Heat pump retrofit

DrPhilG · 20-03-2021 2:57am #1

Is a ground source heat pump system retrofittable, and is it ever likely to make financial sense?

I have a 1950sq ft bungalow, currently heated by oil. I also have 6.2kwp solar array with a plan to double that in the future. I have a 0.8 acre site with about half of that being lawn so a horizontal ground source system could be fitted.

I understand that insulation is important as the heat pump can use a lot of electricity. My house is pretty well insulated in the attic, but the walls only have aeroboard rather than pumped bead insulation.

Any ideas on cost for installation and running? I would likely have no problem running the system 8 months of the year but if the electric costs are sky high during the winter, and solar production is low, would it negate the savings I'd make in the rest of the year?

Any info would be appreciated.

Patmwgs · 20-03-2021 9:32am

Hi phil, its the other 4 months of the year that you will really need it.

KCross · 20-03-2021 12:34pm

DrPhilG wrote: »

Is a ground source heat pump system retrofittable, and is it ever likely to make financial sense?

Yes for the former.
Probably no for the latter.

What you do is first spend your money on more insulation and making the house airtight and heat recovery ventilation and upgrading windows and doors.

If you get all that done I’d bet your oil bill would be so small it would make the economics of retrofitting a HP very dubious.

i.e. Doing the HP first is a bad idea. Insulate and air tightness first. Then evaluate.

slave1 · 20-03-2021 2:20pm

I agree, insulate insulate insulate, with the weather all this week we have no heating on and that's with bedroom windows open all night and morning.
Insulate to the hilt and heating really becomes minuscule...

DrPhilG · 20-03-2021 2:54pm

I was looking at changing my windows. Around €8k to change everything to double glazed laminated gas filled.

I already doubled my attic insulation.

I'm wary of bead pumping the walls. Too many horror stories of damp coming in on any walls exposed to extreme weather, which our bedroom wall regularly is.

Water John · 20-03-2021 3:48pm

DrPhilG wrote: »

I was looking at changing my windows. Around €8k to change everything to double glazed laminated gas filled.

I already doubled my attic insulation.

I'm wary of bead pumping the walls. Too many horror stories of damp coming in on any walls exposed to extreme weather, which our bedroom wall regularly is.

Is this from the drill holes not being sealed?

Dtp1979 · 20-03-2021 4:04pm

Water John wrote: »

Is this from the drill holes not being sealed?

No, from moisture passing along the beads creating a bridge from the external block to the internal. I don’t know how they overcame this problem. I think it was the main reason the cavity was 4” but only 2” was insulation, kept against the internal block.
Nowdays there entire cavity has 4” insulation but there’s a plastic coat on the insulation board against the block

slave1 · 20-03-2021 4:20pm

DrPhilG wrote: »

I was looking at changing my windows. Around €8k to change everything to double glazed laminated gas filled.

I already doubled my attic insulation.

I'm wary of bead pumping the walls. Too many horror stories of damp coming in on any walls exposed to extreme weather, which our bedroom wall regularly is.

You've a bungalow, would you consider external insulation DIY, much much easier without scaffolding etc, just get a plasterer to render

DrPhilG · 20-03-2021 4:36pm

slave1 wrote: »

You've a bungalow, would you consider external insulation DIY, much much easier without scaffolding etc, just get a plasterer to render

Always thought of it, also extraordinarily expensive mind you. But likely cheaper than a heat pump though.

DrPhilG · 20-03-2021 4:37pm

Water John wrote: »

Is this from the drill holes not being sealed?

No, dtp1979 hit the nail on the head. Bridges the gap, and when you have a very exposed end wall like me it can lead to damp.

Patmwgs · 20-03-2021 5:46pm

Did you double glaze existing frames or renew? You could fit 50 to 70mm good quality pink insulation boards on your internal gable wall and reskim. Cheapest option. But will need to add some ventilation as it will cause mould. Or do all internal skin of external walls and add a heat recovery unit to a bungulow is easy enough.

DrPhilG · 20-03-2021 6:22pm

I dry lined the bedroom wall last year when redecorating. That's the biggest room of the coldest external wall.

Calahonda52 · 20-03-2021 6:29pm

DrPhilG wrote: »

Always thought of it, also extraordinarily expensive mind you. But likely cheaper than a heat pump though.

If doing EWI in an exposed aspect, you need a separate rain shield

Patmwgs · 20-03-2021 6:43pm

You could double up on your ceiling joists and fit a minimum of 300mm insulation. You can still board it out for storage.

Dtp1979 · 20-03-2021 7:18pm

There’s other stuff you can get poured into walls that aren’t beads. Like liquid that expands that has excellent thermal resistance. Can’t for the life of me think what it’s called

DrPhilG · 20-03-2021 7:38pm

Patmwgs wrote: »

You could double up on your ceiling joists and fit a minimum of 300mm insulation. You can still board it out for storage.

Already done. Added a second level of joists and doubled the insulation a few years back.

MicktheMan · 21-03-2021 12:19am

Dtp1979 wrote: »

There’s other stuff you can get poured into walls that aren’t beads. Like liquid that expands that has excellent thermal resistance. Can’t for the life of me think what it’s called

Sounds like BALL LITE maybe? If so, then watch out for cracking of the masonry:(

listermint · 21-03-2021 8:48am

DrPhilG wrote: »

No, dtp1979 hit the nail on the head. Bridges the gap, and when you have a very exposed end wall like me it can lead to damp.

This has not alot to do with a cavity bead rather alot more to do with broken or rubbish external render, broken or poor guttering / roof slate or tile and or poor drainage or items pushed above the dpc level.

Patmwgs · 21-03-2021 12:59pm

I agree with listermint, alot of fallen cement on to wall ties can carry moisture across cavities. You would normally try and build the inner course slightly higher for water not to cross over. But the newer stainless steel ties have overcome alot of this. The older plastic ties were alot wider, so could catch alot more cement. A good builder would keep the cavity clean.

Heat pump retrofit

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