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Author Topic: Major house refit/extension - what should I plan in  (Read 1896 times)
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« on: October 09, 2018, 06:29:44 PM »


Extension build, including all new electrics, DHW and CH (pipework and rads with plans for UFH on about 60% of ground floor). There'll be a utility room on the ground floor with space for a gas boiler, cylinder (or heat bank), with space on the roof above for solar (heating; I think the shade is probably a bit too iffy for PV at current costs) and space outside for ASHP. There will also be a woodburner in "the snug" - the smaller living room.

I've had a spec for ASHP which, they say, will cover all my needs for CH and DHW down to -3 but... Instinct says get a backup, but I have no idea how to integrate a gas boiler with ASHP. Actually I do have ideas but the builders only think in terms of "get a Worcester Bosch combi boiler" and I haven't found an authoritative installer locally who understands the big picture, rather than tending towards whatever his specialism favours.

All I bit random I'm afraid, but that's the problem of starting with a clean sheet, so any thoughts from this group would be most welcome.

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Backache stuff!!

« Reply #1 on: October 09, 2018, 08:32:46 PM »

There is no one correct solution it all depends on how much neat and hot water you need to supply and also the lifestyle you have. A combi might not be such a bad idea for example if you can insulate like mad and don't use loads of hot water, in that case your energy demand would be so low it probably isn't worth spending quite a lot of money  on a fancy install. On the other hand if you could install a load of PV and have a high heat demand you might benefit from a heat pump (powered by the PV) and then have the heat only gasser and wood burner as back up. It's gonna be expensive to set up though so you need to consider the cost benefits carefully.

First thing to do is work out your expected heat demand and go from there.


still a crazy old duffer!
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« Reply #2 on: October 09, 2018, 11:16:12 PM »

The idea of a backup heating system makes sense and is the approach I have taken.  I took the view that a backup system should not be used that much (if at all) and that if needed the cost of running it could be relatively high since it should not be used for long. I designed our system around a therma store with connections for ASHP, WBS, ST and as backup 3 immersion heaters. Almost any boiler, heat pump or even WBS is likely to use electric power for much of the time (I assume a loading valve and pump for the WBS) and certainly the heating circuit(s) may require pumps so the immersion heaters ae a low cost backup.

For DHW I am looking at the ASHP to provide the lift in temperature from 10 to roughly 40C, and an immersion (probably on E7) to lift the relevant part of the TS from 40 to 60C. The exact top temperature is yet to be optimised.

If you have an ASHP why bother with the gas boiler at all? The GB could be an expensive solution if just for backup - even the annual service might dwarf the actual gas usage in cost terms.

Assuming you are on mains gas, have you carefully considered the cost of ASHP vs GB?

You need to look at some of the more fundamental  questions though - you may have done so but not given any information on them. How many in the house? How much heat do you need? How much DHW do you need? Have you done all you can insulation wise? How air tight is the house? Do you have a MVHR unit?
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« Reply #3 on: October 10, 2018, 07:23:37 AM »

We built an extension (kitchen/dinner, snug and master bedroom suite above) to Passive Iouse standard, so insulation sufficient that it needs virtually no heat in winter (i.e. heat comes from cooking / lighting / etc.). Because we had existing boiler we installed UFH and, hindsight, glad we did as it needs so little heat we have changed objective from "zero energy use" to "comfort".

Heating is pre-existing Biomass boiler, but I am now planning to add ASHP for both "backup" during winter, but more importantly to run it in reverse for cold-water in UFH in summer - again, comfort rather than zero-energy, and we have PV so probably no actual running costs in Summer.

The passive House extension needs something ridiculously small like 1kW at -10C, so even running an ASHP at COP=1 for the half-dozen days in the year when temperature is properly-cold won't be expensive.

I have Solar Thermal (separately for both DHW and Pool) and both have needed regular maintenance Sad - sufficient that if I was doing it again I would just do PV and ASHP; that would also give me the option to run ASHP from Grid or to use PV in house instead of heating water (not withstanding that your PV site is shaded ... Sad ). ASHP for DHW is a bit different, getting the temperature up to 60C+, rather than 40C for UFH is harder of course. Solar Thermal or PV+Immersion seems better, but both are pants in Winter (in my case I am running Biomass boiler in Winter anyway)

Things we did in case of interest for your shopping-list:

Passive House / MVHR. Absolutely Brilliant. The ducted/forced air gets everywhere, so no stagnant corners etc. Wife and I not had a single winter cough/cold since (about 5 years now), had one every year before that. House looses about 1C if we go away for 24 hours in mid winter. Hottest it got to during heatwave was 25C (hottest temp recorded in the country was 5 miles from us, 34C I think?), but as I said worth running UFH in reverse to trim that to, say, 23C.

