UFH or not ?

[Nic]

My build is about to start next month down in Devon . Having timber frame and passive principles ( still waiting on SAP but u value all round is about 0.10 walls/ roof etc and triple glazed windows/doors ). But not decided if I even need to go with UFH , which would clearly need to go onto the insulation and under the screed ? Or pop some electric mats down  or those new uv mats ( just in case ?) 
 

what is the general thoughts here ? 

[joth]

Wet UFH everytime

 

 

Worst case is you don't need it, but it's relatively cheap to install the pipes anyway during build vs virtually impossible to add them when you find out you should have done later. This logic holds regardless of sap, phpp etc. 

 

[JohnMo]

If you have choice of finding spaces for radiators or everything hidden, I would go everything hidden. Plus lower flow temperature for better efficiency.

 

Wet UFH everywhere, plus you could add electric (in addition) in ensuite and bathroom, if you want if hot underfoot, and for off season heating. Add electric towel rads for bathrooms either way.

 

You don't need much piping in the floor for UFH to work (if well insulated), we are on a loose 300mm pipe centre and it works fine 

[SteamyTea]

Have you thermally modelled your new build.

If not, now is the time to do it.

You need to do a room by room analysis, not just an overall loss calculation.

 

Also remember that, via conduction, thermal energy can travel downwards/sideways though the floor, so you need bare that in mind.

[Nic]

6 hours ago, JohnMo said:

If you have choice of finding spaces for radiators or everything hidden, I would go everything hidden. Plus lower flow temperature for better efficiency.

 

Wet UFH everywhere, plus you could add electric (in addition) in ensuite and bathroom, if you want if hot underfoot, and for off season heating. Add electric towel rads for bathrooms either way.

 

You don't need much piping in the floor for UFH to work (if well insulated), we are on a loose 300mm pipe centre and it works fine 

 

thanks , and is there any type of wet UFH that is better when in screed ? 

[JohnMo]

13 minutes ago, Nic said:

 

thanks , and is there any type of wet UFH that is better when in screed ? 

Not as far as I am aware. Clip the pipes to the insulation - screed, done.

[Iceverge]

Been there, got the no UFH T shirt. We didn't do it because our plumbers wanted an arm and a leg and I was stubbornly of the opinion that passive houses don't need heating. (Untrue, they only need very little heating)

 

If it isn't scandalously expensive, stick in few loops of UFH to allow you to heat the house like @TerryE by banking cheap tariff electricity. 

 

Passive class houses are like those old Soviet jets, they'll run on anything. A couple of fan heaters, a stove, A2AHP, a brace of energetic children/dogs  , whatever will heat the house. Don't over complicate it with zones etc. UFH mats under the tiles for the bathrooms too.

 

 

[Nickfromwales]

8 hours ago, SteamyTea said:

You need to do a room by room analysis, not just an overall loss calculation.

I've stopped doing room by room, you just end up chasing your M&E tail tbh. Most rooms achieve an ambient, regardless, and rooms with lower temps attract heat from adjoining spaces, so seems a more pragmatic approach in most instances to just copy/paste/calculate.

[Nickfromwales]

2 hours ago, Nic said:

 

thanks , and is there any type of wet UFH that is better when in screed ? 

Not really, and I've been installing for 30+ years. Just look at getting more pipe in than you will be recommended by the "knee-jerk" posse, and install at 100mm centres on an 'inverted loop' pattern. This will promote better W/m2 with the lowest possible flow temps. This takes heated water to the centre of the room quicker, vs 'serpentine'.

Insulation will be the biggest issue, and the more you put in, the less heat the floor will require to do the same job. 

[Nickfromwales]

Get your insulation from https://www.secondsandco.co.uk/ and please send me 10% of whatever you save so I can buy beer for the needy (myself). It's a genuine cause, I assure you.....ahem.....

[SteamyTea]

25 minutes ago, Nickfromwales said:

I've stopped doing room by room, you just end up chasing your M&E tail tbh

So how do you size the thermal emitters?

And take into account differing window sizes.

[Nickfromwales]

6 minutes ago, SteamyTea said:

So how do you size the thermal emitters?

And take into account differing window sizes.

Do the rooms, spaces etc, add it altogether, and utilise the average. Then look at the dwelling fabric / solar gain, and so on, and include any other known peripherals to the mix.

Rooms and spaces are simply boxes within a defined global "heated and (sometimes) airtight envelope", and IMHO what happens within that divisible space is very difficult/near impossible to differentiate.

[SteamyTea]

2 minutes ago, Nickfromwales said:

defined global

Which is inside a semi infinite heat sink.

 

Sounds like you actually do a room by room calculation, but then fudge it at the end.

[Nickfromwales]

5 minutes ago, SteamyTea said:

Which is inside a semi infinite heat sink.

 

Sounds like you actually do a room by room calculation, but then fudge it at the end.

Overall heat loss primarily, and then part O ( and common sense before it ) for overheat. TBF, it varies very differently house to house, with a live survey and some grey matter applied accordingly, and then you can get a proper handle on which 'ends/sides' of the house will need some better thought and strategizing.

