We moved into our current house in the spring. It's a 1960s semi-detached 4 room bungalow in Cambridgeshire, brick construction and a tile roof. Sometime in 1970s the loft was converted to add two rooms in the roof. The property has an oil boiler, electric shower and a woodburning stove in the living room. Cooker is electric. EPC was done in 2011 and is E54 – and says the area is 99m2.
There's cavity wall insulation and ~20 year old uPVC double glazing. The conversion has vertical stud walls and dormer windows facing east. I've been fitting window film to the dormer windows (the solar gain in the summer is massive). The loft floor has 100mm fibreglass insulation and 100mm fibreglass batts are behind the stud walls in the conversion. I'm guessing the ground floor is uninsulated beyond the wood flooring and carpet underlay (there's an air brick going under the floor but I don't know the floor construction). The site appears to be relatively windy, although that's hard to compare. It's unclear if the conversion flat roof is insulated - thermal camera pictures suggest it might not be.
It's been on the todo list to look at replacing the boiler, and it has now been declared unserviceable (although still working inefficiently for now). We haven't been in for a winter so we don't know what the oil consumption is like. The boiler is a 11.7-14.7kW model which appears to have been fitted with a jet hotter than 14.7kW (hence its impending demise). The radiators are mostly single-walled on conventional copper pipes (~20mm diameter).
In our previous place (a sprawling 3-bedroom bungalow, worse insulated but with solar thermal) we used 1200 litres of oil over the year, which is 12400kWh. We only ran the heating sporadically on '1 hour' mode for maybe 4-5 hours a day though.
I've been looking at ASHP but I'm a bit uncertain as to how it would work in a retrofit like ours. The RHI and GHG and our current boiler demise make this a bit more pressing than it might have been.
I'm assuming that an ASHP installation would also involve improving the loft insulation and plugging any air gaps (eg under the conversion floor). We wouldn't be able to install UFH so that would leave us with radiator upgrades I presume? We'd replace the hot water tank with a thermal store and fit a tank-fed shower. We might also look at solar thermal or solar PV (lean towards thermal because roof space is limited and it works out a bit better with RHI and GHG). We're also concerned about noise - we're going to view some ASHP installations next week to hear for ourselves.
Some questions:
Is this kind of property suitable for an ASHP, or is the insulation just not good enough? I've heard all the horror stories about undersized ASHPs in insufficiently insulated houses, but I don't know what's 'good enough'.
My wife likes to have the place cool, and likes opening windows for the fresh air. If we set the temperature to say 18C, would the system cope with the occasional window open or would that kill the efficiency? It would only be in one room at a time (except during the summer when we wouldn't run the ASHP). I don't think the house would be suitable for MVHR. We also have cats so closing doors is more difficult.
Given the 'upstairs', how do we prevent all the heat escaping into the upper rooms and downstairs being freezing? With a boiler there's a constant large heat flux into the room – I'm not sure you'd get that with low temperature rads. Obviously TRVs would reduce the output upstairs, but I'm concerned about hot air escaping upwards.
Can radiator upgrades be done by replacing single-wall with double/triple wall, ie keeping the same radiator wall area? Some can be enlarged but those below windows cannot. Others are in awkward corners, eg kitchen with limited wall space.
The woodburner is drawing in room air. Would that drive a coach and horses through our efficiency? Obviously when running it is going to emit heat, but when not running there may be some leakage (eg you leave the fire to die down overnight but it still needs air, and nobody will be there to close off the vent when it goes out). Is there any way to reduce chimney leakage (automatically?)
Would it be too taxing to run the heating at a constant cold temperature say 17C and occasionally 'boost' up to say 20C? We might boost using the woodburner, but other times we might want the ASHP to do the boost.
I have quite a bit of computing gear that emits heat (eg 400W server). This can cause overheating in the summer when there is solar gain from windows. I'm concerned that further loft insulation is likely to make this worse. Is there anything I could do to mitigate uneven heat input into the house? It would be neat if I could extract heat from these appliances into the thermal store somehow.
In the summer cooling would be very much appreciated. Assuming we fit an ASHP that supports cooling, any pitfalls? I assume I'd need to install fan coils off a separate port of the ASHP, rather than the heating loop? How does this compare with using a simple split-unit air conditioner?
Would it make sense to fit fan coils instead of rads, so they could do both heating and cooling? How would they compare size-wise? (My wife is also sensitive to noise so we might be looking at fan-off mode for heating, with the fan for cooling only).
I'm also wondering about other options. We're off the gas grid. GSHP is going to be expensive (only 150m2 of garden). Biomass seems like a lot of hassle, and space is constrained for a boiler house. A neighbour has LPG which means the front garden is dominated by an ugly LPG tank. I would quite like to recover the space used by the oil tank so moving away from oil would be handy. Wonder whether some air-to-air split units might be easier than an A2W system (although they would probably fail the noise test). Or maybe a combination of smaller ASHP plus split units?
I don't really want to get another oil boiler, but wondering how risky ASHP is...
