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Well, it's the 5th Oct and I've fired up our upper & lower floor dehumidifiers. Pulled 3ltrs of water between them in about 8hrs.

We have switched to a fair amount of indoor drying the past few days so thought it prudent to be yon.proactive way.



I had thought the other week about fitting a single point mhvr or whatever they're acronym is. Which led me onto thinking of retrofitting a cooker hood? Is that even a thing? We have 3 bathroom fans and a cooker hood, surely I can take advantage of existing ducting?

I have done quite a bit of digging into MVHR (Mechanical Ventilation Heat Recovery) and the ducting is the main issue with retrofitting (i.e. getting it to where it needs to go)

Typically you need a balanced in and out flow - from what you have described you have all out flowing points.

From what I have read you have outflow from all damp areas (kitchen, bathrooms, utility rooms) and inflow to dry areas (bedrooms, living room, dining room) and for a centralised system there is quite a bit of balancing to do.

As our new wet room is not on an outside wall we are installing a small standalone unit that has an out flow from the bathroom through a heat exchanger and an inflow that vents into the bedroom.

There are companies out there that will design a system for free from floor plans - based on you buying the equipment from them.

It is quite a big task from what I have seen so far. I don't know about using the kitchen hood extractor.

All of our extractors were switched over to dMEVs with smart humidistats by the previous owners eco work.

They work well, but we obviously lose heat from them.
I had thought that a MVHR system would solve my fresh air on face issue whilst sleeping, but as cojmh says its hard to retrofit... though must be easier in a bungalow?!

Be interested in banging heads together for the cooker hood.
Ours is a useless recirculating filter thing, and we have a dMEV on thr opposite side of the kitchen. I had also wondered if i could link the two somehow to take advantage of the vent, but would likely involve ducting or drop ceilings to do so.

However, i do know there are individual heat recovery units that can be swapped out for normal extractors.
These would do a similar thing to a full MVHR, but much easier to retrofit with existing fans.

NoraBatty wrote: ↑Sat Oct 05, 2024 11:35 pm All of our extractors were switched over to dMEVs with smart humidistats by the previous owners eco work.

They work well, but we obviously lose heat from them.
I had thought that a MVHR system would solve my fresh air on face issue whilst sleeping, but as cojmh says its hard to retrofit... though must be easier in a bungalow?!

Be interested in banging heads together for the cooker hood.
Ours is a useless recirculating filter thing, and we have a dMEV on thr opposite side of the kitchen. I had also wondered if i could link the two somehow to take advantage of the vent, but would likely involve ducting or drop ceilings to do so.

However, i do know there are individual heat recovery units that can be swapped out for normal extractors.
These would do a similar thing to a full MVHR, but much easier to retrofit with existing fans.

Good point on the heat exiting the building on a 1 way journey. At least with a dehumidifier it's retained. In saying that I think i'll have a crack at a dehumidistat fan in the downstairs bathroom, central in the house and close to kitchen. Down to 1ltr per day extraction and humidity set at 55%. Much & many wash loads being run through post holiday.

Watch out for the single point MVHR units t he plastic sleeve contains the heat exchanger and wall thickness needs to be considered as it has min/max sizes we fitted one recently that as specified, needed a seperate controller/power supply that we hadn’t allowed for, was a pain to fit in a metal skinned wall…….

Joeboy wrote: ↑Mon Oct 07, 2024 8:31 am
Good point on the heat exiting the building on a 1 way journey. At least with a dehumidifier it's retained. In saying that I think i'll have a crack at a dehumidistat fan in the downstairs bathroom, central in the house and close to kitchen. Down to 1ltr per day extraction and humidity set at 55%. Much & many wash loads being run through post holiday.

We do a similar thing in the conservatory over winter. i put one of those very old style pulley airers/ sheilas maids up to hang high up on some gallows brackets and take advantage of the ceiling height in there.
Had one in the last house and was told i must be at least 110 yrs old to even know what one was.
Leave the dehumidifier on all night and its guaranteed bone dry in the morning without the need for heating. Marvellous.

On the rare occasions we had the dehumidifier on in the lounge last year, the humidity dropped under 60 and we then had to deal with some vicious static shocks every time the cats came in the room wanting a cuddle.

Of course its getting run a bit more often now. Whenever it rains with strong wind. Turns out the solar flashings are lifting up and letting water in, as they also werent installed properly. Again, awaiting remediation works.

cojmh wrote: ↑Sat Oct 05, 2024 11:19 pm I have done quite a bit of digging into MVHR (Mechanical Ventilation Heat Recovery) and the ducting is the main issue with retrofitting (i.e. getting it to where it needs to go)

Typically you need a balanced in and out flow - from what you have described you have all out flowing points.

From what I have read you have outflow from all damp areas (kitchen, bathrooms, utility rooms) and inflow to dry areas (bedrooms, living room, dining room) and for a centralised system there is quite a bit of balancing to do.

As our new wet room is not on an outside wall we are installing a small standalone unit that has an out flow from the bathroom through a heat exchanger and an inflow that vents into the bedroom.

There are companies out there that will design a system for free from floor plans - based on you buying the equipment from them.

It is quite a big task from what I have seen so far. I don't know about using the kitchen hood extractor.

We have a whole-house MVHR system just for the first floor which was designed by Villavent from our floor plans. They did a materials takeoff from that for all the ductwork and connections. IIRC they are based in Norway but now called SystemAir UK. Our loft is full of 6 in ducting for the main runs and 4 in for the individual drops.

They do not recommend connecting a cooker hood (or tumble dryer) bc of the grease and fluff, but we do have an self-closing (fire) extract point in the kitchen above the AGA. We cut DIY filters out of fire-retardant BAF sheet (upholstery wadding) to collect the grease from the kitchen and towel fluff from the bathrooms, they need changing every 3 and 6 months respectively and keep the duct work and heat exchanger nice and clean. There are then supply points in all the bedrooms.

We also had a damp bedroom wall which we dry-lined with 50mm of sheep's wool insulation and a 50mm cavity which is vented from the room at the bottom and has an extract vent to the MVHR at the top, this keeps the wall free of damp and works well.

Its operation is barely noticeable on Normal fan speed and even quieter on Low. Have modified the controls so that fan speed is increased by one step whenever any of the bathroom lights is switched on with 8 mins over-run.

I have no idea of the efficiency gains but the primary driver was the need to sort out the damp wall and the previous bathroom extractor fans which all vented into the loft space not the outside(!)