MVHR installers or alternatives?

[Swampy]

Hi, 

 

Currently in the middle of renovating and extending our 1950s semi and I need some advice on ventilation. 

 

Without going into too much detail at this point, I'm aiming to make the house very well insulated and as airtight as possible (I'm aware of the limitations of doing this in a refurb, but about 85% of external walls will be new in the end). 

 

Humidity is currently an issue in the house and with improved airtightness, I only expect that to get worse, so I was planning to install an MVHR system, however, due to ceiling height, RSJ locations and floor joist orientations, MVHR doesn't seem viable - I don't want boxed-in sections running along the ceilings all over the ground floor. 

 

I know someone who has a PIV system installed, but they confirmed what I'd read - they have a significant cold spot during the winter, where the fresh air is coming in. 

 

I'm not keen on the small, individual, 'per room' MVHR units either, as I have concerns about noise and their general heat recovery efficiency. 

 

What other options are there? I'm really struggling to find anything which will definitely work! 

 

I'm also open to getting an expert round to assess the suitability of the house for MVHR, in case I've misunderstood how the ducting could be routed, but I'm in a catch 22 situation - I have to pay for a design first, yet I won't know until after that if it's appropriate for my home (as I've said, I don't want lots of boxed in sections running across ceilings in main living areas). 

 

If anybody could recommend an MVHR installer local to east Berkshire, that would be great. 

Thanks. 

[JohnMo]

Why limit yourself to MVHR, dMEV or MEV done well can be equally effective.  You need to it on a humidity controlled basis, with humidity activated inlets, either trickle or through wall.

 

The other option is cascade MVHR, very little ducting used, which is a little like PIV and MEV combined with heat recovery 

[Iceverge]

9 hours ago, Swampy said:

85% of external walls will be new in the end

 

Have you considered a knock and rebuild. replacing 85% of the walls will take longer and cost more than a new house. 

[Swampy]

3 hours ago, JohnMo said:

Why limit yourself to MVHR, dMEV or MEV done well can be equally effective.  You need to it on a humidity controlled basis, with humidity activated inlets, either trickle or through wall.

 

The other option is cascade MVHR, very little ducting used, which is a little like PIV and MEV combined with heat recovery 

 

Thanks for the suggestions - I'll investigate further. 

 

Do they have heat recovery and they ever used in enerphit projects? 

 

[Swampy]

1 hour ago, Iceverge said:

 

Have you considered a knock and rebuild. replacing 85% of the walls will take longer and cost more than a new house. 

 

We're extending to the back, side and partially at the front, so some existing external walls are being removed and some are becoming internal walls. 

 

Knock down and rebuild was not an option, based on the fact that it's semi-detached and the build costs we were quoted for the work as it is, were exorbitant. 

 

Fortunately, we did find someone and the work is already well underway.  

 

Edited February 2, 2024 by Swampy

[Iceverge]

dMev in that case. 

 

Any noise will be in kitchens, utilities and bathrooms so not critical. 

 

 

[JohnMo]

2 hours ago, Swampy said:

 

Thanks for the suggestions - I'll investigate further. 

 

Do they have heat recovery and they ever used in enerphit projects? 

 

Cascade MVHR yes. 

 

5 hours ago, JohnMo said:

dMEV or MEV

No heat recovery, but do not exchange air when not needed or do so at a minimum rate. Tickle vents open and close based on humidity levels.

[Swampy]

I contacted a company which sells cascading MVHR systems, but they said it's not intended for a house like ours - rather it's for apartments and small homes. 

 

So it looks like heat recovery is not going to be an option. 

 

Looking into dMEV and MEV next. 

[JohnMo]

13 minutes ago, Swampy said:

contacted a company which sells cascading MVHR systems, but they said it's not intended for a house like ours - rather it's for apartments and small homes.

You can still use the same principles of cascade with a normal MVHR unit.

[Swampy]

Late coming back to this, but I’ve completely ruled out centralized MVHR now, as there’s just no way to fit it in without boxing in most of the ducting, which I don’t want to do.  
 

So the options left are to use trickle vents, DMEV or decentralized MVHR. 
Both these systems appear to be fairly similar, in that they use individual, smaller units distributed around the house, but DMEV doesn’t do heat recovery. 

I need to order windows very soon, so it’s crunch time. 

Anybody have any thoughts on the two systems and if one is preferable to the other? 

 

I also have concerns about how much heat we’ll lose through the units, as well as potential noise issues from outside. 
 

Thanks! 
 

 

 

 

[JohnMo]

3 hours ago, Swampy said:

decentralized MVHR

You need dMVHR in every room to be effective, so gets expensive.

 

dMEV cheap as chips, costs buttons to run and buy. Only fans in wet rooms. You really need decent trickle vents that active on humidity or are self regulated.

[Swampy]

5 hours ago, JohnMo said:

You really need decent trickle vents that active on humidity or are self regulated.

I meant trickle vents on windows, which I’d been hoping to avoid on the new windows we’ll be ordering. 
Do you mean something else? 
 

Yes, DMVHR units do seem to be pretty expensive. 

Edited April 9, 2024 by Swampy

[MikeSharp01]

On 02/02/2024 at 00:28, Swampy said:

I don't want lots of boxed in sections running across ceilings in main living areas). 

Can you make a feature of the pipes. In a new build, yes it was a new build so perhaps more possible, I was the end user for we decided to have all the services on show everywhere we could. 

[JohnMo]

7 hours ago, Swampy said:

trickle vents on windows, which I’d been hoping to avoid on the new windows we’ll be ordering. 
Do you mean something else? 