I dislike fudge, as installed systems are expensive to amend retrospectively. Not had to do that, yet, 🤞

[Iceverge]

2 hours ago, SteamyTea said:

So how do you size the thermal emitters?

And take into account differing window sizes.

 

Get you fabric right and anything/anywhere will heat the house. 

 

My Mrs just flicked the switch on that 900w thermostatic electric rad. It will tick over from now until morning on cheap leccy. The whole place stays at about 20-21 Deg. 

 

 

It makes little difference where you put the rad downstairs.

 

I'm waiting on my heat pump mate to do the gas connection on the A2A in the hallway. That's only going in  to save €500/annum on electricity though.

 

Otherwise I really appreciate the simplicity of direct electric. 

Edited October 23 by Iceverge

[joth]

On 23/10/2024 at 21:23, Nickfromwales said:

Overall heat loss primarily, and then part O ( and common sense before it ) for overheat. TBF, it varies very differently house to house, with a live survey and some grey matter applied accordingly, and then you can get a proper handle on which 'ends/sides' of the house will need some better thought and strategizing.

I dislike fudge, as installed systems are expensive to amend retrospectively. Not had to do that, yet, 🤞

 

My experience for passivhaus (N=4 now) is

1/ never plan for "no heating" - seen this in one, the regret (and cost and disruption) of not laying UFH pipes is real. (I advised they should but by the time I was formally employed, the floor was already poured)

2/ a building wide model (e.g. PHPP) is just fine for heating - so long as the heat emitters are sensibly distributed through the area

3/ room by room is more necessary for cooling requirements than heating requirements - especially bedrooms 

 

[TerryE]

On 23/10/2024 at 21:17, SteamyTea said:

Which is inside a semi infinite heat sink.

 

Sounds like you actually do a room by room calculation, but then fudge it at the end.

 

If the ext walls, floor, roof do genuinely have a U-value of 0.1 then that is pretty much an order of magnitude better then interior wall so treating floors as a single zone and ignoring interior walls is a good simplification.  

 

Don't forget airtightness and go for 0.5 ACH + MVHR.  so no weep vents.  

 

I circulate my UFH loops for 15 min every 3 hours so I can use the manifold return temp to take the average slab temp and this also spreads any solar gain across the whole slab.

[G and J]

On 25/10/2024 at 10:05, TerryE said:

 

I circulate my UFH loops for 15 min every 3 hours so I can use the manifold return temp to take the average slab temp and this also spreads any solar gain across the whole slab.

How do you make that happen?   It sounds like a really good idea.

[JohnMo]

50 minutes ago, G and J said:

How do you make that happen?   It sounds like a really good idea.

I currently let my ASHP circulation pump run all the time, it takes heat from the house and via a fan coil keeps our summer house warm all year. Even taking 21/22 Deg floor temp it seems to keep the summer house above 18/19. Plus any solar gains get balanced out.

[G and J]

39 minutes ago, JohnMo said:

I currently let my ASHP circulation pump run all the time, it takes heat from the house and via a fan coil keeps our summer house warm all year. Even taking 21/22 Deg floor temp it seems to keep the summer house above 18/19. Plus any solar gains get balanced out.

And I like that idea, but I want to keep the automation to v simple, off the shelf bits of kit only.  

[JohnMo]

2 hours ago, G and J said:

And I like that idea, but I want to keep the automation to v simple, off the shelf bits of kit only.  

Mine couldn't be more easy, its the default setting on the ASHP when doing WC. When compressor is off it just drops to 12L/min.

[G and J]

1 hour ago, JohnMo said:

Mine couldn't be more easy, its the default setting on the ASHP when doing WC. When compressor is off it just drops to 12L/min.

I like that level of complexity.   I’ll have one of those please!

[Kelvin]

I’ve finally got around to installing my Hi-Fi amp and AVC surround sound amp. Both are very meaty amps so get hot when running. The Musical Fidelity amp runs hot all the time and Denon AVC amp really only gets hot when pushed. The TV also gets hot plus there are several other devices in the rack all generating a little bit of heat. It’s more than enough to heat the TV room which is 4m x 5m. Opening the doors and it will add a little bit of heat to the rest of the house. Add in two people and two dogs and it’ll be unusable in the summer. 😂 

Edited October 27 by Kelvin

[JohnMo]

29 minutes ago, Kelvin said:

I’ve finally got around to installing my Hi-Fi amp and AVC surround sound amp. Both are very meaty amps so get hot when running. The Musical Fidelity amp runs hot all the time and Denon AVC amp really only gets hot when pushed. The TV also gets hot plus there are several other devices in the rack all generating a little bit of heat. It’s more than enough to heat the TV room which is 4m x 5m. Opening the doors and it will add a little bit of heat to the rest of the house. Add in two people and two dogs and it’ll be unusable in the summer. 😂 

Sounds like you have some expensive panel heaters disguised as a TV and amplifiers.

 

Just check our TV it's been on for the last hour and it's almost cold to touch.

[Kelvin]

The TV has a FALD backlight screen (full array local dimming) which tends to get warm.  The Musical Fidelity amp has a large heat sink on either side of the case and they get very hot, almost too hot to touch.