JohnMo

If the losses are that high would you be better installing 22mm pipe, have high velocity and install a return pump to overcome the pressure loss. The return pump would pull about 33W - set to fixed speed so the heat pump variable speed pump can do its own thing.

You really need to have a manifold to run the UFH and mixer, not run from same circuit as radiators as the flow temp required will be very different. With UFH you need plenty of insulation beneath it, (150mm PIR ideally or more of other insulation materials) otherwise you will spend most of your money heating the ground, not your house. Are planning for this activity? There are good benefits with UFH in a well insulated house, as flow temps can low. In a not well insulated house flow temps can be higher than oversized radiators. If your flowing 55 degrees now, a slight upping of radiator sizing in the main living space is all you need to do for a heat pump. You may be better doing that, make the radiators ok for an ASHP and reap the benefit of low flow temps on your gas boiler and have it setup to weather compensation. Love UFH but it's not right everywhere and every house.

Just to complete this thread off. Continued to get reduced gas consumption, until the heating went off in April, with the previous mods made and a slightly changed operating mode. The heat meter installed showing circa 108 to 110% boiler efficiency. Weather compensation, proved to work well when it was cold (3-4 degs or below OAT), but less effective as it became warmer using more gas than expected. So moved to a weather compensated UFH batch charge. Set a WC curve that required approx 7 hours to charge the floor and used a 0.1 hysteresis timer/thermostat to control when the heating started and stopped. Approx. start time was midnight and end time 7am. If there had been solar gain during the day the thermostat would be later starting the UFH, if the curve was out, the thermostat would catch it either allowing over or under run times, so switch the heating off sooner or later than 7am. Things I found when setting up and monitoring Low flow temp and gas boiler gives a big jump in boiler efficiency - from low 90s running at 50 deg to over a 100% in the low 30s. UFH manifold mixers always mix return and incoming flow, so to flow 30 degs in the UFH loop you need to provide around 34 degs at the inlet of the mixer. And to get that close required lots of balancing of the flow screws within the mixer. Gas boilers can be problematic in low energy houses, either requiring a huge buffer or a small boiler with lots of turn down. Next Have now installed an ASHP (eBay bargain) used plenty of the lessons learned from experimentation, plus I wanted some summer cooling. My original UFH setup had a boiler pump, buffer pump and UFH pump, with 2 of the pumps running 24/7 during heating season. Using approx 260kWh of electric (£90 at todays cost). This has been reduced to ASHP circulation pump only, which only runs when there is a demand for heat. Now only have one thermostat, that can do either heating or cooling. No actuators on the manifold. Have also connected UFH to summer house that will be used all year round. UFH has no mixer or pump, run direct from ASHP (both house and summer house). Used a mix of 28mm, 22mm and 15mm Hep2O and copper to connect everything up. One issue was connecting the DHW cylinder, as I reused the original boiler to UFH pipes in 22mm. The long pipe run gave a pressure drop issue. To resolve I added an additional pump used only for DHW heating in the return line from the cylinder. This pump only runs would the 3 way valve is energised for DHW heating, so runs less than an hour a day. Can now do UFH cooling. Currently running floor cooling when house is above 20.5 degs, basically running off PV, generally runs 8am to 5pm, with a while off when DHW occurs at 9am. Flow temp set to 12 degs though UFH loops, no buffer on a single zone, 6kW ASHP has been set to run minimum Hz, almost whisper quiet and runs for approx 20 mins at a time, so only 2 to 3 cycles per hour. EER (CoP for cooling) is around 5.5 to 7, so pulls about 1kW or less from the solar PV available. Heating will have to wait to Oct to see what I need to setup, preliminary WC curve setup..

How do you heat the house?

Is that a summer house in the back garden, what about next to that?

Mine is 400mm, if it was that far from the wall, maybe that position isn't the best, as most of the path would disappear.

Box pipes in add plenty of insulation, paint white will not see them, cheaper than UV resistant insulation. Looks better, are you far enough from the wall to meet the minimum distance requirements stated in the manual?

Just need a plumber who isn't short of a brain cell or two. You need either a 3 port diverter (not a mid point valve) to suit the piping size you have, or an alternative is 2 off, 2 port valves, one normally open the other normally closed. The normally open one is used on the central heating side the other on the cylinder side. You should have a power signal coming from ASHP that gives power the diverter valve when you have a call for cylinder heat.

Don't you need planning permission to site at front of house? Not sure that location is classed as permitted development. I agree with her it looks rubbish.

Why? Standing charge is small compared to usage. It's the price difference between day and night and standing charges on E7 and that compared to standard rate electric with its standing charge.

Just had a look on money saving expert and they did a writeup on the benefits or otherwise of E7. Unless you are using a min 40% of your all electric on cheap rate, you are loosing money by having E7. https://www.moneysavingexpert.com/utilities/economy-7/

Is this a new build or refurbishment?

