MVHR, PIV or just a bathroom fan?

[Oldgreybeard]

That's not sort of help I was hoping for. I thought you would convince me to go with extraction fans
Have you guys done it yourself of used someone for installation/calibration. I'm happy to pay but I don't have any positive experience recently with delegating work I'm afraid, so I guess I would need to do it myself.

Perhaps there is a good online shop doing lots of work to workout what the client needs to supply a proper DIY kit.

Mine was a DIY install, but was a new build, so duct runs were easy, all done before the walls and ceiling were plasterboarded. I got some things right straight off, like mounting the MVHR on anti-vibration mounts to reduce fan noise transmission to the floor it's mounted on, and I got the flow calculations right, so the system wasn't that difficult to balance.

The one thing I got wrong was omitting silencers on the MVHR room supply and extract ducts. They made a big difference to the noise level and made the system effectively inaudible unless it's boosting.

Nothing about the installation is at all difficult, easier with two pairs of hands, perhaps, as feeding ducting around on your own can be a bit tiresome. Hardest bit was flow balancing. I used a hot wire anemometer to measure the flow rate, poking it into a bit of 150mm pipe held tight to each ceiling fitting. Balancing was still a lengthy process though. It's very iterative, adjust one fitting a lot and that changes the back pressure and throws all the others out.

[marshman]

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[Oldgreybeard]

Nothing about the installation is at all difficult, easier with two pairs of hands, perhaps, as feeding ducting around on your own can be a bit tiresome. Hardest bit was flow balancing. I used a hot wire anemometer to measure the flow rate, poking it into a bit of 150mm pipe held tight to each ceiling fitting. Balancing was still a lengthy process though. It's very iterative, adjust one fitting a lot and that changes the back pressure and throws all the others out.

Glad I'm not the only one that had to "scratch my head" when it came to balancing the "suck n blow" between rooms

I had a spreadsheet on my laptop as I was doing it, with a column for each set of room readings. I'd adjust one to get it right, then go around measuring all the others, only to find they had all changed, so then adjusted them all very slightly, only to find that the one I'd got right now wasn't!

Took longer to get it balanced than it did to install all the ducting.

Only good thing about it was that the building inspector was happy with the home-made certificate I'd produced showing compliance with the regs.

[Stig]

If you want to do a lot of DIY
https://camelot-forum.co.uk/phpBB3/view ... f=21&t=463

I've seen it and, nope, that's not the route I'm keen to take .

I don't blame you! If it hadn't been for lockdown and needing to keep my mind off COVID worries it would probably have remained just a thought experiment.

Does it make much difference if i initially do MVHR for upstairs only and add downstairs later on? Is it just extra ducting that is required and making sure the unit itself is fit for this, or is there anything else I should be worry about?

I don't see why not if you fit manifolds/Y-pieces with the unused ports sealed off and keep the fan speed low until you add the downstairs ducts (and then re-balance). I assume commercial units just have the 4 ports on the heat exchanger and splitting/combing is done on the ducts.

[marshman]

Does it make much difference if i initially do MVHR for upstairs only and add downstairs later on? Is it just extra ducting that is required and making sure the unit itself is fit for this, or is there anything else I should be worry about?

I don't see why not if you fit manifolds/Y-pieces with the unused ports sealed off and keep the fan speed low until you add the downstairs ducts (and then re-balance). I assume commercial units just have the 4 ports on the heat exchanger and splitting/combing is done on the ducts.

All the commercial fan units I have used have just the four ports but I have seen some with multiple outlets.

Nothing stopping you just doing the top floor and adding the lower floor later, I'm not sure how much benefit you will get apart from decent extract from the bathroom. If you spec the fan unit to do the whole house then it will be over specced for just the first floor so as Stig says you will have to keep the fan speed quite low, you will possibly need a speed controller for the motors to limit the top speed.

[Oldgreybeard]

Does it make much difference if i initially do MVHR for upstairs only and add downstairs later on? Is it just extra ducting that is required and making sure the unit itself is fit for this, or is there anything else I should be worry about?

