Stone house and air source heat pump

[Barefootliving]

Hi all

We are renovating a 1915ish stone rubble house. It has not been lived in for 14 years and is just a shell needing complete renovation. It has a lot of damp - we will be removing the external cement render and then render with lime, remove the internal gypsum plaster and replaster with lime, add aco drains to ensure any surface water does not reach the house, remove the concrete floors and replace with a limecrete system. We are hoping this will address the damp.

As we will need to put in a heating system we are hoping to go with an air source heat pump but are aware of the need for good insulation. If we have an insulated floor with ground floor underfloor heating, roof insulation, and new double glazing will the heat produced/insulation be sufficient if we use wood or cork board under lime plaster internally? We had also looked at spray hempcrete but the rooms are very small already for a thick layer of this plus lime plaster and if we used hempcrete externally we would need to extend the roof overhang and replace the whole window units to allow for the thickness of the hempcrete spray plus lime render (the roof looks like the only thing that we can keep right now so reluctant to replace if wood fiber or cork board insulation internally would be sufficient). We have a tight budget so cost is a consideration.

We would probably just put cheap electric panel radiators upstairs if building control requires it (we hope to add solar panels to keep electricity costs down).

Any experience of putting an ASHP/UFH heating in a stone rubble house much appreciated.

Many thanks for your thoughts and advice.

Tamsin

 

[paulc]

A heat pump is just another source of heating. As long as the whole system is properly specified, it should work out as cheap to run as a gas or oil boiler. Tuned for efficiency, and on the right tariff, it could even be cheaper over the course of a year.
Heat pumps work very well with underfloor heating, but before you go splashing out money on installing UFH, seek input from a heat pump expert. He/She will be able to guide you through layout and sizing of pipework and make recommendations as to radiator sizes in the rooms where they are needed. Proper wet radiators upstairs will be three or four times cheaper to run than electric panels - With decent double/triple glazed windows, you can mount radiators on internal walls to rationalise pipe runs.
I fitted low E DG windows here a couple of years back and have since moved all radiators to internal walls. Don't notice any curtains of cold air from the windows, and the place heats up just fine to a decent temperature. Also get a decent amount of solar gain from a large south facing bay window which helps to reduce heating costs when the sun shines in winter.

For a heat pump expert, I'd suggest seeing if you have a Heat Geek in your area and have some discussions with them. It may cost a few quid for a consultation, but it would be money well spent. Beyond that, the only other thing to add, is to use a really low design flow temperature (40°C tops). That will maximise efficiency and keep the annual running costs low.

 

[Barefootliving]

Many thanks for your thoughts. I will definitely look into whether there is a Heat Geek near us. I’m just worried we won’t be warm enough with stone walls, even if we do apply some insulation in the form of wood fiber boards.

 

[Lacan07]

Hi all

We are renovating a 1915ish stone rubble house. It has not been lived in for 14 years and is just a shell needing complete renovation. It has a lot of damp - we will be removing the external cement render and then render with lime, remove the internal gypsum plaster and replaster with lime, add aco drains to ensure any surface water does not reach the house, remove the concrete floors and replace with a limecrete system. We are hoping this will address the damp.

As we will need to put in a heating system we are hoping to go with an air source heat pump but are aware of the need for good insulation. If we have an insulated floor with ground floor underfloor heating, roof insulation, and new double glazing will the heat produced/insulation be sufficient if we use wood or cork board under lime plaster internally? We had also looked at spray hempcrete but the rooms are very small already for a thick layer of this plus lime plaster and if we used hempcrete externally we would need to extend the roof overhang and replace the whole window units to allow for the thickness of the hempcrete spray plus lime render (the roof looks like the only thing that we can keep right now so reluctant to replace if wood fiber or cork board insulation internally would be sufficient). We have a tight budget so cost is a consideration.

We would probably just put cheap electric panel radiators upstairs if building control requires it (we hope to add solar panels to keep electricity costs down).

Any experience of putting an ASHP/UFH heating in a stone rubble house much appreciated.

Many thanks for your thoughts and advice.

Tamsin

As Paul says I'd consult widely before going down the heat pump route. They'll be just as many detractors as supporters out there. I briefly considered an air to air system. How thick are your stone walls? I'm not sure you'll be able to get your walls insulated enough with natural materials to get the benefits of a heat pump.

