gdal Posted June 19, 2021 Share Posted June 19, 2021 We are renovating an old stone house in Oxfordshire, about 145 sq metres. Two people and two bathrooms, but unlikely that both bathrooms will be in use simultaneously. This will be a complete new system with UF heating downstairs and radiators upstairs. I don’t think we can get the house up to a level where ASHP will keep us warm enough. No mains gas, and no place to install LPG tank. There is room for an oil tank So I’m thinking a new oil fired boiler which will be inside the house. I’d like not to have to find room for a hot water tank. Does anyone have experience oil fired combi boilers such as a Worcester Greenslave ? I don’t think there are many brands that do oil combi boilers. (I must admit I have thought about putting in electric heating. I know it’s really expensive to run, but the install costs would be massively lower, so the oil fired payback time is probably at least 5 or 6 years. And by then it’s possible that electricity unit cost per Kw might be lower than oil …..) Link to comment Share on other sites More sharing options...
Temp Posted June 19, 2021 Share Posted June 19, 2021 Oil boilers aren't a great match for UFH unless you can add a buffer tank of some sort. Oil boilers don't modulate their burner, instead they turn the burner on and off to maintain the required flow temperature. This is a bit like driving a car in stop start traffic. So you might find the burner cycles on and off a lot if only one UFH loop is calling for heat. We fitted a thermal store which acts as a buffer. The store supplies the hot water for both the UFH and DHW. When the temperature in the store falls the boiler fires up and in our case runs flat out until the store is back up to temperature. The down side is that a thermal store can leak a lot of heat if not well insulated and some leave a bit to be desired in that respect. This was our first oil boiler so not sure how big aa problem the cycling issue is. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 19, 2021 Share Posted June 19, 2021 6 hours ago, gdal said: with UF heating downstairs How much insulation is going under the floor? 6 hours ago, gdal said: I don’t think we can get the house up to a level where ASHP will keep us warm enough You will if you size the ASHP correctly. 12, 18 or 25 kW is the power, this is independent of the technology used to generate it. Link to comment Share on other sites More sharing options...
PeterW Posted June 20, 2021 Share Posted June 20, 2021 13 hours ago, SteamyTea said: How much insulation is going under the floor? You will if you size the ASHP correctly. 12, 18 or 25 kW is the power, this is independent of the technology used to generate it. +1 to this. @gdal Size the rads to run at d30°C and the UFH with a small buffer or LLH and then put a slimline UVC in a cupboard and you’ll have a full electric system anyway. You need to start with the basics and a heat loss calculation first. Link to comment Share on other sites More sharing options...
gdal Posted June 24, 2021 Author Share Posted June 24, 2021 I would really like to use an ASHP but I’m concerned that given the solid stone walls, which we can’t insulate, we just won’t be warm enough. the house is currently pretty much derelict so I’m struggling to see how we can do a heat loss calculation until the renovation has been done (windows, doors replaced, new Limecrete floor). And I need to plan for the new heating before the renovation starts! Also, can an ASHP be sited away from the building itself? I don’t want to have it on the gable wall under the bedroom window, which is pretty much the only place I might get permission (listed building). Could it be say 5metres away? Link to comment Share on other sites More sharing options...
PeterW Posted June 24, 2021 Share Posted June 24, 2021 How much oil do you currently use ..? Link to comment Share on other sites More sharing options...
IanR Posted June 24, 2021 Share Posted June 24, 2021 (edited) 35 minutes ago, gdal said: Also, can an ASHP be sited away from the building itself? I don’t want to have it on the gable wall under the bedroom window, which is pretty much the only place I might get permission (listed building). Could it be say 5metres away? Yes. For a Monobloc, it's preferred to have the ASHP within 10m of the cylinder. Mine is 14m, so I uprated the insulated twin duct between the two. If you have to go significantly further apart you could consider a split system which are good for 30m between them. But this does reduce your options on ASHP you can use. Edited June 24, 2021 by IanR Link to comment Share on other sites More sharing options...
SteamyTea Posted June 24, 2021 Share Posted June 24, 2021 1 hour ago, PeterW said: How much oil do you currently use House has been uninhabited for a number of years. But knowing the power of the oil burner could be useful. 1 hour ago, gdal said: I’m concerned that given the solid stone walls, which we can’t insulate The heat loss calculation for them is easy then, and won't change. Just need to know what they are made from and how thick and air leaky. Just don't get side tracked into thinking they will 'store energy'. Just simple conductance and wall area is all that is needed. 1 hour ago, gdal said: new Limecrete floor Why? Do you like the damp. Link to comment Share on other sites More sharing options...
gdal Posted June 24, 2021 Author Share Posted June 24, 2021 I've got no current data on oil consumption, because there is currently no functioning heat supply at all. The house has been empty for a few years, and the last occupant used propane bottles and a combi boiler. There is no room for an LPG tank, no mains gas. So my options are oil (there is room for a tank) or electricity. Upstairs we have floorboards on joists, and will keep that arrangement. So that means radiators. Downstairs we will dig out the old solid floor to 300mm and install limecrete and UFH. There is a small attached outhouse, about 2 sq metres, that adjoins the kitchen, potentially the boiler room. Maybe, if I insulate this small building properly it could house both boiler and cylinder. Appreciate the input, thank you. Really I need to get a ....what heating engineer? to come and assess the specifics of the house, and advise. I'm near Abingdon, Oxfordshire, if anyone has a recommendation. Not sure if that's allowed on here, so if not apologies. Thank you Link to comment Share on other sites More sharing options...
PeterW Posted June 24, 2021 Share Posted June 24, 2021 Why limecrete..? If the floor is coming up you’re putting a DPM and insulation in to meet BRegs so limecrete is pointless Link to comment Share on other sites More sharing options...
Marvin Posted June 24, 2021 Share Posted June 24, 2021 https://www.greenspec.co.uk/building-design/limecrete-floors-for-old-buildings/ Link to comment Share on other sites More sharing options...
PeterW Posted June 24, 2021 Share Posted June 24, 2021 54 minutes ago, Marvin said: https://www.greenspec.co.uk/building-design/limecrete-floors-for-old-buildings/ yep aware of what it is, but if you’re digging up a floor to renovate then it’s irrelevant. LABC have an “approved detail” but it’s notoriously difficult to deal with and last check it was near 3 times the cost of a concrete floor. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 24, 2021 Share Posted June 24, 2021 5 hours ago, gdal said: Downstairs we will dig out the old solid floor to 300mm and install limecrete and UFH. You may want to go 100mm deeper and put 200+mm of insulation in. 5 hours ago, gdal said: what heating engineer What do you consider the minimum qualification is for an 'engineer'? Link to comment Share on other sites More sharing options...
gdal Posted June 24, 2021 Author Share Posted June 24, 2021 The walls are solid stone and rubble with no DPC. I believe that putting down a concrete floor with an impermeable membrane will potentially cause problems as moisture in the soil will migrate to the edges of the slab and into the walls. So breathable structure is advised. I can’t go deeper than 300mm Link to comment Share on other sites More sharing options...
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