Posted by: @sttpd1917

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The house does lose heat. If the heat is off over night during winter it'll be cold in the morning. The open fireplace in the living room is the only draughty spot in the house. Annual gas consumption is 14,313 kwh. Cavity walls are not insulated and its not an option. Loft has some insulation and more will be added. However, we've been told that this won't make much of a difference.

Thank you for taking the time to look at those numbers.

I ran a quick check using https://renewableheatinghub.co.uk/does-your-installers-heat-loss-figure-actually-stack-up/  

This is what it says: 

Based on 14,313 kWh gas annually, the implied heat loss range is 4.8-7.2 kW. Your estimate of 9 kW is above this range. Either the estimate is too high or the property has unusually poor fabric. Challenge this figure before proceeding. This is a sanity check, not a precise calculation. Note: the W/m2 check and this consumption check reach different conclusions - investigate before proceeding.

@batpred 

Excellent, thank you very much!

@batpred, @sttpd1917 

I agree with what @batpred says and would add:

Based on the fact the house cools 'significantly' at night then its possible that the loss could be >7kW, but to explain that would imply an average indoor temperature (over a period of 24hrs) of 15 or below, which means that the nighttime temperature would need to be below 10 on the coldest days. Does it get that cold?

Assuming it doesn't get that cold then its highly likely the loss is 7kW or less. Blocking up the chimney and insulation the loft will take something off giving some headroom.  You will very likely struggle to get it below 5kW though (the next size down in the Vaillant range, and most others), endorsing the HeatGeek 7kW choice.  Remember you also need a bit in reserve for DHW.  

The one note of caution is that 7kW is the sticker capacity, I dont yet have the detailed performance tables to see what the actual capacity is at your operating conditions.  It may be less, it may be more.  Presumably Heat Geek do have the capacity tables and it might be worth asking for them, or they may be going on this shortform from Vailants Czech site (which nis where you find the capacity tables for the Arotherm plus), which suggests it will likely do in excess of 7kW at -2.

If all of the above turns out to be true then further insulation (within the limited bounds you have outlined) wont change the choice of heat pump, but it will either increase efficiency or reduce the number of radiators you need to change, essentially at your option.  

S8ince rad changes are an easy retrofit I would be tempted to go with the few suggested by heat geek and see what happens.  Giving that they are offering a performance guarantee you don't have a lot to lose.

All the above is subject to the understanding that I am an amateur and base what I say on (a) what you have said and (b) my (reasonable) understanding of the physics and 3 years of sitting on this forum.  Basically there is a reasonable probability I'm talking sense but a finite probability I may not be, and its your risk.

PS I found the capacity curves here (on the Czech site again!).  Note that historically these have not included the degradation due to defrost, presumably because in Czechoslovakia it doesn't matter since you are designing for a much lower minimum temperature and drier air.

Posted by: @sttpd1917

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@batpred 

The only draughty place is in the living room, an open fire.

That will be absolutely murdering your energy efficiency unless properly abated when not in use, and it also drives losses in places you don't expect too. All the heat goes up the chimney from the ground floor, and the chimney effect (by design) sucks in air from the rest of the house, which sucks in air from outside anywhere it can find a gap.

Does the fire have a proper way of closing the chimney when not in use. If not then shove a chimney sheep or similar up it. If you do use it now and then look at what is needed so you can block the chimney when it's not in actual use. Lots of ways to keep it looking pretty, plenty of ways to close it off when not in use.

I would suggest fixing the roof insulation (really good payback), doors and maybe windows. Floors are hard to do much with although you can get some thin layers of insulation between the floor and carpet without using a jackhammer. Still not cheap. If you have tall ceilings the more eccentric approach is to insulate over the floor and lay a new floor on it but that still means adjusting all your doors and an extra step outside everywhere (plus your windows can end up with very low bases)

However if you have an open fireplace I'm not sure anything else will matter 8)

To answer the original question I've had two quotes, Octopus and a local(ish) Heat Geek installer. Both included a full list of what was included but as far as I recall neither had a breakdown of costs. I can't say it bothered me.

Not having a breakdown was not a problem in itself. The challenge was when we looked for different locations for the install, types of cylinders or number of rad swaps. We could not work with the ones that just stuck to the original price... 

@jamespa @batpred @echtedPixels

Thank you for your comments.

Don't think the fabric of the house is especially bad, its a typical 1990 house. The chimney will be dealt with and so will the loft. That should help a little bit.

Posted by: @sttpd1917

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The chimney will be dealt with and so will the loft. That should help a little bit.

We still have a gas fire for backup. The last gas engineers that visited got a bit excited when they noticed the rubber protruding and blocking the chimney. But it stops over-ventilation.. 😀 

Posted by: @batpred

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Posted by: @sttpd1917

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The chimney will be dealt with and so will the loft. That should help a little bit.

We still have a gas fire for backup. The last gas engineers that visited got a bit excited when they noticed the rubber protruding and blocking the chimney. But it stops over-ventilation.. 😀 

I'm a little confused as to what rubber you mean. Does that mean you have a rubber baffle in your chimney to stop draughts? If so, I think I'd recommend not using something like rubber otherwise you'll block airflow so much that you risk getting damp and mould issues. However, if I'm misunderstanding and you don't have a rubber baffle, I'll be interested what it actually is.

More generally, we also still have an open fireplace separate from the fireplace where our woodburning stove sits. Although the open fireplace's chimney is capped, we avoid draughts by using a chimney sheep. It's breathable so doesn't cause any dampness problems but avoids undue heat loss up the chimney. Oh, and it's biodegradable too.

@majordennisbloodnok 

We have a sort of inflatable rubber with a pipe, so there’s enough airflow to keep it dry…