How much heating do I really need to install in a well insulated house?

[miike]

My timber frame is going up in about 6 weeks time and I'm considering my options for heating the property. The house is 508m2 and I've been quoted £58 supply and install for UFH. An ASHP would be ~£10k installed, even with the £5k grant, for a house this size. This brings my total cost to fully heat the property at £40k. 

 

The timber frame has a U value of 0.15 - 0.09 and the windows (140m2 total) are triple glazed and U 0.6 - 0.8. So the property is going to be well insulated. 

 

I'm currently living in a new build apartment which has extensive double glazing and a B EPC rating (81 score). In the year I've lived here, I've turned the UFH on for 4 days when London was -8C and the internal temperature dropped to 17C. The heating has been off every other day and it is usually too hot in here and I'm trying to cool the place down. 

 

I would imagine my new house is going to similar, with keeping it cool due to the large amount of glazing being a bigger issue than keeping it warm. I'm connecting gas regardless as it was only £750 to do, so I can use that for hot water, but for heating the actual house I'm considering alternatives to UFH as I'm anticipating minimal demand. 

 

I see three options for me:

 

1. Suck up the cost and do full UFH throughout. Use either an ASHP or gas boiler to power it.

2. Partial UFH - instead of doing the full house, put it in the bedrooms, bathrooms and main living spaces. This would be about 250m2. 

3. No UFH - I can get a good price on german made infrared heaters and place them in most rooms in the house. I anticipate only occasional need to heat the property so they wouldn't be used very often and would cost ~£10k. 

 

There will be a MVHR system. If I could go with option 3, then it would enable enough funds to install air con in some of the rooms, which I feel would be a better use of the money. 

 

Curious to hear from people who have a highly insulated house and how often they actually need to use their heating. 

[Thorfun]

3 minutes ago, miike said:

The house is 508m2 and I've been quoted £58 supply and install for UFH

that's cheap! 😉 

 

4 minutes ago, miike said:

The timber frame has a U value of 0.15 - 0.09 and the windows (140m2 total) are triple glazed and U 0.6 - 0.8. So the property is going to be well insulated.

what is your expected airtightness score. All the insulation in the world won't do much good if the house is leaky.

 

once you have your airtightness score do a search on here for Jeremy's spreadsheet heatloss calculator and put in the figures. most folk on here have found it pretty accurate. that will give you an indication as to your heating requirements.

 

we installed our own UFH in our basement and our ground floor. total parts cost us about £2.5k. on the first floor we are having air conditioning as we're more likely to overheat than be cold but the AC will give supplementary heating if required. as we're not passive house we do expect to have some heating demand and I'm sure you will to. you also need to think about how you're going to heat your domestic hot water.

[miike]

6 minutes ago, Thorfun said:

that's cheap! 😉 

 

what is your expected airtightness score. All the insulation in the world won't do much good if the house is leaky.

 

once you have your airtightness score do a search on here for Jeremy's spreadsheet heatloss calculator and put in the figures. most folk on here have found it pretty accurate. that will give you an indication as to your heating requirements.

 

we installed our own UFH in our basement and our ground floor. total parts cost us about £2.5k. on the first floor we are having air conditioning as we're more likely to overheat than be cold but the AC will give supplementary heating if required. as we're not passive house we do expect to have some heating demand and I'm sure you will to. you also need to think about how you're going to heat your domestic hot water.

 

Thanks I'll take a look. 

 

What I've found in my current apartment is that the sun heats the place up through the glazing and the insulation then stops that heat leaving. So I would assume a similar situation in the new house but I'm not sure how you would factor the sun into heating requirements. 

 

Does your first floor gain much heat from the UFH on the floors below? I have a semi submerged basement and then two floors on top, so I could have UFH in the basement and rely on that to heat the upper floors as well. 

 

I can use a gas boiler for hot water. 

[ProDave]

Several people here including me took the "leap of faith" and only installed heating downstairs.  And it is true, in a well insulated house with good air tightnes and MVHR, you don't need any heating upstairs.  That will certainly cut down your install costs.

[Iceverge]

Hard to say without knowing airtightness levels. 

 

Form factor (external surface area Vs floor area) is  important too. 

 

Also glazing levels. Even the best windows normally only achieve a total u value of about 1.0 by the time you take into account thermal bridging due to install so even if they're the best windows they'll still be 6 times worse than your wall. If you have lots of windows......

 

 

HOWEVER. ......big houses have better airtightness scores and better form factor scores. Assuming you have MVHR I would think that 20w/m2 would be an adequate heat load for sizing the ASHP and 30w/m²/annum would cover the heating demand. 

 

So 508m2*20w ~ 10kW ASHP minimum. Add bit for DHW and mum maybe. 

 

Lets use gas first of all. 