 

[Barefootliving]

Yes, that’s my worry - would so like to go the eco route if we can but don’t want to end up in a cold house

 

[Flyfisher]

I've no experience of heat pumps but I've installed 'wet' UFH in the C17 rubble-wall addition to our timber-frame house. The wall thickness varies but is at least 12 inches and up to about 18 inches in places. To be honest, I didn't really do any design work because the pamments-on-earth floor was being reworked anyway, using foamed glass and limecrete (details on the Mike Wye website) and the addition of UFH pipework was a relatively trivial additional expense when done at the same time. It was a couple of years before we actually plumbed them into the heating system and were pleasantly surprised to discover it can easily get the room up to 19C, although the thickness of the screed and pamments means that it can easily take 12 hours to fully warm the room when starting from cold. The reverse is also true when cooling down of course, so this time lag is not really an efficiency issue as such. The room is quite large (about 6x8m) with three outside walls that are just lime-plastered and not insulated. However, 12-18 inches of dry rubble wall must surely have a reasonable insulation factor, I've just never bothered to run the numbers.

I'm certainly pleased with the result because the difference between a completely unheated room (as it was) and even running the UFH at around 12-14C makes a huge, huge difference and means that the woodstove can get the room up to a comfortable temperature very quickly indeed. Basically, the gentle heat seeps into the entire fabric of the room - floor (obviously), walls and ceiling rather than having a few 'point-sources' of higher temperature appliances.

When we first took on our project, I looked into heat pumps (ground and air source) and was very keen until I discovered we could get a connection to mains gas for £300, at which point all the other options fell by the economic wayside. But times change and who knows what the future will bring? The important thing, I'd say, is to lay UFH pipework whenever easily possible even if they are not used immediately.

Meanwhile, if talking to heat pump suppliers and digesting their no doubt encouraging sales pitches, I would ask if they have any reference sites of happy customers who are willing to let you experience how these things work in a real home?

 

[paulc]

I would ask if they have any reference sites of happy customers who are willing to let you experience how these things work in a real home?

Well, there is a web site for that: https://www.visitaheatpump.com/

When I was replacing my heating system, I did consider a heat pump. But at the time, to qualify for a Boiler Upgrade Scheme would have required doing EPC upgrades which would have put the whole thing well above budget. A few months later, the government removed the requirement, so I did a "what if" with Octopus. The price they quoted was on par with what I'd paid for a gas boiler and would have included a bunch of new radiators. Kinda wish I had waited...

 

[Barefootliving]

Thank you for all your thoughts. This is very helpful. We’re going to get some more information on how much difference a layer of wood fibreboard on the walls will make in terms of insulation

 

[Flyfisher]

When I was replacing my heating system, I did consider a heat pump. But at the time, to qualify for a Boiler Upgrade Scheme would have required doing EPC upgrades which would have put the whole thing well above budget.

In the context of global warming, climate change and saving the planet etc, am I the only one who thinks that restricting these sort of energy efficiency schemes to the top EPC tiers (A, B or C I believe?) is somewhat illogical?

For example, many of us on here live in old, draughty houses that typically require more energy to heat to a reasonably habitable temperature. But if we use non-fossil fuel derived energy then there is no climate change impact as I understand things. So why not subsidise solar PV installation in draughtly old houses with low EPC ratings to run heat pumps so that their inherent energy inefficiency is not contributing CO2 into the atmosphere? Why limit this approach only to houses that are already energy efficient?

 

[NecessaryWing]

My understanding is that air to water heat source pumps need good insulation because the temperatures they work at are so low. Therefore, with old draughty houses, you would either have a cold house or a warm house with a poor COP.

However, I don’t see why air to air heat pumps wouldn’t work. They heat the air directly so wouldn’t be confined to well insulated homes. Latest models have very good cop values. They also double up as air conditioning units. Last I looked the government are considering giving grants for air to air too.

People I’ve known who have installed them have cheap heating and air conditioning with very high COPs. Only downside is you need more heat pump units on the exterior walls which, for lovely homes like ours, is a bit of an eyesore.

However, I think they are good on exterior walls that are not on show as a hybrid approach.

Has anyone tried air to air in an older property?

 

[NecessaryWing]

But if we use non-fossil fuel derived energy then there is no climate change impact as I understand things.

It’s definitely hugely improved but they don’t have no climate impact. They run off electricity and roughly 50% of the UKs national grid is still powered by burning gas - it varies depending on wind speeds etc so can be lower or higher. https://grid.iamkate.com/

I agree with the needs for better grants to encourage solar given the gravity of the climate situation currently.

 

[Lacan07]

My understanding is that air to water heat source pumps need good insulation because the temperatures they work at are so low. Therefore, with old draughty houses, you would either have a cold house or a warm house with a poor COP.

However, I don’t see why air to air heat pumps wouldn’t work. They heat the air directly so wouldn’t be confined to well insulated homes. Latest models have very good cop values. They also double up as air conditioning units. Last I looked the government are considering giving grants for air to air too.

People I’ve known who have installed them have cheap heating and air conditioning with very high COPs. Only downside is you need more heat pump units on the exterior walls which, for lovely homes like ours, is a bit of an eyesore.