I started and paid to install 6 zones, not knowing much better at the time. All hard wired to an UFH wiring centre. None are now used, were just a waste of time and money, really not good enough for UFH. Now have a single 0.1 deg hysterisis wireless thermostat controlling an ASHP directly for overheat protection. UFH wiring centre not used anymore, as UFH manifold is directly pumped from ASHP also. keep it simple.

The install and supply needs to be the same company on the same invoice to be zero vat.

No problem. Makes a bit more sense than the MCS guide.

The attached tells you how to work out the sizing of you radiators. HPAI Heat Pump Code of Practice.pdf

Do you need a split at all? Certainly on option 1, a monobloc could do that service. Saves the complication of refrigeration engineers. For your info I'm running a monobloc about 12m from my UFH manifold and another 8m to the hot water cylinder. Everything runs on the ASHP package circulation pump, except cylinder heating where I have a boost pump in the return line, pulling 33W only when cylinder heating is active. Bigger impact to option 1 or 2 maybe the balance of the rest of the system in house.

If you have a momentary switch as suggested above, super simple cheap as chips. Switches couple of pound, two core cable of any size will do. We have them on all wet rooms, first months we used them, now almost never. And that's with the MVHR turned down considerably from initial commissioning settings.

Not sure I could agree. If its 30 outside for day/weeks on end, as soon as you open a window or door or get any solar gain, your house will start getting warmer. You house will get hot. An ASHP that can do cooling is zero cost investment if you are having an ASHP anyway, if you have UFH all you need is a thermostat that can do heating and cooling control. We had -9 for about three days last winter (24/7), then several days where the temperature never got above zero. We needed plenty of heating. I sure most house would.

Good post, to add at congested area you may need to insulate the UFH supply pipes to avoid general room overheating also. Another advantage of a thick screed is you use it as a thermal store, so if your boiler or heat pump is too big in the shoulder seasons, you charge the floor at a hotter temp than would be normally ideal, for a few hours and it will drip feed the house with heat for the rest of the day; like a storage heater.

I have noticed from conversation here and looking at MCS calculation sheet, is they make no allowance for MVHR, so will always provide an oversized heat pump for low energy houses. You may be better sizing yourself with assistance on here. Buy and free issue to plumber to install or do it yourself. I pre ran all our cables terminating everything except the fuse box. The electrician ran through everything and did final connections, cost about £200. Materials for our install excluding cylinder and heat pump, were about £1500, but that included a long external run and all insulation. Your blocks could leak quite a bit without the plaster sealing the surface.

Basically yes But using your example of airtightness from 6 to 1.8 would also mandate MVHR on a new build, so that would be a dramatic decrease, you come down a size or two on heat pump. If you are trying for 6, you aren't trying anyway, so not likely to be taking airtightness measures. You are going to have 100mm dia holes in every wet room for the fans, so reality you will leak air anyway. Running cost could be higher, buffer sizing may also increase, with an oversized heat pump. But you wouldn't do the final spec on heat pump until you know what your the most likely heat needs are. Would be better to specify after an initial air test, which would be prior to plasterboard. Over specced UFH doesn't matter, cylinder will be the same

I would split the tasks to different people, UFH and DHW could be your local plumber, heat pump most likely not your local plumber, without some assistance I e. The the design already done. But it's all quite straightforward broken down to piece parts. DHW is just UVC with 3m2 heating coil. Size will depend on house size number of occupance. UFH heating pipe layout will depend on single floor or multiple levels, heat losses upwards and downwards. But once these are known quite straightforward. ASHP really depends on heating demand, need for a buffer will depend on number of zones you break you UFH into. One zone likely no buffer required. Any more than that a buffer likely to be needed. A buffer can kill efficiency if you are not very careful with its design. Then all you really need is a 3 way diverter valve. And size the piping. Going to one company and taking the grant, will be expensive.

Seen the idea on another forum also. If the heat was coming from somewhere else other than the heat pump, that may work. Such as from solar thermal. If the heat, to heat radiator came from the heat pump, you would have to make more kW out of the heat pump to support the radiator. So the result would be likely be more energy usage, not less. You can't magic energy or efficiency from the same heat source. Have been mulling the idea of a radiator heated by solar thermal, heating the air being pulled in by the ASHP fan. Issues I have thought about, would need to run a small pump to circulate through solar panel and some control logic. Weather compensation would require temperature probe moving as it would be influenced by radiator heat. Days where it would work best are, cold sunny winter days and if you tied in the logic to work with DHW heating all year. But would need to be off when in cooling mode. Have everything needed in the garage, may be worth rigging up if I have a day spare.

Plenty near us, 12 months later the slates look perfect, the tiles have started to get yellow moss, algea all over them.