And 508m2 X 30w/m2/annum ~ 15000kWh @10p/unit of gas =£1500 plus 1000kWh=£100 per person per year for DHW. With 5 occupants you would spend £2000.

 

OR 

 

ASHP @ a COP of 4 for heating all done on a TOU( time of use) tarrif at say 15p/KwH would be €562/year. DHW at a COP of 2.5 half day rate half E7 or similar would be ~£500. 

 

Total ~£1100 per year. 

 

Your mileage may vary depending on the cost of your utilities. 

 

In any case install UFH capable of using a low temperature input buried in the slab so you can bank heat on an ASHP using TOU at a later date if you go with gas initially. 

 

 

 

 

 

 

 

 

 

 

 

[TonyT]

With that size of property there must me some PV going on the roof!

 

coupled with ASHP/A2A it’s a no brainer

[JohnMo]

1 hour ago, miike said:

1. Suck up the cost and do full UFH throughout. Use either an ASHP or gas boiler to power it.

2. Partial UFH - instead of doing the full house, put it in the bedrooms, bathrooms and main living spaces. This would be about 250m2. 

3. No UFH - I can get a good price on german made infrared heaters and place them in most rooms in the house. I anticipate only occasional need to heat the property so they wouldn't be used very often and would cost ~£10k

1 no

2, main living space and wet rooms, bedrooms no, UFH in bedrooms is rubbish, you can't turn it off when you go to bed, it's heating all day when you don't need it. You may not need heating in bedrooms, if above a heated area.

3 IR heaters will be expensive to run - don't do it.

 

You need to get a different price for installing UFH. Or DIY.

 

We got our completion cert 4 months ago, original heating was gas, have since installed ASHP, mostly to make use of the cooling in summer. But even without E7 type tariff we think the ASHP will be cheaper to run than gas.

[SteamyTea]

16 hours ago, miike said:

My timber frame is going up in about 6 weeks time and I'm considering my options for heating the property

Did you not think about this at the design stage?

16 hours ago, miike said:

What I've found in my current apartment is that the sun heats the place up through the glazing and the insulation then stops that heat leaving. So I would assume a similar situation in the new house but I'm not sure how you would factor the sun into heating requirements

There is a lot to unpack here.

When you say 'apartment', do you mean a flat in a block?

The exposed areas, glass and walls, may be suck that you can easily collect several kWh of solar energy every day, but it cannot escape easily as it is walled in by other flats, that have the same problem.

 

We really do need to get away from over glazing and 'lots of natural light'. In is an energy use nightmare.

[JohnMo]

 

3 hours ago, SteamyTea said:

We really do need to get away from over glazing and 'lots of natural light'. In is an energy use nightmare.

You are correct

My glass wall leaks heat at a rate 7 to 8 time worse than the wall next to it. Yes they are triple glazed. Glazing alone accounts for over 1/3 of total heat loss.

 

We need to heat and cool because of it, good job I have solar and now a heat pump.

 

But we built the house for the views. Without those, I would not have bothered building.

 

 

[SteamyTea]

1 minute ago, JohnMo said:

But we built the house for the views. Without those, I would not have bothered building.

The views are set by your distance from the window, I get a good view of the telegraph pole outside.

[Conor]

19 hours ago, miike said:

 

Curious to hear from people who have a highly insulated house and how often they actually need to use their heating. 

 

Our 350m² house require about 40kWh of heat per day during he winter. That equates to 6hrs of the ashp running. UFH on all three floors, running as two zones (basement seperatly zone to rest of the house). UFH pipes in most rooms, at 200mm spacing. I wouldn't change the setup at all. 

 

With a 500m² house and a huge amount of glazing you'll need a substantial enough heat input, and cooling in the summer. Min 12kW ASHP. You'll need to do a detailed heat loss calculation. I reccomended getting somebody to put it through PHPP.

Edited July 12, 2023 by Conor

[JohnMo]

6 minutes ago, SteamyTea said:

The views are set by your distance from the window, I get a good view of the telegraph pole outside.

I get a good view of a loch and trees, from anywhere in the room.

[SuesieG]

Interesting to read all this as we are currently building - we are 360 sqm house ( 3 bed plus 2 bed granny annex - effectively a pair of semis with shared plant room and utility room). we will be the equivalent of passivhaus standard for insulation & air tightness with triple glazed windows - timber frame due aug 7th

We are having ASHP with wet  UFH downstairs. Also MVHR of course. we've had both SAP calcs done and Heat loss cals

We've lived with wet underfloor heating upstairs & down stairs for the last 30 years in our last self-build so fully understand how it works as well as MVHR. We will not be having ufh in bedrooms this time (response time is too slow & we like cold bedrooms overnight plus we are far more insulated & airtight)

so upstairs - debating which way to go :

1. bathrooms - wet underfloor heating & towel rail OR electric underfloor & towel rails

2. bedrooms - no heating - but putting in either electric points for future electric radiators if needed OR pipework ready for radiators if needed in future

We also have 12Kw solar pv with 17.4Kwh battery storage and 3 phase electric supply.

