MVHR to replace trickle vents

[Fred D]

Hi everyone

 

We are remodelling our terraced house to create a larger kitchen space and to add a utility room. As part of the process we will be installing new sliding doors at the rear, and the type we have is frameless meaning that they do not have trickle vents. In addition, the utility room has no windows and therefore no ventilation. Lastly, we have a downstairs loo that was previously vented through the rear of the house - a route that is no longer available. 

 

My proposed solution is an MVHR system, with the caveats that this is only for a few rooms and that being a victorian house it's a bit leaky. My questions are:

 

 - is MVHR the best solution, or is there an alternative mechanical venting solution that is more fit for purpose?

 - if I go MVHR, am i better off using a branch solution given that i have incredibly limited access/space, and roof joists that pretty much all run in the least helpful direction

 - i need to extract from kitchen, utility and loo. If i have those 3 extraction points, can I then just supply into utility and kitchen, or even just one of the two?

 - Exhaust/Intake can't be through an outside wall as there isn't one accessible on the ground floor - any issues with exiting via a flat roof void and then vertical flue?

 

Thanks in advance for any assistance you can all provide

 

[Olf]

The conventional wisdom is that MVHR works the best in building of decent airtightness - and for that reason is necessary to begin with. But even in leaky places it will extract/supply where and when YOU want, not where and when draughts choose to be. However, as you are really after extracting only from 3 areas, it may be that extract fans will do the job just fine - either with a common flue or individually through the wall (or with some run of ducting before they can reach the wall, as it sounds is case of the loo). That will save you on MVHR unit purchase, space it takes and installation complexity (4 pipes + condensate drain). If you can go directly through the wall you could (especially in the case of the kitchen, due to large volume of air) look at a unit with heat recovery and you might get the best of both.

[Fred D]

13 hours ago, Olf said:

The conventional wisdom is that MVHR works the best in building of decent airtightness - and for that reason is necessary to begin with. But even in leaky places it will extract/supply where and when YOU want, not where and when draughts choose to be. However, as you are really after extracting only from 3 areas, it may be that extract fans will do the job just fine - either with a common flue or individually through the wall (or with some run of ducting before they can reach the wall, as it sounds is case of the loo). That will save you on MVHR unit purchase, space it takes and installation complexity (4 pipes + condensate drain). If you can go directly through the wall you could (especially in the case of the kitchen, due to large volume of air) look at a unit with heat recovery and you might get the best of both.

Olf - many thanks for your thoughts. If i sort out the front door, once this work is complete the ground floor will be pretty airtight - we are on 3 floors but every window is a replacement double glazed unit. Biggest source of air leakage will be the loft spaces. 

One of the requirements for replacing trickle vents is 'always on' so that there is a background constant replacement of air - are there standard extractors that function this way? You mentioned single room MVHR for the kitchen, which was my original plan, but there is quite literally no external wall to accommodate a flue. I couldn't find a single room MVHR unit that can vent vertically through a flat roof - do they exist?

Thanks again

[Olf]

It sounds like the layout may force you to go MVHR - maybe check the kitchen unit options?

This is what I used last time: VTC Low-E  - it is so-so, but the price was attractive. I had it hanged in upstairs airing cupboard so it could serve the bathrooms and deliver to the bedrooms - it definitely helped with the bathrooms, misus tested the boost every time and it would clear the sauna quickly. Even in the bedrooms with leaky windows it made noticable difference, with no stale smells in the morning and much reduced condensation. For intake/outlet I just used the roof vents on the opposite sides of the roof All branched, no silencer (but pipes laid to not to cause crosstalk) etc.

Of course you can fit it in the kitchen, you will gain extraction point and maybe ever replace the hood as they are intended to do.

[Fred D]

9 minutes ago, Olf said:

It sounds like the layout may force you to go MVHR - maybe check the kitchen unit options?

This is what I used last time: VTC Low-E  - it is so-so, but the price was attractive. I had it hanged in upstairs airing cupboard so it could serve the bathrooms and deliver to the bedrooms - it definitely helped with the bathrooms, misus tested the boost every time and it would clear the sauna quickly. Even in the bedrooms with leaky windows it made noticable difference, with no stale smells in the morning and much reduced condensation. For intake/outlet I just used the roof vents on the opposite sides of the roof All branched, no silencer (but pipes laid to not to cause crosstalk) etc.

Of course you can fit it in the kitchen, you will gain extraction point and maybe ever replace the hood as they are intended to do.

So you went branch not radial? I think that would help me by reducing the number of pipes in a very confined space including not needing a manifold. 

[Olf]

Knowing what I know now I'd probably go radial, but branch worked ok and was way cheaper. A lot depends on the layout/joists directions etc - mind I routed everything through the loft, downstairs loo was a straight run down, so all relatively easy.