Underfloor Heating ground and first floor and ASHP advice

[Gaz Bancroft]

Hi folks, 

 

I have planning consent and am just about to make building regs application. I am hoping for some opinion/advice on heating set up so that I can get this designed corectly from the start!  

 

The house is 144sq.m three-bedroom traditional construction. I am hoping to not bother with gas connection and go electric only with an ASHP. 

 

I would like to go for a wet underfloor heating to both ground floor and first floor. 

 

Queries:

1) Underfloor heating seems less common on first floor, why is that? Are there any particular difficulties that when I engage a builder/plumber they are going to take issue with? For ground floor the wet system will be integrated within the screed as is common practice, for first floor I've seen the first floor laid and then the system ducting clipped to the underside of the floor from underneath by snaking between the first floor joists with insulation then installed underneath the ducting to ensure the heat goes up into the bedrooms not down to the first floor. Looking for advice on the detail of the first floor construction make up as at this stage want to show on the building regs drawing and ensure is accommodated for from the outset. 

 

2) Presumably there would be no need to have any supplemental panel heaters and a good underfloor heating set-up will suffice? Would rather not have to have panel heaters as well as on a tight budget but if budget will allow I might spec electric towel rail in the bathroom and en-suite but not with super power output, simply for warming a towel if the room is already warmed.  

 

3) Thinking ahead I am planning on a decent quality vinyl floor covering throughout ground and first floor so not going to bother with carpets anywhere given the whole house will have underfloor heating. Is vinyl a good choice for underfloor heating?

 

4) As mentioned, I'm looking for ASHP and no gas. I'll have solar panels on the south facing pitch of the roof. Presumably an ASHP can heat both the underfloor heating and contribute to the heating of the DHW, but I appreciate that the DHW will then need to be supplemented with additional heating to get up to heat required for showers, hot water taps etc. What size ASHP is likely to be required? I'm thinking something like a 12kw? Obviously, I will take advice from a plumber/installer in due course but would be good to have an idea for my build cost spreadsheet! 

 

Many thanks in advance for any advice?

 

Gaz 

 

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Edited November 3, 2023 by Gaz Bancroft

[markc]

Good morning and welcome,

if the house is airtight you won’t need heating upstairs .. maybe a towel rail or two.

wet UFH downstairs is the way to go as long as you get the insulation and air tightness right. Are you looking at taking out the existing floors and putting in sufficient insulation to not loose heat through the floor?

just re read and I now think this is a new build? Not a renovation … much easier

Edited November 3, 2023 by markc

[Gaz Bancroft]

Hi Mark, 

 

Many thanks for the very swift response! Yeah its a new build so like I say just trying to design things right now at building regs and budgeting stage! 

 

New build so will be air tight but the location benefits from good outlook to the north elevation so I have designed French Doors off the lounge, dining room and master bedroom and with a dog running in and out these will get opened and heat inevitably escape! 

 

Whilst I am on a tight budget it feels like a missed opportunity to do away with heating entirely upstairs. I was thinking underfloor heating upstairs or the alternative being electric panel heaters that can just give bedrooms a quick blast of heat before bed or in a morning if required. But I don't want to pay for both! 

[HughF]

‘New build, so will be airtight’…. You sure about that?

[joe90]

Despite being on a tight budget, insulate, insulate, insulate, you only pay fir it once. Air tightness will completely rely on good workmanship and an eye to detail, dont assume a new build will do this. I installed an ASHP with wet UFH downstairs and I had no heating upstairs in my build apart from towel rads in bathrooms and electric UFH in the en-suite. Very occasionally (feeling unwell, very cold spell) I planned to use plug in fan heaters/panel heaters, shame to pay for heating that only gets used a couple of times a year?

[ProDave]

Fit MORE insulation under the ground floor slab, a lot more.  300mm is probably a good target to aim for. And wider cavity with more insulation in them.  You build a house once and get one chance to do it right.  You will never get the chance to improve it later and will probably regret not doing it right.

 

You are aiming to get the heat input down as low as possible.  UFH should then work fine.  If you do it really well like many of us have the house ends up so well insulated you don't need any heating at all upstairs, but fit upstairs UFH unless you are really certain of that and really determined to detail it properly.  Do it properly and many of us are heating a house that size with a 5kW ASHP.

 

If you are doing this properly, you get a Design SAP done which will tell you all that.  It is a requirement for building regs in Scotland, but so few people seem to get it done down south that I suspect it is optional?

 

It is not so much the design on paper that lets a building down, but unless you are detailing everything yourself, or have a really trusted contractor who actually understands low energy houses, then a typical house gets let down by poor details, e.g badly fitted insulation so cold air can bypass some of the insulation, and poor details at junctions.  If you are having a cold loft then the details of how to insulate and air tight seal the upstairs ceiling is one of the major details that is often done poorly.

