Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    Hello everyone,

    First post here - hoping to get some feedback on our thoughts about replacing a >30 year old oil boiler with an ASHP/GSHP in the house we're prospectively buying (a couple of weeks from exchanging).

    Firstly, a little about us - we're a young family (my wife and I and two children, 3 and 1) and although being cost efficient is important, the most important thing for us is going to be a balance of comfort and convenience. I want to try and avoid the inevitable arguments in the years to come about where to set the thermostat, which has led us to AS/GSHP because we love the idea of keeping the house at a steady temperature year round with constant heat. I've been doing a lot of research on the subject but I'm still struggling a little with viability.

    We are buying an old house which we believe the oldest part is likely to be 18th century, with 0.5m thick stone wall construction. I understand that stone walls aren't good insulators but are good heat sinks, so the last thing we want to be doing is trying to heat the house up in a hurry. It's a 5 bed detatched, approx. 180 m2. It needs more loft insulation which will be the first job when we move in (sheeps wool looking most likely) up to 300mm. The house is double glazed and although not a hugely drafty house, it's not that airtight either and we're likely to improve the ventilation.

    Doing 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, and that the peak power output required of a heating system would be c12-14kW. Using the 'rule of thumb' on this resource https://synergyboreholes.co.uk/information/calculations/ seems to indicate that more like 22kW of power output would be required in the coldest periods to maintain 20 degrees in the house. There's a massive discrepancy here and the last thing we want to do is under-spec a system. 12kW looks to be achievable for ground source or for air source.

    For a ground source system, we'd have to look at either one very deep (~200m) or two shallower (~100m) boreholes (using 35w/m of collector) which would probably be feasible, but more than two boreholes would be difficult from a logistical and cost perspective. We would prefer ground source for potentially higher COP and higher RHI payments to offset the higher cost of installation.

    For air source, there seems to be a decent amount of choice at the 12kW-14kW including Ecodan which appear to be highly rated and we wouldn't have the same space concerns.

    The property has solid floors and is slightly split level, but I've assumed we could probably fit wet underfloor heating next year to take advantage of low-temperature heat, but currently the house has decent size (but not 'oversized') radiators in all rooms.

    All this to say does anyone have experience with ground source or air source for a similar property? Can anyone offer insight on whether 12-14kW is likely to be sufficient, paired initially with radiators then subsequently with underfloor heating?

    Thanks in advance for reading this.
    • CommentAuthorrevor
    • CommentTimeOct 14th 2020
    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.
    Wot revor said +1
    I have put external wall insulation (EWI) on my stonewalled houses (2 with 50cm basalt rock and earth construction) with great success. After the insulation the effect was a lack of mould in the corners and on north facing wall and a much more comfortable living space. The EWI was 10cm thick.

    If your house is rendered then there should be no issues with planning however if you have facing stone externally then talk to the planning people.
    • CommentTimeOct 14th 2020
    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 :bigsmile: 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 :bigsmile:
    (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
    Welcome! I agree with revor - insulate, insulate, insulate (but make sure it's as air-tight as you can get it too). Edit: Agree with P-in-H and djh too, but we were typing at the same time!

    If it were me would not be taking on a house with no wall insulation (other than that inherent in the building material). If we assume that half the reason you bought it is because you like the stone (correct me if I am wrong), then suggestions that you externally insulate might go down like a lead balloon. If you have to insulate internally I would recommend a lime parge-coat (which at least in part may be the existing plaster unless it's been messed with and replaced with gypsum), then, following an interstitial condensation risk assessment, perhaps 80-100mm of rigid wood-fibre or cork on a toothed coat of lime plaster, fixed with plastic or stainless mechanical fixings and finished with lime plaster. pull back ceilings and floors so that the insulation runs seamlessly from room to room. Don't forget to parge and tape around joist ends. The recommendation re thickness should see a U value of around 0.35-ish, which is not quite on the Part L button but close enough to satisfy most BCOs in buildings like this. Only if the building is very exposed would you perhaps consider a lesser thickness.

    Breathability (water vapour permeability) is imprortant for such constructions.

    I'll leave it there for now - running out of grunt!

    And finally, don't be overwhelmed! There's loads of good help on here.
    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).
    Oh and I'm also keen to put in internal wooden shutters - the windows are double glazed but I think this will definitely make a significant difference to the feel of the rooms.
    • CommentAuthorrevor
    • CommentTimeOct 16th 2020
    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 think ther requirement for RHI is to have adequate loft insulation and cavity wall (if you can, but not a possibility here). I don't think there's any requirement for internal or external insulation.
    • CommentTimeOct 16th 2020 edited
    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.
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press