We too have large glazed south facing windows - for the stunning views (not a telegraph pole in sight!) but we have planned them with 1.5 meter overhangs & brise soleil to prevent overheating.

 

so electric or wet upstairs??

 

 

[JohnMo]

We are single storey and have wet UFH in bathrooms and electric towel rails. The combination works well for us.

 

Bedrooms we have ufh and it's rubbish. Been debating electric panel heater, but opening the doors works well enough to even the temperatures out. I would provision for a panel heater then wait for the first winter before buying anything to connect in.

 

We have big overhangs over our windows, but it's the westerly sun just goes under the overhang leading to overheating. So look at this aspect also.

 

 

[Conor]

55 minutes ago, SuesieG said:

Interesting to read all this as we are currently building - we are 360 sqm house ( 3 bed plus 2 bed granny annex - effectively a pair of semis with shared plant room and utility room). we will be the equivalent of passivhaus standard for insulation & air tightness with triple glazed windows - timber frame due aug 7th

We are having ASHP with wet  UFH downstairs. Also MVHR of course. we've had both SAP calcs done and Heat loss cals

We've lived with wet underfloor heating upstairs & down stairs for the last 30 years in our last self-build so fully understand how it works as well as MVHR. We will not be having ufh in bedrooms this time (response time is too slow & we like cold bedrooms overnight plus we are far more insulated & airtight)

so upstairs - debating which way to go :

1. bathrooms - wet underfloor heating & towel rail OR electric underfloor & towel rails

2. bedrooms - no heating - but putting in either electric points for future electric radiators if needed OR pipework ready for radiators if needed in future

We also have 12Kw solar pv with 17.4Kwh battery storage and 3 phase electric supply.

We too have large glazed south facing windows - for the stunning views (not a telegraph pole in sight!) but we have planned them with 1.5 meter overhangs & brise soleil to prevent overheating.

 

so electric or wet upstairs??

 

 

It costs very little to put an extra couple loops in to bathrooms. We have provision for electric towel rads but never bother wiring them up. The UFH works well. Put it in your bedrooms as well, again, very little cost, much else than having to buy panel heaters for all your rooms at a later date. We have one room where we didn't put UFH in and only part of the setup I regret. It's easy just to turn the flow down to individual rooms or off all together to get the temps right.

[TonyT]

1 hour ago, JohnMo said:

We are single storey and have wet UFH in bathrooms and electric towel rails. The combination works well for us.

 

Bedrooms we have ufh and it's rubbish. Been debating electric panel heater, but opening the doors works well enough to even the temperatures out. I would provision for a panel heater then wait for the first winter before buying anything to connect in.

 

We have big overhangs over our windows, but it's the westerly sun just goes under the overhang leading to overheating. So look at this aspect also.

 

 

 

I think that’s the best option, UFH on wet and towel rads electric, gives redundancy, ability to utilise as a dump load..

I use a smart socket)out with bathroom) and set a time schedule for mine to utilise cheap night time tariffs.

[Iceverge]

I wonder would wet UFH buried in the slab and a layer of electric underfloor heating just under the tiles for the summer be a worthwhile system just to de chill your feet. 

 

We don't have any heater in our bathroom but being in the bath with the air temp at 20deg can feel chilly when your skin is wet. 

 

I did put a cheapo fan heater in the shower room and it can get the room up to nearly 30 deg very quickly but it's a bit noisy. 

 

Maybe an IR heater just to warm your skin briefly when in the nip would be more pleasant. There doesn't seem to be any need to actually heat the room otherwise.

 

@Nickfromwales I'm sure will have chapter and verse. 

 

 

 

 

 

Edited July 12, 2023 by Iceverge

[Kelvin]

5 hours ago, JohnMo said:

I get a good view of a loch and trees, from anywhere in the room.

Exactly why we have a wall of glass too. The view is great. I’ll live with extra cost. 
 

The only heating we’ll have upstairs is an electric towel rail in the bathroom. I’ve wired for two panel heaters in the bedroom and dressing room and will wait for the first winter and see how we get on. 

Edited July 12, 2023 by Kelvin

[JohnMo]

1 hour ago, Iceverge said:

wonder would wet UFH buried in the slab and a layer of electric underfloor heating just under the tiles for the summer be a worthwhile system

Bath mat?

 

Our underfloor cooling runs in the bathrooms also. We just have a bath mat, Stepmom to when we get out of the shower.

[SteamyTea]

2 minutes ago, JohnMo said:

Stepmom to when we get out of the shower.

You what?

[JohnMo]

Spelling auto correct and me not reading, after I typed. Stepmom should read "step on"