 

And I know you are only asking about heating, but don't block your downstairs hallway.  You WILL get fed up having to go through the kitchem / diner to get to the back.  Scrap those cupboards and have a hall you can walk through front to back.

[JohnMo]

1 hour ago, Gaz Bancroft said:

would like to go for a wet underfloor heating to both ground floor and first floor. 

Ground floor yes, in bedrooms not the best to slow to respond. So never really the right temp when you get up or go to bed. In wet rooms it's good, but add an electric towel rad also.

 

1 hour ago, Gaz Bancroft said:

4) As mentioned, I'm looking for ASHP and no gas. I'll have solar panels on the south facing pitch of the roof. Presumably an ASHP can heat both the underfloor heating and contribute to the heating of the DHW, but I appreciate that the DHW will then need to be supplemented with additional heating to get up to heat required for showers, hot water taps etc. What size ASHP is likely to be required? I'm thinking something like a 12kw? Obviously, I will take advice from a plumber/installer in due course but would be good to have an idea for my build cost spreadsheet

Solar - thermal or PV?

 

ASHP can do UFH and all DHW. No additional heating required, but if there is the cylinder will have an immersion.

 

12kW why that big, do your heat loss calculations then select the size. To big makes life difficult, cost more need more equipment to keep it happy.

 

 

[Conor]

Ashp fine for getting hot water. We've ours set to 45c and don't need it any hotter. You just need a big enough tank. Also great piece of mind with young kids in the house and no risk of scalding.

 

A couple towel rads on the top floor run by the ashp will do the job - no need to any direct electric heating anywhere.

 

We put UFH in anyway as we've concrete beam floors and screed... No brainer to put the UFH as costs were minimal. Three towel rads still sitting in their boxes!

 

As others have said, get a detailed heatloss analysis done and take it from there. You'll end up looking at a 5-9kW heatpump. We're 315m², three story and out 9kW heatpump does the job well. No way you'll need a 12kW.

[Gaz Bancroft]

Hi all, 

 

Many thanks for the advice, this has been really helpful. 

 

On 03/11/2023 at 02:15, JohnMo said:

Solar - thermal or PV?

PV

 

So, I think what I am going to go for is underfloor heating to ground floor and electric panel radiators upstairs including electric towel rails in bathroom and en-suite. I think on balance this is probably the most cost effective for me both in terms of install and running costs. I'm hoping the upstairs panel radiators won't get much use but are there for cold snaps when the bedrooms might need a blast of heat before bed. 

 

Noted about air tightness and insulation being key. So, at the moment spec is;

FLOOR. U Value of 0.12W/m²K. (150mm thk Ecotherm Eco-Versal )

WALLS. U Value of 0.18W/m²K. (90mm thk Ecotherm Eco- Cavity Full Fill)

CEILINGS. U Value of 0.11W/m²K. 400mm Earthwool

WINDOWS/FRENCH DOORS/FRONT DOOR. To have a U Value of 1.20W/m²K, or better. 

 

On 03/11/2023 at 02:06, ProDave said:

Fit MORE insulation under the ground floor slab, a lot more.  300mm is probably a good target to aim for

I will speak to architect about increasing floor insulation to 300mm. 

 

Also going to speak to window manufactures and consider if go triple glaze if can get the U Value for the windows down given I have a lot of glass in the north facing elevation. 

 

Thanks again for the input 

 

[Conor]

If I were to pull any weak points from that list it would be the walls and windows. I'm not sure if 90mm insualtion gives you 0.18 anyway unless you've something else going on. Aim for 0.15. And for windows, definitely triple. Ours average at 0.8, some are 0.5 (a 40mm thick, 2x2.4m unit), and not that expensive in overall scheme of things. About the same as kitchen and bathrooms combined.

[HughF]

Yeah that’s a pretty lousy spec for a new build…. We did a simple rear extension this summer, ended up 150 full fill cavity and 0.98 triple glazed fenestration products. 200mm pir in the floor.

 

Emptied a couple of rolls of air tightness tape round the windows and cavity closers, used Compriband and fm330 around the windows.

Edited November 6, 2023 by HughF

[Iceverge]

9 hours ago, Gaz Bancroft said:

the moment spec is;

FLOOR. U Value of 0.12W/m²K. (150mm thk Ecotherm Eco-Versal )

WALLS. U Value of 0.18W/m²K. (90mm thk Ecotherm Eco- Cavity Full Fill)

CEILINGS. U Value of 0.11W/m²K. 400mm Earthwool

WINDOWS/FRENCH DOORS/FRONT DOOR. To have a U Value of 1.20W/m²K, or better. 

 

I'm thinking ecotherm did the U value calcs and passed them onto your designer. 

 

They are hallucinations unfortunately. 

 

Start at 200mm PIR (or 300mm EPS)in the floor. 200mm mineral wool in a full fill cavity and 3g good quality UPVC windows and doors. Avoid french doors and brush sealed sliders. They leak like the Titanic. Instead make sure all doors and windows have compression seals to shut.