I don't see why not if you fit manifolds/Y-pieces with the unused ports sealed off and keep the fan speed low until you add the downstairs ducts (and then re-balance). I assume commercial units just have the 4 ports on the heat exchanger and splitting/combing is done on the ducts.

All the commercial fan units I have used have just the four ports but I have seen some with multiple outlets.

Nothing stopping you just doing the top floor and adding the lower floor later, I'm not sure how much benefit you will get apart from decent extract from the bathroom. If you spec the fan unit to do the whole house then it will be over specced for just the first floor so as Stig says you will have to keep the fan speed quite low, you will possibly need a speed controller for the motors to limit the top speed.

I agree, I've only ever seen units with four ports. Ours has four ports, an external air intake, external air exhaust, internal air supply (to the habitable rooms) and an internal air extract (from bathrooms, kitchen, WC and utility rooms).

I did opt to use a radial duct system though, and would suggest that this might be an easier option to both fit and balance. This has two plenum chamber/duct connection boxes, that look like this:



These can be fitted anywhere that's convenient and connected to the MVHR unit with a large diameter duct (usually 150mm or 160mm diameter). The advantage of this is that there is supposed to be less interference between duct runs when balancing, although there is very definitely still some I found. Main advantage I found was that it just made running the ducting a great deal simpler, as I didn't have to think about leg lengths, duct flow velocity, etc.

A radial duct system would also lend itself well to doing one floor at a time, I think, just blank off the unused ports on the plenum until they are needed.

[martinW]

Just throwing in a curved ball here.

Dehumidifier....

We have one in our landing and leave the bathroom door open. It work well and pick up a lot of water and also heats the rooms a little bit.

I always intended to install it in attic and duct the air outlet back to bathroom.

Never got around to it in 3 years.

Fed up of in wall fans failing, so would only now use an inline one.

[Oldgreybeard]

Just throwing in a curved ball here.

Dehumidifier....

We have one in our landing and leave the bathroom door open. It work well and pick up a lot of water and also heats the rooms a little bit.

I always intended to install it in attic and duct the air outlet back to bathroom.

Never got around to it in 3 years.

Fed up of in wall fans failing, so would only now use an inline one.

We sometimes use our MVHR as a dehumidifier. Not too often, as it tends to make the air a bit too dry, but very useful in short burst when it's very damp and we want to dry clothes indoors, without using the tumble drier ( a useless condensing thing that takes forever). The MVHR also has a heating function (it has a small built-in reversible air-to-air heat pump), but we've never used that, either, mainly because the thermostat programmer thing for it has an almost indecipherable manual.

Might give it a go, though, as when its small heat pump is running it only draws about 500W, roughly half the power the big heat pump draws when running. It may be better suited to a bit of top up heat when running on battery power, perhaps. Might also have a faster response time than heating tonnes of concrete in the floor. I do know that it draws a lot of water out of the air, as whenever we've run it in dehumidifier mode I can hear the water trickling down the drain that's at the back of the downstairs airing cupboard.

[Oldgreybeard]

As an addendum to the above, I turned the MVHR heat pump on just after making that post. It's drawing about 500W from the batteries and in the space of a few minutes has made a very noticeable difference - the temperature in my study has risen about half a degree! Amazing, I would never have imagined it could be so effective. I've just poked the IR thermometer up the fresh air feed to my office and it's reading 44°C, so right now it's like the house having 6 small fan heaters running (we have fresh air feeds to 6 rooms).

Perhaps I should have played around with this before now, just never really occurred to me, as we didn't buy this particular MVHR because it had this small integrated heat pump. Only downside seems to be the outside noise, there is a distinct fan noise coming from the MVHR intake and exhaust terminals. Not objectionably loud, but noticeable as they are normally silent.

I will have to turn it off in a minute, or else we are going to cook, but nice to know we have enough backup heating from it if the main ASHP ever falls over.

[MrPablo]

Hi OGB, what MVHR do you have out of curiosity?
I'm starting to plan some more house refurb projects for next year and this is on my list.