I do mean trickle vents vents in windows, but not the normal rubbish 50p version they suppliers normally install. 

 

You can get self regulated ones that only as much as required and also have them with incorporated noise attenuation. Or you can ditch the window trickle vents and do through wall vents.

 

dMEV is designed to cross ventilate, so you need to have under cuts on all doors also 

[Strak]

On 09/02/2024 at 17:04, JohnMo said:

You can still use the same principles of cascade with a normal MVHR unit.

I know it's quote old now, but this thread caught my eye, and specifically the idea of cascade with normal MVHR unit. I'm also looking at a retrofit, figuring out if ducting is possible, but there are definitely tricky areas.

 

Do you have any suggested reading material or companies to look at JohnMo? A guess on the name of it - is the idea that I would have MVHR to some locations, and then ventilation between rooms where it's too difficult to get a duct from the MVHR unit?

[JohnMo]

Brink do a system based around a normal MVHR unit. Basically they dump the supply air in the hall, similar to PIV supply only system. You do need to duct and extract from wet rooms. And depending on room layout you may need internal fans or if routing allows duct to some dry rooms.

 

I read about it first on Passivhaus website. But search for cascade ventilation or cascade ventilation with heat recovery.

 

You main thing you need to do is visualise where and how air moves about the house to make sure all areas are covered.

[Nickfromwales]

1 hour ago, Strak said:

I know it's quote old now, but this thread caught my eye, and specifically the idea of cascade with normal MVHR unit. I'm also looking at a retrofit, figuring out if ducting is possible, but there are definitely tricky areas.

 

Do you have any suggested reading material or companies to look at JohnMo? A guess on the name of it - is the idea that I would have MVHR to some locations, and then ventilation between rooms where it's too difficult to get a duct from the MVHR unit?

I’ve just done an MVHR retrofit in quite a large, 3-storey residential home, and you’d be surprised how you can blend a radial system in to an existing house.

 

You can use multiples of smaller bore ducting to replace one larger one, for eg, with duct sizes down to 50mm, 75mm (and 92mm being the largest you need for radial). No need for rigid 100/125/150 etc, as all the big bore stuff is at the unit only.

 

 

Two left ducts were fresh and exhaust to atmosphere. Right hand pair dropped under the unit via 2x acoustic attenuators to the manifolds. 
 

 

And that was all in a very compact cupboard space. 

This is 3x 92mm ducts, soon to be boxed, plastered and painted to allow them to blend in. 

 

Transfer grilles are a great way to cheat out of getting a duct to a particularly problematic space, but the caveat is needing higher flow rates in the room that is then sucking or blowing through two.

 

Oversizing the unit is good advice too.

 

It’s doable if you get someone with a bit of an engineering based brain and some tenacity. 

[Strak]

17 hours ago, JohnMo said:

Brink do a system based around a normal MVHR unit. Basically the dump the supply air in the hall, similar to PIV supply only system. You bo need to duct and extract from wet rooms. And depending on room layout you may need internal fans or if routing allows duct to some dry rooms.

 

I read about it first on Passivhaus website. But search for cascade ventilation or cascade ventilation with heat recovery.

 

You main thing you need to is visualise where and how air moves about the house to make sure all areas are covered.

 

Thanks. I also just found this site which had a video that explains the principles, with some very fancy animation: https://www.paulheatrecovery.co.uk/mvhr-and-ventilation-products/blumartin-freeair100-demand-controlled-cascade-mvhr/

That seems to have intelligent vents in each room to control what is flowing where. The website has a couple of retrofit solutions, but both look to be for smaller properties. I'll keep digging on this.

 

16 hours ago, Nickfromwales said:

I’ve just done an MVHR retrofit in quite a large, 3-storey residential home, and you’d be surprised how you can blend a radial system in to an existing house.

 

You can use multiples of smaller bore ducting to replace one larger one, for eg, with duct sizes down to 50mm, 75mm (and 92mm being the largest you need for radial). No need for rigid 100/125/150 etc, as all the big bore stuff is at the unit only.

 

It’s doable if you get someone with a bit of an engineering based brain and some tenacity. 

 

Thanks - that's encouraging. I actually do think it would be possible but architect is skeptical. I have the tenacity, half an engineering brain but two kids so not quite enough time to plan it all out properly! We're about to have a bunch of work done around the property which will involve lifting floorboards everywhere and replacing loft joists which is the ideal time to do it. I'm trying to figure things out before that work starts, and running out of time.

 

Two of the rooms have unused chimney breasts (all to be sealed up) and I'm wondering if they would be suitable for running the ducting down. I think an issue there would be that the temp inside the chimney would be much cooler than the rooms of the house which will be internally insulated. Plus I'm not sure how feasible it is to get ducting down a chimney breast and back out where I want it to go.

 

16 hours ago, Nickfromwales said:

Transfer grilles are a great way to cheat out of getting a duct to a particularly problematic space, but the caveat is needing higher flow rates in the room that is then sucking or blowing through two.

 

Oversizing the unit is good advice too.

Does a transfer grille mean this sort of thing https://www.safelincs.co.uk/fire-rated-intumescent-air-transfer-grilles/?sku=PPATGFPS2251&ppcGeneral&gad_source=1&gad_campaignid=21280659513&gclid=Cj0KCQiAo4TKBhDRARIsAGW29bdZzDnAdMJjg83hpn7cdlyOtgRQ9K3vlmmxJCyJPmaZLv_X3QbmujYaAun1EALw_wcB where I can only get a duct to one room? Duct to that room, then transfer grille into the next room to allow airflow? Sounds like the principle of a cascade system, which I think could suit me well.