohibitively expensive for the scale of our home).
So do you have an MVHR on top of a standard central heating system? Iâm also wondering - of course - what the cost of running such a system would be electricity wise?
Sorry, lots of questions from me!
@pottyone72
Thanks for sharing! You sound like youâve got your hands full there! I donât know about you, but to me it feels like a moving jigsaw often. Yes please do keep us all updated.
@Laura_Gilchrist, in brief, âyesâ and ânot muchâ. Now for more detail.
MVHR operates independently of any heating system and my heating happens to be gas, with radiators. It happens that my gas heating operates at 45°C most of the time but that doesnât effect the ventilation.
I donât have wall insulation or cavity walls. My house was built in 1936 and is probably one of the last solid masonry houses built in the UK. I do have treble glazing and a new warm roof. Under the ground floor is some pretty ineffectual insulation.
I fitted my first MVHR 17 years ago. It had a declared efficiency of 82% but I doubt that it ever achieved that. It lasted 12 years and by then I couldnât get replacement parts. I have now bought a Passivhaus certified Zehnder ComfoAir Q350. With minor modification I fitted the new unit to the existing ducts. The improvements in the intervening years are amazing. Efficiency is independently certified as 95% and it is totally silent. The associated app shows the temperature and humidity of air drawn in, conditioned air going into the house, extracted air from wet rooms and air exhausted back into the atmosphere.
I have my MVHR plugged into a smart socket and can view how much electricity it user. Normally it draws 35W but on boost it reaches 47W.
You may notice that the air entering the house and the air being extracted are the same temperature. That means that my heating and heat losses are balanced.
The humidity, on the other hand has increased while the air is passing through the house, so the house is being dried, and is not in equilibrium. My explanation is that I had clothes drying in the wet room.
Wow this is all so helpful. Thank you.
Totally silent is quite incredible and those running costs are impressive too - our Meaco dehumidifier by comparison is 255W!
It sounds like it would be totally worth it, if we could stretch to it.
Would you be willing to share a bit more about what it cost to buy and then install your system?
And also how easy/hard was it to find someone who knew what they were doing and you trusted?
I really appreciate all this incredible help.
I used Green Building Store because of their reputation. As luck would have it they also offer a discount to Carbon Coop members.
They will want every measurement of your house that you knew existed and a floor plan. If you have a basement or large enough utility room they will probably design a system with the unit down there. In my case the unit is in the loft. I bought a cheap winch to help get it up there. The winch was only about ÂŁ30. The unit was seriously more at ÂŁ1974 with Carbon Coop discount of 30% plus VAT. You will probably need to get more ducting, airproof joining tape and louvres as well. I didnât need to pay for layout design as I was just using the existing ducts.
I have a larger than average loft hatch. A totally airtight and well insulated Wellhöfer. Also from Green Building Store and bought with the installation of equipment in mind.
Thanks. Great to know that the Green Building Store offer a discount to members, I didnât know that.
We donât have a basement to so yes it would be in the loft, which is where the ventive ducts are currently.
Did you install the system yourself?
The original system, 17 years ago, was installed as an extension was being built and followed a professionally prepared layout included in the purchase price. Much of the ductwork was built into partition walls or built in wardrobes. This was done by the builders, not professionally.
The replacement system I installed myself, including changes to the termination of ducts to fit the new unit. I did, however, have the system balanced professionally according to the airflow per room table supplied by Green Building Store for a smallish fee. I never had similar balancing for the old system.
The unit needs to remain accessible for changing air filters. I had originally planned to move the unit down into the living area to make filter changes in my old age easier but when I measured up there wasnât anywhere it would fit. This is a frequent problem when the MVHR is retrofitted. In a new build space can be allowed for accessible access.
The unit is now just under a metre from the hatch with a boarded area in front of it. Changing the filters is really easy, unlike my old system.
Thank you for the details. Great point about ease of changing the filters, thatâs definitely an important consideration.
Weâd definitely need to pay someone to install ours as neither of us is that handy!
Sounds like the Green Building Store were really helpful in all of this.
Iâve just looked and Green Building Store DONâT offer a discount to Carbon Coop members (any more?).
There is a work round to get a discount. GBS do offer a discount to AECB members and membership of the AECB is free to Carbon Coop members, so with a little forward planning the discount is available to all Carbon Coop members.
Decisions âŠdecisions!! 
For our bathroom single room heat recovery ventilation unit, we narrowed it down to two choices from Kair. I put some of the obvious differences below with links to each. (Iâm definitely novice in these comparisons).
Energy efficiency, alongside effective drying of laundry in the bathroom is the main consideration for us.
The Kair K-HRV150 - needs a larger 150mm duct hole drilling around the existing 100mm hole, yet this model extraction/heat recovery is up to 84% and retails at only ÂŁ286.
https://www.kair.co.uk/product/kair-heat-recovery-room-ventilator/
The Kair lo-carbon tempra HTP - this one will fit the existing 100mm duct width , which we already have for the existing extractor fan, but the extraction rate is only up to 64% and the product retails at around ÂŁ350
https://www.extractorfanworld.co.uk/vent-axia-443311-lo-carbon-tempra-htp-heat-recovery-unit-humidistat-timer-pullcord-1141-p.asp
Talking to our electrician about making an existing ducting hole bigger, he said itâs more temperamental than if you were starting a hole from scratch. Heâs suggested refilling it if we want the larger hole drilling in the same place.
Any advice or thoughts would be greatly appreciated.
150mm one because itâs a bigger heat exchanger.
A few stacked layers of scrap ply wood cut to 100mm diameter, plugged then foamed or wedged in place could act as a pilot hole guide. I reckon the sparky would have a go at that.
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@Frank_Reif is right. The wall drill needs to have solid material to cut through at the centre of the proposed hole. Whether there are any smaller voids in between is not important.
I know it doesnât apply to you but readers with cavity walls should seal the cavity before fitting the MVHR. In all cases, the duct, once installed, also needs sealing to the wall all round at each end. If you are going to have any air leakage please avoid having it near the MVHR unit.
I also nominate the 150mm unit.
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Just want to say how much I appreciate this forum and itâs members.
We really are a people powered community.
Thankyou @cc_staff and all the @cc_members in our forum community.
You have enabled me to make good informed choices that I feel confident about for my home. 
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A slightly tapered 2x4 wedged across the diameter might be better. If you want to use the same centre you could use a 100mm bit to mark the pilot, before using that pilot to start the 150mm hole.
You could also take this opportunity to move it slightly over if you have clearance issues.
I bought the Kair K-HRV150 recommended here in the forum.
Just need to install it now !!
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Ooh exciting @pottyone72 ! Let us know how you get on with it.
On the advice of @Tim_Gilbert Iâm considering a system vented to two rooms since our downstairs toilet and kitchen are adjacent. Just need to figure out whatâs possible now! Still doing the research.
That is a bold step made. Are you planning to find a way to widen your current vent or are you doing to start again, filling in the old 100mm opening?