Passive build - electric heating?

[Mayobuild]

We are building a timber frame house and a naturally warm people, everyone we talk to says we’ll be roasted and any new house we’ve been in we’ve commented on how we would manage with the heat.

We have the option to go passive with the timber frame, theres a difference of €6k between the standard package (U value 0.18) and the passive at 0.13 U value.

 

Would it be an option to go with the passive and go for electric heaters. Greater control over the running of the heating and if it is as warm as people say they won’t be used as much. Electric underfloor element for the bathrooms. We’ll have a solar PV installed, adding batteries could help manage the load better.

 

Is this a viable option or has anyone done anything similar?

 

As a follow on, what would be the best way to solve our hot water demand?

 

Thanks

[ProDave]

Depends where you are and your climate (you price in € as the only clue to your location)

 

Under floor heating from an Air Source Heat Pump will be the cheapest "electric" heating.  Roughly 1/3 the cost of direct electric heating.  And it can heat your hot water as well.

[Kelvin]

Overheating is often a bigger problem than heating such a house. What’s the rest of the design like? (Lots of glass etc) 

[Gone West]

1 hour ago, Mayobuild said:

We are building a timber frame house and a naturally warm people, everyone we talk to says we’ll be roasted and any new house we’ve been in we’ve commented on how we would manage with the heat.

We have the option to go passive with the timber frame, theres a difference of €6k between the standard package (U value 0.18) and the passive at 0.13 U value.

Our timber frame worked out at 0.095 U value and we heated the house with just three electric towel rails and warm air from a 685W EASP. We kept the whole house at 23C.

[joe90]

£6k is a small percentage of a build cost. As @ProDave says, ASHP is the cheapest way of electric heating, will do DHW, and (some) can so cooling to cope with overheating and solar will run this during sunny weather.

[SteamyTea]

Welcome.

 

Depending on the layout, air to air heat pumps (A2AHP) may be a cost effective option. You will still need to find a way to heat your domestic hot water (DHW), but there are several options there.

 

The U-Values toy have been quoted are nothing special, but it does depend on the wall area.

 

If you go for underfloor heating, the amount of insulation under it becomes important as you have a greater temperature difference (∆T).

 

The smaller the house heat load is, the small the problem of heating it is.

[JohnMo]

1 hour ago, Mayobuild said:

passive at 0.13 U value.

 

You really need to complete a heat loss calculations, we have 0.14 walls, 0.09 floor and between 0.11 and 0.14 roof, and pretty airtight - we defiantly need heating in NE Scotland.  Your form factor makes a huge difference to heat load, ours is rubbish (long thin building and all vaulted ceilings), but suits the location and views.

 

No matter what you decide, put UFH pipes in all down stairs rooms. We put ours in a 300mm centres - very small cost and nothing lost.  You could connect to a heat pump or heat on a cheap rate via a Willis heater or two. 

[MikeSharp01]

1 hour ago, JohnMo said:

Willis heater or two

Willis heaters are like immersion heaters for flowing water so you just put them in the UFH circuit and away you go.

[LeenToo]

@Mayobuild interested to know what you went with for a finish. I am in the same boat, don't want to fork out big bucks for a heat pump that may get very little use.........

[Nickfromwales]

6 minutes ago, LeenToo said:

@Mayobuild interested to know what you went with for a finish. I am in the same boat, don't want to fork out big bucks for a heat pump that may get very little use.........

What is your strategy for meeting part O and getting some active cooling? If you don’t or won’t need the heat then you’ll be well insulated and airtight, yes? 
 

<£3k for a good Panasonic monoblock, 5/7kW capacity, and capable of cooling straight out of the box.

 

You’ll need hot water year round, so the perceived savings on heating may be skewed by producing DHW via direct electricity.

 

Solar PV will sort DHW out for a lot of the summer, or batch heating it at night with a bigger cylinder on ultra cheap rate electricity.

