That's an early date to find cavity walls in Wales @shaeney

The practice became widespread after the Great War.

What material is each leaf constructed from?

What feature(s) of the Stiebel WPL 25 made you opt for it?
Or was it the installer's preference?

Ah, perhaps all that blubber helps to insulate …. (In the ‘cavity Wales’) Sorry, couldn’t resist! 😊 Regards, Toodles.

@transparent so its weird construction.

Double engineering brick outer wall and single skin inner wall. Our buyers inspection engineer said the walls were bombproof!

Makes for very deep window recesses.

Went for Steibel because the high efficiency and high output.

That's a really sturdy outer leaf!
It's unusual to find such an over-engineered approach... especially as it's the inner-leaf which supports the roof.

As for the Steibel - are you actually achieving the level of efficiency you were after?
Have you got a controller which tells you the COP?

@shaeney welcome to the forums. So I simply must ask given the amount of articles that persist saying that heat pumps don't heat old buildings, especially with no/little insulation. Are you warm and what are your running costs like? Did the Stiebel replace an oil boiler?

@editor Steibel replaced an old gas boiler.

When we bought house, boiler needed replacing. We wanted all the radiators gone off  kitchen walls, so wanted under floor heating......

So we ripped up downstairs floors, put under floor in and went with a Heat Pump. just 2 rad changes needed upstairs, rest were already oversized. 

Downstairs is mainly open plan but we do have a log burner mainly for really cold winter nights, but its for the look and feel more than heat. heating keeps up even at -6 the other night.

Running costs is about half what gas was, I estimate, but thats mainly down to the cheap overnight tariff.  So I heat the underfloor mass etc with cheap energy.

I think people say you need COP of 3 to "break even" at 7p gas and 30p leccy, so I am above COP 3, then factor in average I pay for leccy is around 16p (I think), it makes a huge saving.

@shaeney super interesting. In the absence of insulation, I’m very curious to hear what the heat loss survey was. Can you walk us through that? Also what was the target temperature? 21C?

@editor the main living room is approx 30m2 with a design temp of 21 degrees at 74w/m2 for a total of 2,264. No idea how that compares to anyone else!

Theres a LOT of glass in that room with 1 set of French Doors and a triple bifold. Ceiling height is around 8 and a half foot 

Total area of living space is 185m2

Posted by: @shaeney

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I heat the underfloor mass etc with cheap energy.

For clarification @shaeney
so that UFH pipe is all running through a new solid/concrete floor, correct?

Concrete thickness?

Insulation below it?

I suspect that approach allows your heat-pump to operate more efficiently.
The high thermal mass, slowly heating over many hours will diminish/eradicate the HP from cycling.

Here's part of my house with the UFH pipe stapled to insulation prior to the concrete pour.

@editor -- it would be great if this could in some way be reflected in one of the heat calculators you're contemplating for this site.

But I'm unsure how to achieve that.
It needs input from one our tame HP physicists/engineers 🙂 

It would be a useful feature for members here to evaluate the different efficiencies which be obtained depending on how they implemented the heat-emitting elements for their home:

• radiators
• UFH (suspended floor)
• UFH solid floor with high thermal mass

Maybe this would be better illustrated with a theoretical house, rather than the householder putting in their own details.

@transparent so the old flooring came out, down about 8 inches, I think.

Then 4 inches of insulation went down, foil side up. The underfloor heating coils were secured to the foil side, then a few inches of "biscuit mix" screed went down over the top

Probably a total of 70m2 underfloor heating went in. Abut half is covered with quick step laminate, the other half with tiles

Great. That's what I'd imagined @shaeney
Got any photos during the works?

Was this all DIY, or did you buy in contractors?

I have tiles in the kitchen area, and engineered oak boards over the rest.
But it was more complex because that oak boarding spanned across to an area with suspended floor, running across joists. 😲 

Did you fix your laminate to the screed to increase the heat-transfer?
Or does it 'float'?

I consulted Bostik technical support, who recommended a primer and an adhesive "Laybond Wood MS Polymer".
That's proved very successful, despite my fears of differential expansion rates.
Bostik really know their stuff!

Details are useful here on the forum.
Others will come across this topic in months/years to come and be able to copy the best practices from what we've achieved.