However, I think they are good on exterior walls that are not on show as a hybrid approach.

Has anyone tried air to air in an older property?

I looked into it a bit - an external unit heating the ground floor. The COP is key as you'll wind up using more electricity/money defrosting the thing in winter than a gas boiler ever would. From what I can gather self-install is off the table and don't bank on the government funding you, that's not happening.

 

[montyjohn]

In the context of global warming, climate change and saving the planet etc, am I the only one who thinks that restricting these sort of energy efficiency schemes to the top EPC tiers (A, B or C I believe?) is somewhat illogical?

For example, many of us on here live in old, draughty houses that typically require more energy to heat to a reasonably habitable temperature. But if we use non-fossil fuel derived energy then there is no climate change impact as I understand things. So why not subsidise solar PV installation in draughtly old houses with low EPC ratings to run heat pumps so that their inherent energy inefficiency is not contributing CO2 into the atmosphere? Why limit this approach only to houses that are already energy efficient?

My house has a heat loss of around 32kW. About 50% of that is air changes. Bit of a finger in the air (didn't mean that pun) as not been tested for air tightness, but all other losses are accurate. Air changes could easily be double the assumption.
I have insulation improvement in mind, but waiting for feedback from the conservation officer.

My only automated source of heat is a tiny Rayburn which kicks out about 8kw to the room and radiators upstairs combined. So my radiators upstairs are luke warm. It runs 24/7 and upstairs isn't too bad in terms of room temperatures, even now with ice outside I'm at about 17 degrees.
Fortunately I have quite a few fire places downstairs, so with effort no issues warming the place up during this cold snap.

Spoke to a few local installers for ASHP a couple of weeks ago and they said I can't get the BUS unless the system they install meets my my whole house heatloss.

This would mean installing a 32KW (or maybe larger) system which would need to be three phase, which I don't have.

Basically, the costs just get carried away. Probably looking at £30k all in. Not going to happen.

So I am now fitting a 32kw second hand oil boiler.

It may still switch to ASHP in the future when upgrades are done, and if the BUS is still available.

What I wanted to do is fit say a 15kw ASHP (as I believe I can get heatloss down to that) and I will just make up the difference with fires as I am doing anyway.

I will still have more heat than I have now, and will release far less CO2.

But no, it's not to be.

 

[fernicarry]

This would mean installing a 32KW (or maybe larger) system which would need to be three phase, which I don't have.

Not sure where we are currently in terms of unit pricing but circa 9p for gas and 28p for leccy last time I looked. Therefore for a HP to break even on running costs you'd need a COP of about 3 or better. 32kW output would be about 11kW input which is possible on single phase. Whether such a machine exists is a different question and if it does it certainly won't be cheap or particularly subtle. I imagine the DNO's aren't all that keen on a single phase running at 50A for hours on end so that's probably why it has to be 3 phase.

I'm in the same boat. 35kW gas boiler, heat loss well in excess of that in this weather I can confirm shivering as I type. Too early to light up the Aga, we try to get as close to Xmas as possible before doing that. We do have a 3 phase cable head but single phase meter and internal wiring, something I am picking away at bit by bit.

None of the net-nothing plan is aimed at us. We are at the end of a very long tail of hard to address cases. The green zealots would happily see our properties bulldozed and replaced by polystyrene boxes (provided they were electric bulldozers of course...). The very idea of providing assistance to those "rich" people in their big/nice houses is anathema to them. We're on our own. Better get used to it.

On the bright side, as our property values plummet due to their prodigious energy needs, at least we'll avoid the mansion tax...

 

[montyjohn]

Not sure where we are currently in terms of unit pricing but circa 9p for gas and 28p for leccy last time I looked. Therefore for a HP to break even on running costs you'd need a COP of about 3 or better. 32kW output would be about 11kW input which is possible on single phase.

With an EV tariff you can do a little better than that. Foe example Octpus offer:

Night rate (23:30 - 05:30) 7p

Day rate (05:30 - 23:30) 29.86p

If you run an ASHP 24/7 that would be an average £0.24 per kwh

With some decent battery storage you could get this down a lot further. Obviously not for a 32kw ASHP, batteries would be ridiculous, but for a 15kw one, you could get a lot closer to th 7p per kwh (2.3p per kwh of heat).

The very idea of providing assistance to those "rich" people in their big/nice houses is anathema to them.

The irony here is I moved out of a three bed ex-council semi-detached and moved into a listed property that was £70k less than the house I moved out of.

I imagine the DNO's aren't all that keen on a single phase running at 50A for hours on end so that's probably why it has to be 3 phase.