CAT5 to every room.

Gadgets etc:

Whole-house vacuum cleaner (i.e. pipes in the wall, sockets in rooms). In use much of a muchness to a normal machine, but Dysons never used to last long for us. Only the hose to lug about, so lighter; empty the "bin" less than once / 3-months; dirty-air not recycled back into the room. Inlets under kitchen units, so can just sweep crud up to them, kick the switch and it sucks everything away.

Kitchen: Drinking water filtered tap and boiler tap (Quooker in our case, but its very expensive and (back then) we couldn't find info on whether other brands were hot enough for a good cuppa. I think Insinkerator (sp?) might pass that test now).  "Appliance garage" for all the gadgets rather than having to get them out onto counter every time. Bins for landfill, recycle and compost heap - hope council don't change the sorting requirements in future!

Larder: we built a heavily insulated cool-room (9C) with air-con type unit linked to heat-pump-thingie outside. Great for all the food when we entertain, but all drinks, vegetables etc. permanently stored in there so always cool / ready.

USB sockets.  Took me a while to find ones which were switchable, mostly they seem to have the transformers always-on - tiny Wattage no doubt, but even so ...

Lights on home automation (low voltage switches feeding to Controller which actually determines Action).  Wife and I had a long discussions about the cost of that as neither of us thought it necessary ... benefits have been:
  • single switch for Scenes in areas where we had lots of circuits (rather than rows of individual dimmer switches ...)
  • Biggest gain: ability to decide after-the-fact what each switch should do; we changed behaviour of several switches after living in it for a while
  • Some "bigger function" switches - e.g. "pathway", come in back door after dark with an arm full of dirty BBQ dishes, one switch to illuminate all the way to the sink! Ditto for from-upstairs-to-kitchen, and switches to turn everything off at night, and "spooked" switches at bedside for kids (i.e. when homesitting) if they hear a noise during the night; alarm turns on all lights in the house; all upstairs lights go off at 10AM (blinking kids!!)
  • some Vanity stuff:
    • "mood lighting" of LED strips in cupboards / table lamps; no use during summer as daylight until bedtime, but a nice surprise each 01-Oct when they start coming on just after Dusk
    • "Party" button which turns on all the appropriate lights - in the old days we used to walk around the house and turn on the light in the loo, for example ... can you imagine having to do that every time?  Grin

CCTV - including some Covert in the house (either end of corridor) to get a good snapshot of any barstewards for Plod. Friends have a "door" CCTV which has 3 or 4 additional cameras. They used it when they were away, to check when builders actually arrived onsite Smiley

"re-wire" - I would fit all essential circuits on a separate control panel, so that you can easily isolate them, then in a power cut you can limp along with non-critical things turned off - preserving Generator / battery / whatever-in-future power for as along as possible. We fitted an external "commando style" generator socket (and grid/generator isolation switch).  I have a 3kva-ish generator which cost a couple of hundred quid and we can limp along, but I expect we will have house-Battery before long.

Everything has additional isolating switches, so we turn TV / entertainment system off (at mains) when we go to bed. Washing machine etc., are under-counter in utility, but have isolate switch above counter.  I hate that all these things have parasitic power usage; and white goods notorious fire risk ... better they are off when not in use (if that is a habit you have / could acquire).

I would fit supply-cable to most suitable place for EV car charging too - dig up the drive if you need to, whilst doing all that work.  Plan [fat enough cable/duct] on all cars in the household being EV.

We didn't do Sprinkler system, but I wanted to. Couldn't find a suitable system in time before building needed to start Sad A small e.g. white-goods fire would have you out of the house for 6 months, or more, repairing the damage that smoke, and maybe fire-brigade's water, will cause.

"UFH" - dunno if you can retro fit that to the existing part of the house ... but I would if I could.  Gain all that wall space from radiators, and get rid of thermal currents in the room, improving "comfort". We have solid concrete floors, with pipework embedded in them, and highly likely that contains asbestos, so we didn't ... we would have had to move out for months for the work to be done ... but I'm sure I will regret that decision, particularly when we have to replace the existing system.
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