@editor  Very well and I was impressed, right or wrongly re the price, but we shall see in time.  I have attached a part of the letter from the guy who attended.  Observations welcome.  My first foray into this dark world and I had no preconceived idea how much it might cost but this is certainly not beyond or stretching our means.  Remember we don't even have pipework installed let alone any radiators so this is a complete start from scratch.

@morgan, good to see it's very similar to mine (same supplier) apart from the ASHP itself, the fact I'm having 2 zones and a bit more pipework for 3 showers.  We even have 12 rads like you although ours might be a little bigger since our heat load is just over 20000 kwH.  Out total was a smidge over £16k.  I also had a couple of remote estimates based on a floorplan and EPC they were slightly more (but in the same ballpark).

@kev-m

Interesting.  Did you have any preconceived idea of cost.  Were you surprised, shocked, disappointed or pleased? 
For us to install oil fired CH we would need the boiler plus all rad’s and plumbing.  Rough ball park estimates put the cost at more than half of ASHP but without 10k coming back via RHI.  So, as long as I can be convinced this is the right option in terms of it being efficient (warm enough), friendly (quiet enough) and gives me the same hot water pressure as the cold (hot water pressure here is soooooo poor) then it’s bit of a no brainer.  The only absolute re taking the oil fired option is the CH will def’ work and be efficient.  But it won’t improve my hot water pressure and will be more expensive in the long term with the lack of RHI and fossil fuel costs only set to spiral.  Much food for thought. 🤔

I was pleased at the cost; it was at the lower end of my expectation.  I briefly looked at oil and I thought it would cost £10-12k and we'd have to find somewhere to put the tank and boiler.  I also can't see oil getting cheaper in the long term but it's the RHI that clinched it for me and also the warm glow of doing my bit for the environment.  I have some pastimes I really need to carbon-offset.  😉 

@kev-m

Interesting application a few weeks ago showed an ASHP installed in a terraced house in Wales.

Great output figures and efficiency and probably kills off the argument regarding using heat pumps in terraced housing for good.

It fits in with Kev's comments as, obviously, two of the walls are shared with neighbours so the heat loss is levelled out somewhat.

I will post on here or send to Mars for a appropriate slot on the Hub. Well worth it, even if it wasn't an LG system.

@bobbt9866, in very practical terms I would have thought terraced houses would benefit more from heating efficiency, as opposed to detached properties, so am also thinking along Kev's lines.

Derek M and others - I was trying to work out the heat loss from my bathroom, which currently has a 120W electric towel rail, no thermostat.   Over the last couple of days when it's 9 deg outside it's been 19 in the bathroom with the door shut and the rail on. It's 19 degrees in the adjoining rooms too so can I conclude the heat loss through the one external wall/window, floor and ceiling is 12W/degree?  And therefore at 0 deg external it would take 12x19 = 228W to maintain 19deg.  Or 240W for 20 deg.  But then I'd have to have either assume the surrounding rooms were 20 deg too or take heat loss to/from them into account.  Or I could scale up my bathroom and work out a number for the whole house, assuming it has the same floor, ceiling, windows, faces the same direction, etc. Or I could have got this completely wrong and be talking rubbish...  

@editor

The general myth out there is that Heat Pumps cannot work in terraced housing due to their size and the extra equipment. This case history, which includes great data, disproves it totally.

Hi Kev M,

Accurately estimating heat loss either by calculation or more practical methods, is an almost impossible task. There are so many variables, all of which would need to be taken into account to produce a truly accurate result.

This is why it is necessary to get as close as possible to an accurate value in the worst case scenario, and then add 10% or 20% to the size of the heat emitter. With suitable controls it would then be possible to maintain a desired temperature under all expected operating conditions.

In your particular example, were the readings taken at one period in time or over an extended period? Because there can be quite long delays between changes in outside temperature and the effect being seen inside, it is always advisable to take readings at say 1 hourly intervals over an extended period. This would also give a more representative estimation of the heat loss under different conditions.

I have noticed from monitoring the performance of our heating system, that maximum heat loss normally occurs around sunrise, even though the outside air temperature may have already started to increase.

I am sorry that I cannot give a more definitive answer. All I can say is that the more data that you collect, then the more accurate your estimation should become.

@bobbt9866, that's interesting. Would love to see if we can get some of that data published. Should make for an interesting read.

I think we could have a simplistic approach to this. If you are lucky and upgrading then its best is to start from a working model, for example I had a gas boiler rated at 37 kWh installed back in 1992 with efficiency rating at ~60% - which is equivalent to ~15 kWh considering an average CoP value of 2.3 for the ASHP.

I designed and engineered my own setup by installing a 16 kWh ASHP back in April' 2019 with a separate DHW tank heat pump - the ones that have the heatpump on the top of the tank - my main reason to have it separate was to dehumidify and cool the house in summers, and vent the cold out in winters.

It has worked great though the contractors had recommended something based on some excel or application where you input those complex numbers that was either too under powered or too over powered. From my experience none of the recommendations hit the target. This is my second winter with lowest temperature of (-22) recorded without a struggling ASHP.

Assuming we are getting novices reading these posts who are not versed in the Black Arts of heating, it might be worth noting that a budget sizing method to 'give a clue' is 100Watts per m2.

Not rocket science but it puts the owners within the ball park when they call in an actual Heating Engineer.