The issue is, if you have a constant 50a, and then you have a tumble dryer going and you switch a kettle on whilst boiling some water for your eggs it's pretty easy to get close to 100a. One installer said they could add multiple ASHPs in a cascade system that are all single phase, but it's complicated.
I also don't want to spend £3.50 an hour on electric to run a huge ASHP system, I want to lower heatloss, and will one day, but appreciate it will take a few years.

 

[paulc]

I'm in the same boat. 35kW gas boiler, heat loss well in excess of that in this weather I can confirm shivering as I type.

The size of the gas boiler is only part of the equation. To get all of that energy out to heat the property, you also need sufficient radiators big enough to radiate that heat.
If I add up the rated heat output of every radiator here, it comes out at about 13.5kW (at a 70°C flow temperature or ∆T50) - This is pretty close to what the heat meter connected to the boiler indicates.. Boiler is rated at 28kW, so have plenty of headroom should I want to add more radiators.

With an EV tariff you can do a little better than that. For example Octopus offer:
...
I also don't want to spend £3.50 an hour on electric to run a huge ASHP system, I want to lower heatloss, and will one day, but appreciate it will take a few years.

Octopus also do a Cosy tariff specifically aimed at heat pump users, and I suspect other suppliers will have similar offerings. So on a suitable tariff, even with a COP of 3.0, running costs should be lower than a gas boiler.

Also been working on reducing heat losses here, Got to the stage where 5-6kWh is enough to raise the temperature by 1°C per hour, and it takes about four hours to lose that 1°C rise.

 

[fernicarry]

it's pretty easy to get close to 100a

Unlikely you'd add another continuous 12kW from your domestic appliances, diversity and all that. And the fuse doesn't go pop at exactly 100.1. An EV charger though would get you well on your way. That said not all cut outs are 100A, many are 80 or 60. Not saying I recommend running it that close to the limit. And, yeah 7 quid an hour (25kWh) would be less than desirable...

I'm not really a believer in those split rate tariffs. If you have huge thermal mass in your system so that you can fill your boots during the cheap window and then coast for many hours then maybe. I know some people on here can do it, but I don't think that's your typical period property, or even any typical property built more than 20 years ago i.e. almost all of them. We really shouldn't need to be gaming the system with exotic tariffs and local energy storage in order to make net-zero stand up to scrutiny.

 

[Flyfisher]

The very idea of providing assistance to those "rich" people in their big/nice houses is anathema to them. We're on our own. Better get used to it.

On the bright side, as our property values plummet due to their prodigious energy needs, at least we'll avoid the mansion tax...

The irony here is I moved out of a three bed ex-council semi-detached and moved into a listed property that was £70k less than the house I moved out of.

These are good reasons why property taxes are unfair because apart from the fact that they have already been purchased out of already-taxed income, they are not based on an ability to pay. The classic example is the hard-working person who has worked and paid taxes all their life in order to buy a comfortable home for their retirement and then, when their income drops significantly, finds that they cannot afford to pay a 'mansion tax' on their home, even though it's nothing to do with them that its value might have gone through the roof.

But we should probably avoid politics!

 

[larry]

In the context of global warming, climate change and saving the planet etc, am I the only one who thinks that restricting these sort of energy efficiency schemes to the top EPC tiers (A, B or C I believe?) is somewhat illogical?

For example, many of us on here live in old, draughty houses that typically require more energy to heat to a reasonably habitable temperature. But if we use non-fossil fuel derived energy then there is no climate change impact as I understand things. So why not subsidise solar PV installation in draughtly old houses with low EPC ratings to run heat pumps so that their inherent energy inefficiency is not contributing CO2 into the atmosphere? Why limit this approach only to houses that are already energy efficient?

I do agree entirely with the logic here. One large old house might have the carbon emissions of ten well insulated smaller ones.

But I also suppose it makes sense to incentivise people with the big houses to do as much as they reasonably can to improve their thermal efficiency... And perhaps those big gas/fuel bills might help with that.

We've had real success with 'project insulation' l. Year 1 in our house we used 24000 kWh gas, but with wood fibre insulation (and lots of other changes, smart thermostats and MVHR probably most significantly) we got down to 9000kwh last year. Still have a gas boiler, but actually the improved energy efficiency reduces the potential benefits for planet earth of swapping out to an ASHP (poorly worded so I hope that makes sense)

 

[NecessaryWing]

I looked into it a bit - an external unit heating the ground floor. The COP is key as you'll wind up using more electricity/money defrosting the thing in winter than a gas boiler ever would. From what I can gather self-install is off the table and don't bank on the government funding you, that's not happening.

Some of the top manufacturers are quoting cops of 3+ for UK winter taking the defrost cycles into account. So you would at least break even with gas/oil price per kWh vs electricity. With incredibly hot summers the air conditioning double up would be very good too. Cop values as air cons units in the summer are even better especially if one has solar panels too.