 

Summer overheating is the biggest enemy, don’t underestimate this.  

[JohnMo]

10 minutes ago, LeenToo said:

@Mayobuild interested to know what you went with for a finish. I am in the same boat, don't want to fork out big bucks for a heat pump that may get very little use.........

Way to many variables. What is your heat demand? If it's 2kW at -3 it will.be about 1kW at 7 degs. A heat pump will give you a SCoP of 4 or a quarter the running cost of direct electric. Plus a sunny winter day make the most of any excess PV. A 7 Deg day CoP of 5 + at -3 CoP of 3.

[LeenToo]

4 hours ago, Nickfromwales said:

What is your strategy for meeting part O and getting some active cooling? If you don’t or won’t need the heat then you’ll be well insulated and airtight, yes? 
 

<£3k for a good Panasonic monoblock, 5/7kW capacity, and capable of cooling straight out of the box.

 

You’ll need hot water year round, so the perceived savings on heating may be skewed by producing DHW via direct electricity.

 

Solar PV will sort DHW out for a lot of the summer, or batch heating it at night with a bigger cylinder on ultra cheap rate electricity.

 

Summer overheating is the biggest enemy, don’t underestimate this.  

Not sure what part O is or whether we have that in Ireland?

 

Hoping to build to Enerphit standard so well insulated and airtight yes. I was thinking AC alright but my architect kind of put me off with stories about someone who tried it and wasn't happy. 

 

We have a canopy planned to shade southern windows so hopefully this will offset overheating to some degree and ye we will use solar pv and night rate to heat water. Have you seen anyone using AC for this kind of build and were they happy with it. I have been thinking about electric radiators in lieu of AC.

Thanks for the response Jason

[LeenToo]

4 hours ago, JohnMo said:

Way to many variables. What is your heat demand? If it's 2kW at -3 it will.be about 1kW at 7 degs. A heat pump will give you a SCoP of 4 or a quarter the running cost of direct electric. Plus a sunny winter day make the most of any excess PV. A 7 Deg day CoP of 5 + at -3 CoP of 3.

Yes thanks for that John but way over my head. I don't know what the heat demand will be as we only just have planning and are looking at the specs for timber frame etc currently

[JohnMo]

13 minutes ago, LeenToo said:

Enerphit standard

Isn't really a new build standard so is quite easy to achieve.

 

It has a heating requirement of 25W/m². So a 200m² house would have a max heating demand of 5kW on your coldest day - so worst case. So over a 24 hrs period is 120kWh of heat needed. So the coldest day would cost (at 25p per kWh) £30. With a heat pump or A2A £10. A more average heating day would used half the heat energy, so direct electric heating (£15). With heap pump nearer £6, due to better CoP.

 

CoP, is coefficient of performance, so electric input compared to heat output. CoP of 5 is 1kWh electric and 5kWh heat out.

 

 

 

[SteamyTea]

Irish Building Regulations are here.

https://www.gov.ie/en/collection/d9729-technical-guidance-documents/

 

Quick search it seems that Irish Part L covers overheating.

[LeenToo]

42 minutes ago, JohnMo said:

Isn't really a new build standard so is quite easy to achieve.

 

It has a heating requirement of 25W/m². So a 200m² house would have a max heating demand of 5kW on your coldest day - so worst case. So over a 24 hrs period is 120kWh of heat needed. So the coldest day would cost (at 25p per kWh) £30. With a heat pump or A2A £10. A more average heating day would used half the heat energy, so direct electric heating (£15). With heap pump nearer £6, due to better CoP.

 

CoP, is coefficient of performance, so electric input compared to heat output. CoP of 5 is 1kWh electric and 5kWh heat out.

 

 

 

Thanks John its only 130 sq m so that's not too bad based on your calculations. My reservation is spending big on a heat pump that I am thinking I may not use too much. I don't like electric radiators per se but if they don't cost much to install and I am not using them much to heat the house this seems like a good compromise. I will definitely have a good solar PV system and decent battery so some of the electricity will be home grown.

