Selfbuild heating choice

[GreenT]

Hello,

We are about to start on a self build project, but have been going round and round trying to decide on heating. The house will not be passive, but not too far off. High levels of insulation, triple glazed, MVHR etc.  We are not going to use gas, so we need to decide between an ASHP with UFH or infra red panels. We also want PV. Our builder thinks the heat demand will be so low, that investing in an ASHP would be a waste of money as the PV would take care of hot water in the summer, so the ASHP would only be used a few months of the year. I’ve been trying to research whole house infrared heating, but it appears to be a polar issue. Any advice welcome

[Declan52]

Have you got your sap figures worked out so you have a better understanding of what your heat demand will be. After that it will be more how you intend to live in the house i.e will there be 5/6 people trying to get showered each morning. 

[GreenT]

Thanks for your reply Declan,

 

I haven’t got the SAP info to hand, but I understand we could get SAP approval using electricity as the only heat source. We are a family of 4 and don’t like to run a warm house, but it feels like a big risk not putting UFH in and relaying on Infrared. Is anyone out there using infrared as the only heat source in a new build?

[ProDave]

I think we discussed IR panels and nobody could find a good reason for them.  They seem more aimed at heating the occupants (not the building) of poorly insulated occasionally used buildings.  e.g out local church uses IR heaters hung from the ceiling to warm the congregation rather than try and keep a poorly insulated old building warm.

 

In a hear passive house all they would so is warm up the fabric of the house in exactly the same way as any other heat source at exactly the same energy usage.

 

We use an ASHP and it works fine for space and water heating.  We don't get all of our DHW from PV. though that nice spell in late April / early May we came very close to 100% PV water heating.

 

[Mr Punter]

I thought IR heating was restricted to outdoor smoking areas, manned warehousing etc.

[AliG]

Working off 100l per person per day of hot water, your requirement for hot water heating will be 20kWh a day. I think your builder is optimistic, there are plenty of cloudy days in summer as well as sunny days when you will generate more hot water than you can use and there is no guarantee that the generation of PV coincides with the need for hot water, although this can be managed with a larger tank. PV will only cover your DHW for a few months of the year. Also PV is better used to offset normal electricity use which is more expensive than using an ASHP to heat water.

 

When you don't have any PV or run out of hot water, heating it with direct electricity will be quite expensive. Around £2.50 a day, versus less than £1 for an ASHP. So you would probably save around £300 a year on DHW using an ASHP, offset by the higher cost of the ASHP.

 

If the house is close to passive but not passive the favoured system seems to be UFH on just the ground floor with an ASHP. As soon as you use direct electricity for heating the costs will rise above my calculation for hot water and eventually the ASHP would pay for itself as well as having a more comfortable house when it is cold.

[GreenT]

Thanks for your replies guys, I think I agree that ASHP is the way to go. Only another 2000 decisions to go ?

[Dan F]

1 minute ago, GreenT said:

Thanks for your replies guys, I think I agree that ASHP is the way to go. Only another 2000 decisions to go ?

 

You'll need to give ASHP size some thought as you'll probably need quite a small one for heating, but DHW might require a larger one.  What are you doing for DHW storage?

 

Also, another reason to use ASHP is potential for cooling in the summer which works well with passive slab type foundations.

[nod]

1 hour ago, GreenT said:

Hello,

We are about to start on a self build project, but have been going round and round trying to decide on heating. The house will not be passive, but not too far off. High levels of insulation, triple glazed, MVHR etc.  We are not going to use gas, so we need to decide between an ASHP with UFH or infra red panels. We also want PV. Our builder thinks the heat demand will be so low, that investing in an ASHP would be a waste of money as the PV would take care of hot water in the summer, so the ASHP would only be used a few months of the year. I’ve been trying to research whole house infrared heating, but it appears to be a polar issue. Any advice welcome

I agree with your builder While we have no MVRH We have gas fuels UFH and lots of insulation 

Radiators for the first floor have never been used  The UFH only kicks in on the coldest days 

[scottishjohn]

3 hours ago, GreenT said:

but it feels like a big risk not putting UFH in and relying on Infrared.

If using insulated slab founds  as per Passiv house ,,then extra cost to throw UFH piping in slab is very small at build stage 

even if you never connect it .

but then If you have access to mains gas -your choice is even wider 

a small gas boiler will be cheaper than an ASHP and i think it is still cheaper to run +gives option of gas cooking which some prefer

If no mains gas --then definately ASHP

[Conor]

Another thing to think about is resale... I've been advised by more than one estate agent that if you have an "eco house" with no central heating, it will be worth less than a conventional house and be more difficult to sell. UFH is pretty much expected in a good quality house in most markets. 

 

We're very similar, house will be built to passive standards, just putting in UFH in the ground floor and a 5kw ASHP. Nothing upstairs, maybe electric towel rads in the bathrooms. Running your ASHP for heating and hot water in the early hours during off peak rates will cut the costs even more.

[Gone West]

5 hours ago, GreenT said:

We are a family of 4 and don’t like to run a warm house

We have build to better than PH standards, U = 0.09 air tightness = 0.47 and don't have UFH and heat the house to 23C with towel rails as the main source of heating. If you are happy with 20C or less then it would be easy to heat without UFH depending on where you are in the country. There might be a problem convincing a buyer if you wish to sell the house though. We wouldn't be happy with a cool house.

[SteamyTea]

@PeterStarck

What U-Value is your floor.

That makes a difference to the losses from UFH.

Also the overall size of the building is important. Area to volume ratios make a difference, ask anyone with a small house.

[Gone West]

1 hour ago, SteamyTea said:

@PeterStarck

What U-Value is your floor.

That makes a difference to the losses from UFH.

Also the overall size of the building is important. Area to volume ratios make a difference, ask anyone with a small house.

The overall U value is 0.10

[SteamyTea]

40 minutes ago, PeterStarck said:

The overall U value is 0.10

So very little floor losses then.