Interested in DIY UFH and MVHR

[iansr]

Hi, we are remodelling a dormer bungalow by adding a substantial full width single storey extension at the rear of the property and creating an entirely new first floor / roof over the existing structure.  I would like to have wet UFH throughout the house and also MVHR.  I am looking into partially DIYing the installation of both systems in order to save money.   Originally we were planning on having an ASHP but we will not make the March 2022 RHI deadline and so instead we will simply use our existing combi boiler which is not very old.

I will start threads in the relevant sections of the forum.

[JohnMo]

For UFH design you download loopcad for a 1 month free trial.  You build you house in the software and you can then experiment to get what suits you and the house.

 

If you are not air tight on the rest of the house MVHR, may not be the right way to go.  If you are, look on eBay for surplus stock clearance etc, my whole MVHR, cost £2700 for everything.  I went for oversized fan units to keep fan speed as low as possible, to ensure noise is as low as possible.  Match airflows in and out, in England I think it's 0.3 air changes per hour in Scotland 0.5.

[Olf]

1 hour ago, JohnMo said:

For UFH design you download loopcad for a 1 month free trial.

+1

Depending on the insulation of the structure, you may not need upstairs UFH at all - read through the forum, there is a specific thread on that.

 

1 hour ago, JohnMo said:

If you are not air tight on the rest of the house MVHR, may not be the right way to go

You should include airtightness strategy for the new build, which seems to be wrapping the original bungalow anyway. 

Even if a building is leaky, MVHR will still provide benefits: mostly by filtering incoming air and delivering/extracting at constant rates in targeted areas, just less of heat recovery element.

[iansr]

Thanks for the pointers guys.  The house is not going to be passive house level air tight but I think my builder can get it way better than a traditional construction. For example both front and back door apertures / doors will be new so there is an opportunity there to improve matters.

 

Re no UFH upstairs, do you mean have radiators instead, or nothing at all?  The existing external walls have cavity wall insulation and clearly the new walls will have good levels of insulation.  We will also be laying insulation in all the floors.

[Olf]

4 hours ago, iansr said:

do you mean have radiators instead, or nothing at all?

Towel rail in the bathroom, maybe some backup fan heater when Jack the Frost comes.

But it depends on whether you like bedroom warm or cold and how much heat escapes through the fabrics (via insulation and droughts losses). You mentioned new 1st floor and roof, so the latter is all up to you. In border cases the heat you generate may cause the upstairs to overheat, as documented here