[JohnMo]

3 minutes ago, LeenToo said:

spending big on a heat pump

Look on eBay, I paid £1300 delivered. There a good ones on there currently for £1000.

 

You need a cylinder a heat pump cylinder is only a couple of hundred more than a direct immersion one.

 

UFH throughout, run direct from heat pump, you have heat and cool for very little cost. All you need is pipes and manifold run direct from HP.

[SteamyTea]

17 minutes ago, LeenToo said:

only 130 sq

 

10 minutes ago, JohnMo said:

UFH throughout

Have to factor in extra floor insulation.

[Iceverge]

In Ireland here too. 

 

Didn't install any heating whatsoever at the beginning. Designed and built to passive house standards. 

 

Actual measured heat demand was 17kWh/m2 over 186m². (3200kWh/annum)

 

We just used a free plug in radiator. So long as you ran it for long enough it was fine. If it was anywhere downstairs it didn't make much difference, the house was warm. 

 

However I had hoped to do all the heating on the night rate which was then 8c/kWh. At my estimated €250/annum an ASHP would never have paid back before it broke or wore out. 

 

However in reality we did need to turn the radiator on earlier as the house wouldn't be warm enough by 6pm-midnight otherwise. This took half our usage outside the night rate electric and with the electricity price increases our annual heating bill was about €750. 

 

I bought a new Daikin A2A unit from eBay Italy for €1100. (Post Brexit everything UK sourced has Vat and Customs duty) It's running at a COP of about 3.3 so our annual bill for heating is back down to €230. It'll pay itself back in 3 years including install costs.

 

Our actual measured DHW demand is about 3500kWh per year for 2 adults and 3 small kids. With a direct 300l cylinder it all gets done on night rate and costs €440/annum. We have no solar yet. 

 

I also installed €50 pull cord heaters in the bathrooms for extra comfort post shower. These work well. I think on balance the fan type is better than the infrared type but it's a little noisy on a stud wall. 

 

If I was to do it all again.........

 

If I could find a way to get a 5kW ASHP with UFH installed for about €5k I think I'd do that. 

 

Otherwise a central placed A2A €1500, 3X fan heaters €150 and a direct UVC €1000 and spend the other €2.5k left over on solar PV would be cheaper in the long run. 

 

 

 

 

Edited February 27 by Iceverge

[Iceverge]

TLDR. 

 

Passive house. Initial use of electric only was dearer than expected so installed an A2AHP. This is proving economical. 

[LeenToo]

38 minutes ago, Iceverge said:

In Ireland here too. 

 

Didn't install any heating whatsoever at the beginning. Designed and built to passive house standards. 

 

Actual measured heat demand was 17kWh/m2 over 186m². (3200kWh/annum)

 

We just used a free plug in radiator. So long as you ran it for long enough it was fine. If it was anywhere downstairs it didn't make much difference, the house was warm. 

 

However I had hoped to do all the heating on the night rate which was then 8c/kWh. At my estimated €250/annum an ASHP would never have paid back before it broke or wore out. 

 

However in reality we did need to turn the radiator on earlier as the house wouldn't be warm enough by 6pm-midnight otherwise. This took half our usage outside the night rate electric and with the electricity price increases our annual heating bill was about €750. 

 

I bought a new Daikin A2A unit from eBay Italy for €1100. (Post Brexit everything UK sourced has Vat and Customs duty) It's running at a COP of about 3.3 so our annual bill for heating is back down to €230. It'll pay itself back in 3 years including install costs.

 

Our actual measured DHW demand is about 3500kWh per year for 2 adults and 3 small kids. With a direct 300l cylinder it all gets done on night rate and costs €440/annum. We have no solar yet. 

 

I also installed €50 pull cord heaters in the bathrooms for extra comfort post shower. These work well. I think on balance the fan type is better than the infrared type but it's a little noisy on a stud wall. 

