If it was my house before start thinking about heating systems I would see how best I could insulate the walls. Regardless of how efficient HP are, they still use energy which needs paying for despite RHI payment. The smaller your HP needed the better. Bore holes are expensive ASHP noisy if not sited properly. What scope have you to insulate the walls internally or externally and what about the floors. I think to take a fabric first approach (Insulation, elimination of cold bridges and elimination of air leakage) is where I would start. Spending money on these areas is there for ever, a once off cost, whereas any heating system requires repair, maintenance etc and the smaller and simpler the better. Once you have worked out what you can achieve with this approach go back to the calculation to see how much energy is needed to heat the house.

Posted By: lookseehearDoing some calculations on the heat loss calculator ( https://www.resurgence.org/resources/heac.html ) seems to indicate that the total heat lost during a typical year might be in the region of 35,000 kWh

Hmm, that calculator says the heat loss from my house is 14,888 kWh per year. PHPP says it is a maximum of 2,160 kWh, and it's much closer to the truth. I was pleasantly surprised that it allowed me to say my house was built from straw bales but not so pleased by its reluctance to let me enter triple glazing, or underfloor insulation or even 450 mm of roof insulation. So I'd take everything it says with a big pinch of salt.

IMHO, a better approach would be to ask the vendor for a copy of their heating bills, and some idea of how warm they keep the house. Given the time of year and where you are in the house-move cycle, I would suggest the following plan:

(1) Get to completion on the transaction and move in
(2) Try to enjoy Christmas
(3) Sort out whatever turn out to be the most urgent deficiencies of the house
(3a) Hopefully not the oil heating
(4) Subscribe to PH+ magazine - the current issue has a good Enerphit refurb

Meanwhile, and while waiting for an end to the covid confusion:
(1) Get or make some accurate floor plans and elevations of the house and make several copies
(2) Decide on how you will plan to install some ventilation (preferably MVHR)
(3) Decide on your airtightness strategy
(4) You can start on the MVHR and airtightness anytime after this
(5) Decide on your goal (PH, Enerphit, AECB Gold, Silver etc etc)
(6) Decide details of your insulation plan
(7) Only after the previous step will you be able to work out how much heat you will need and start to think about how you might obtain it
(8) Decide how to implement all the plans
(9) Do it

Hi all,

Thank you so much for all your input so far. I'm definitely getting that insulation is preferable, there are a few reasons why we aren't massively keen which I'll try to set out below, but they focus around the fact that this is an old house (here it is https://www.rightmove.co.uk/property-for-sale/property-84497702.html).

From what I've read about internally insulating stone houses, by creating a warm box inside a cold house, the external walls are much less likely to dry out properly after cold wet weather, and that can cause accelerated damage to the fabric of the walls (freeze/thaw when sub zero and the walls have no chance to dry out between wet weather) and also damp issues (regardless of breathable materials). I can't remember the source for this, but I remember reading that you are encouraged to use the walls as a heat sink in order to help the drying out process. Also, unless we are going to internally insulate everywhere, we'll end up with some very comfortable rooms and some very cold rooms. Insulating all rooms internally would be a huge disruption to family life, so I expect it wouldn't be something we would 'get around to' in the first year or two.

External insulation seems to be the 'right' thing to do to drastically improve the performance of a building. There are a few issues with this. The main one is altering the appearance (see Rightmove link above). It isn't the most beautiful building in the world, but we're quite keen on the natural stone as well as the foliage (although currently it needs some work cutting back and tidying up). The next issue again relates to the breathability of the walls, as we're quite nervous about getting this right in terms of using sensitive materials and preventing damp, both from inside the house and soaking up into the walls from the ground. I know that external insulation is also an expensive option with no RHI to help pay for it (and it doesn't look like many people are having much luck with the GHG either - I wouldn't be confident in finding a contractor and getting the works booked in before it expires in March next year). Also this link (https://www.engineshed.scot/building-advice/common-problems/how-to-insulate-stone-walls/#external-wall-insulation) seems to indicate that EWI might only be suitable for a harled or rendered finish, as well as the need for planning permission.

The final reason why we've invested a lot of time researching ground source/air source heat pumps is that the boiler needs replacing relatively soon. It may be an old workhorse that will continue to function, but the vendors (who have been looking after the house for nearly two years - sadly it's a probate sale) told us that the boiler is 'intermittent' despite recently being serviced with comments from the engineer that it's functioning well at the moment. It's also not a condensing boiler, so less efficient than newer models. We know that given the size and structure of the house we won't be able to heat it up in an hour or two if it's a cold evening, so we're expecting to be keeping the heating on pretty consistently over winter.

We're quite desperate not to put in another oil boiler. If we do that we know it's likely to be in there for the next 20 years or more and we have an opportunity to do a good thing and avoid burning a lot of oil. We know that either way we look at it, it isn't going to be a cheap house to heat, but a heat pump and a green electricity supplier will put our conscience to rest at least.

All this said, I'm leaning towards DJH's suggestion of getting in and acquainted with the house before doing anything significant (boiler-allowing). We have a few other priorities (levels are too high, so french drains required on the perimeter and repointing of stonework in hot lime mortar to correct previous cementicious pointing applied, as well as aformentioned loft insulation).

It is a very nice looking house plenty of character so can understand why you would not want to mess around too much with it. I note it has a poor EPC is there a requirement to have a good EPC rating for RHI ? I do not know much about HP and RHI but I know you needed a C for FIT for solar PV.

I know Carlingcott, lived in Peasedown, architected around Bath for years, and IMHO would not hesitate to EWI this house.

As you say "It isn't the most beautiful building in the world" but could become so because EWI is a great opportunity to modify elevational appearence, get rid of what's crude, improve window design/material/proportions and end up with a seriously handsome house, such as the attached (rear elevation, farmhouse nr Glasto, v beautiful Georgian front, crude Victorian rear).

Of course this is a major project, new windows, extending the eaves/verges, but after thorough insulation incl roof you'd barely need a heating system, maybe let the old boiler struggle on, for the few days it's needed, feeding a few retained rads. You woudn't need to disturb the ground floor to insulate it, if the EWI is carried down into the ground, to base of founds if modern, or as a horizontal sub-surface 'wing' if founds are shallow (or on bedrock), forming a 'coffer dam' of insulation around the ground floor perimeter. The building fabric will thrive, mould disappear, any rising damp too, with good EWI.