@johnmo 

Very good point.

It’s something I should have given a lot more consideration.

I will contact my contractor to ask if it’s possible at this stage to change the open fire in this room to a sealed stove. I know it has been built to accommodate a fireback and has the lintel etc in place.

Even though GSHPs are more expensive upfront, they generally offer a longer lifespan than ASHPs and significantly better SCOPs when well designed.

@barry-sharp, for example, has a system in Scotland achieving a SCOP of over 4.5, and if your budget allows, it’s definitely worth considering ground source seriously.

Yes, heating oil is currently around 50p per litre, but as we head into late autumn and winter, it’s likely to climb back toward 70p or more. In that context, a well-designed GSHP will almost certainly be far cheaper to run in the long term.

Posted by: @gcon45

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open fire in this room to a sealed stove.

When looking at room sealed stoves, you need to ensure primary and secondary air are taken from outside - some only take primary air from outside and secondary from the room.

Room sealed should only need a 100mm hole through the wall and this is then ducted to stove.

Posted by: @gcon45

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I can try and find any bits of info that anyone thinks would be beneficial though?

The useful bit is the bit that specifies the heat loss at the design temp ( presumably around -3).

It's your choice of course but I genuinely fear that whoever is designing your heating system may be specifying something that you will not be happy with. 

I have no axe to grind, I'm not involved with the industry I'm just an interested amateur with a background in phisics who happens to have evaluated carefully what's been said here for the last two years and, as a result, has ended up with a very satisfactory ashp experience mosty by avoiding  installers that frankly were talking BS and being very careful about system sizing.

Posted by: @gcon45

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Yeah the flue for the fire will be sealed up for about 360 days of the year with a draught excluder.

It’s a traditional house so it’s in keeping with the style.

I’d imagine the fire will only ever be actually lit around Christmas time.

We have a cassette style inset stove, much more efficient than an open fire, which is less than 5kW so doesn’t require any deliberate ventilation. It is a Stovax but the model isn’t important. With the door closed there was no discernible air leakage when we had the whole house leakage measured.

Our MVHR endures ample ventilation if we were nervous about CO with the fire lit. The fire really is just a visitors on special occasions usage and when we feel like it, since the novelty wore off a while ago back.

So your multi-fuel stove will have no leakage to speak of leaving only the open fireplace extra to a well insulated modern house. Our 200m2 50s house needs a 7kW heat pump which keeps us nicely warm. You are unlikely to to need much above 12kW!

So is that with external air supply?

@johnmo  no external air supply, just the room air. We do have CO detectors and never had any alarms.

But the measured flow on the MVHR system vent provides enough air flow

Posted by: @judith

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@johnmo  no external air supply, just the room air. We do have CO detectors and never had any alarms.

But the measured flow on the MVHR system vent provides enough air flow

Braver person than me. No way I would go down that route.