 

If I was to do it all again.........

 

If I could find a way to get a 5kW ASHP with UFH installed for about €5k I think I'd do that. 

 

Otherwise a central placed A2A €1500, 3X fan heaters €150 and a direct UVC €1000 and spend the other €2.5k left over on solar PV would be cheaper in the long run. 

 

 

 

 

My architect was telling me a story of someone who had installed A2A and it didn't work properly or he didn't like it and he was very unhappy. I am not sure i would like UFH having lived in a house with solid fuel and cold/cool floors all my life.

Wonder about what it is like having hot air blowing around a room but reckon that a passive house would probably heat up very quickly so A2A would only be on sporadically. 

Also modern tastes seems to be for houses to be 19-21 degrees C whereas I am happy with less and uncomfortable with more, that comes from living in some very old droughty damp houses in the west of ireland over the years. Interested in how you find the A2A and do you use for cooling also. Thanks!

[Iceverge]

There is some absolute crap out there so be careful what you believe and as usual the devil is in the detail. Corner your architect and find out the exact model number, the installed house heat demand and the usage patterns. Without these their info is more akin to hearsay than professional advice. 

 

The A2A is probably even more dependant on getting the right model than an A2W HP as there is tens of thousands of models and most of them are focused on cooling. The wrong model will ice up very quickly in heating mode. 

We got a Daikin FTXM25R after a lot of research. It makes noise. Probably as much as a desk fan. I wouldn't want it over my bed head but it's fine in the hall.  The only place you feel air blowing is if you stand directly under the fan unit. 

 

Ours runs from 4pm until 8 am so 16hrs per day but for most of that it is modulated right down or even stopped sometimes.

Like a canal barge the house takes very little energy to move at a constant rate but a lot of time to speed up or down. A little continuous heat input is best for maintaining comfort. UFH has even more of an advantage here as it can very slowly release heat to the room if the pipes are buried in concrete or a thick screed. This can allow you to run your ASHP intermittently and best of all do the heating solely on night rate. 

 

 

1 hour ago, LeenToo said:

I am not sure i would like UFH having lived in a house with solid fuel and cold/cool floors all my life

 

I suspect you are drawing your UFH experience from high temp systems which are chronically inefficient. A well setup UFH system will be imperceptible to touch vs a well insulated floor as the floor surface will typically be only a couple of degrees above room temp. 

 

1 hour ago, LeenToo said:

Also modern tastes seems to be for houses to be 19-21 degrees C whereas I am happy with less and uncomfortable with more, that comes from living in some very old droughty damp houses in the west of ireland over the years.

 

There's nothing to stop you opening all the windows and pretending to be Peig in the miserable Irish weather if you like. Spoiler - You won't 

 

[JohnMo]

33 minutes ago, Iceverge said:

suspect you are drawing your UFH experience from high temp systems which are chronically inefficient. A well setup UFH system will be imperceptible to touch vs a well insulated floor as the floor surface will typically be only a couple of degrees above room temp.

 

2 hours ago, LeenToo said:

am not sure i would like UFH having lived in a house with solid fuel and cold/cool floors all my life.

You will read a lot about about warm floors etc, but when well insulated (house and floor) the floor remains pretty cool - very low 20s. Then depending on screed thickness pipe spacing it's response time varies. We have 100mm concrete screed (57 Tonnes) and pipes at 300mm centres. So our floor is super slow in response. Which I use to our advantage. We charge overnight on cheap rate, when the sun's out and we have excess PV electric the heat pump starts, the last few days heat pump has run for 4 to 5 hours in the day, So for every kWh spare PV electricity we convert it to 4.7kWh of heat. It doesn't overheat the house surprisingly. Floor is currently at 22.1 degs, house is at 21 degs (8 hrs after heat pump stopped) and it's 4.5 degs outside. 

 

You can't do this with an electric heater. Cooling in summer is basically free also.

[LeenToo]

8 hours ago, JohnMo said:

 

You will read a lot about about warm floors etc, but when well insulated (house and floor) the floor remains pretty cool - very low 20s. Then depending on screed thickness pipe spacing it's response time varies. We have 100mm concrete screed (57 Tonnes) and pipes at 300mm centres. So our floor is super slow in response. Which I use to our advantage. We charge overnight on cheap rate, when the sun's out and we have excess PV electric the heat pump starts, the last few days heat pump has run for 4 to 5 hours in the day, So for every kWh spare PV electricity we convert it to 4.7kWh of heat. It doesn't overheat the house surprisingly. Floor is currently at 22.1 degs, house is at 21 degs (8 hrs after heat pump stopped) and it's 4.5 degs outside. 

 

You can't do this with an electric heater. Cooling in summer is basically free also.

That sounds like a very well thought out system John, thanks for the info.

When you say you charge at night this is building up heat to send around the pipes later in the day or does that actively go into the pipes during the night? Also will it work to cool during the summer , i was under the impression that there would be issues with condensation on the floor if you used it for cooling? Sorry for my non tech knowledge I am slowly being dragged into the 21st century.......

Edited February 28 by LeenToo

[LeenToo]

8 hours ago, JohnMo said:

 

You will read a lot about about warm floors etc, but when well insulated (house and floor) the floor remains pretty cool - very low 20s. Then depending on screed thickness pipe spacing it's response time varies. We have 100mm concrete screed (57 Tonnes) and pipes at 300mm centres. So our floor is super slow in response. Which I use to our advantage. We charge overnight on cheap rate, when the sun's out and we have excess PV electric the heat pump starts, the last few days heat pump has run for 4 to 5 hours in the day, So for every kWh spare PV electricity we convert it to 4.7kWh of heat. It doesn't overheat the house surprisingly. Floor is currently at 22.1 degs, house is at 21 degs (8 hrs after heat pump stopped) and it's 4.5 degs outside. 

 

You can't do this with an electric heater. Cooling in summer is basically free also.

9 hours ago, Iceverge said:

There is some absolute crap out there so be careful what you believe and as usual the devil is in the detail. Corner your architect and find out the exact model number, the installed house heat demand and the usage patterns. Without these their info is more akin to hearsay than professional advice. 

 

The A2A is probably even more dependant on getting the right model than an A2W HP as there is tens of thousands of models and most of them are focused on cooling. The wrong model will ice up very quickly in heating mode. 

We got a Daikin FTXM25R after a lot of research. It makes noise. Probably as much as a desk fan. I wouldn't want it over my bed head but it's fine in the hall.  The only place you feel air blowing is if you stand directly under the fan unit. 

 

Ours runs from 4pm until 8 am so 16hrs per day but for most of that it is modulated right down or even stopped sometimes.

Like a canal barge the house takes very little energy to move at a constant rate but a lot of time to speed up or down. A little continuous heat input is best for maintaining comfort. UFH has even more of an advantage here as it can very slowly release heat to the room if the pipes are buried in concrete or a thick screed. This can allow you to run your ASHP intermittently and best of all do the heating solely on night rate. 

 

 

 

I suspect you are drawing your UFH experience from high temp systems which are chronically inefficient. A well setup UFH system will be imperceptible to touch vs a well insulated floor as the floor surface will typically be only a couple of degrees above room temp. 

 

 

There's nothing to stop you opening all the windows and pretending to be Peig in the miserable Irish weather if you like. Spoiler - You won't 

 

9 hours ago, Iceverge said:

 

 

9 hours ago, Iceverge said:

 

Thanks for this, just wondering why you didn't go for UFH from the start ? My initial thinking was that if I am going to build a passive house I wont need heating but I am being disabused of this notion fairly rapidly..........

Edited February 28 by LeenToo