MortarThePoint

Sounds great. That's the unit I'm considering, but I'm tossing up between 3phase and single phase. 3phase is £500 extra. Programming the controller scheme or were there other aspects to look out for?

What model ASHP do you have?

Just spoke to someone at Scheidel and the spigot on the adapter is 100mm long anticipating the flue pipe being cut short to allow it to be slid up allowing stove to be slid under. That should make it easier. I confirmed that no sealing is then required at that junction, so it will be allowing expansion. I didn't ask, but that would make it important to hold the adapter in place as could fall down otherwise opening a big gap. The technical guy said that no rope or cement is needed with the adapter as it already has a rope tape inside. @joe90 your setup sounds more belt and braces and clearly works well. I think I'll follow the recipe of the phone call though as my stack up is: Stove 5-6VIT vitreous adapter to mate 6" pipe to 5" stove outlet 6" vitreous which I need to cut to size Isokern adapter 6" to 175mm Isokern support block I've bought some 3mm aluminium sheet cut to size (2 halves) to make a plate to go around the pipe. I still need to cut the pipe hole (semi circle in each half of the plate) which is unfortunately going to coincide with the pipe's door, but can't be helped.

Where did you allow for expansion? You have glued the adapter to the pumice, did you need to pack it with any fire rope? What glue did you use or was it just 'fire cement'?

What did you go for in the end. I'm at 11.2kW so a little lower, but a 3phase is quoted to cost £500 more than the single phase of the same model. Like you, I will have 3 phase power either way.

Fair enough, but we are in odd times and am I going to be able to get a new tariff like that (i.e new customers)? Personally, I can't have grid gas anyway so the toss up is vs oil for me which is around 90p/l -> 90p / (10.35kWh/litre * 85%) = 10p/kWh of heat Assuming an oil boiler efficiency of 85%, I need an SCOP of 2.9 or higher presuming I can get the 34p/kWh electricity tariff.

I don't understand the 'is an ASHP cheaper to run' problem if using it with UFH on the correct centres. If there was a large non-linearity in it's output (i.e non-flat efficiency curve) then it would make sense. Unless you need power past the tipping point, the problem can be overcome by duty cycling can't it. ASHP plus radiators, that's a different matter. Without savings associated with E7, ASHP has been and will be* more expensive to run than grid gas for all houses won't it. [* for a while at least] Is it worth installing, that's harder to understand as you need to offset the capital cost.

I'm surprised your indoor temperature is so constant during the day without the heating on. Do you have lots of glass and solar gain? It starts to drop at 9pm at a rate of around 1C in 5 hours.

Interesting. I think taken over such a long time the effects of solar gain mask the most interesting bit. Do you have that for just January 2022?

Do you have a graph of indoor and outdoor air temperature vs hours of the day? I'd be interested by the dT/dt when it's cold outside.

I used gas generated for my comparison in the first post (just pointing out coal would be worse). I need to consider marginal as I am deciding whether to add one extra system, not form a government guideline

Are the powers the power taken from the grid or the power consumed in the house, or do you not have batteries?

That agrees reasonably well with my estimate: ASHP: When heating using an ASHP the marginal electricity* will be most likely generated from gas: 0.5kgCO2/kWh electricity / 300% = 167gCO2/kWh of heat But if the marginally electricity is coal generated....

Two counters to that: Are you sure no gas derived electricity is generated overnight? If there is sufficient hydro storage, the electricity could be stored and used later, may not be enough capacity though Additionally, if but not connected to E7, some people charge their cars outside E7 e.g. during their day at work.

I agree, electric cars etc will create larger overnight demands. This is a key point that is so often missed in the consideration of electric cars. If you're weighing up the choice of something that uses electricity Vs something that doesn't, you need to model it as additional demand on the grid. Some made up numbers to illustrate: Scenario 1: 2.5GW of green electricity, 0.5GW of dirty electricity, my oil heating. Scenario 2: 2.5GW of green electricity, (0.5GW+3kW) of dirty electricity to include my ASHP. The green electricity can't be dialed up to match the additional demand. Until we have excess green electricity capacity that is, which is a long way off. ASHPs and Electric cars will see us burning natural gas for years to come. Without them less gas would be burned, so their carbon footprint is that of the extra gas that is burnt, not the average electricity generation footprint.

I don't know how mass adoption of ASHP will come about until the running cost is comparable to oil/gas heating. The grants address the increased capital expense, but not the increased running cost. Electric cars may limit the lifetime of E7, I don't know, but that isn't a solution for existing building stock anyway. It will be very unpopular to tax oil/gas heating out of existence. I also find it hard to imagine a running cost grant for ASHP or disproportionately lower electricity prices.

I'm not on a tariff yet so it will be whatever is available as a new customer which doesn't look great

Are Octopus allowing new customers on that tariff?

That's the marginal figure based on natural gas generated electricity. Need to consider the marginal figure for this comparison as all green electricity already being used.

I'm not too worried about the blackout prospect, but the ability to buy you energy when it's cheaper is a huge plus for Oil. A generator would cost a fortune to run surely.

I have been planning to use an ASHP so have pipes at the required 150mm centres. Given the energy situation, I am now less sold on an ASHP vs Oil. If you have a tank full of oil you know you can heat the house, not so it there is a risk of blackouts. We'll have log burners as well but that's obviously faff. Environmental: ASHP: When heating using an ASHP the marginal electricity* will be most likely generated from gas: 0.5kgCO2/kWh electricity / 300% = 167gCO2/kWh of heat Oil heating: 2.52kgCO2/lire / (10.35kWh/litre * 85%) = 286gCO2/kWh of heat Winner: ASHP 42% lower* Cost Install: Hard to say accurately but about the same given the grants available. Winner: Tie Cost to run: ASHP: Assuming 300% efficiency again and current electricity price of 45p/kWh -> 45p/kWh / 300% = 15p/kWh of heat Oil: Assuming 85% efficiency again and current oil prices of 90p/litre -> 90p / (10.35kWh/litre * 85%) = 10p/kWh of heat Winner: Oil 33% lower Personal Energy Security: ASHP: heat demand is at a time of year when personal generation not really viable so dependent on supply. Supply could be subject to interruption (blackouts, smart meter bugs). No flexibility on price. Oil: bar it being stolen, when you have it you have it. Can stock up when price is low. Winner: Oil [Interestingly, for gas, the environmental is much closer 185gCO2/kwh (so ASHP saves just 10%) but running cost even lower though grid supply so security not so good] * Using marginal generation figure as I am weighing up adding an additional electricity load, rather than the average. The longest streak without coal is 67 days, so perhaps should use coal for this calculation: 0.8kgCO2/kWh electricity / 300% = 267gCO2/kWh of heat ASHP 7% lower than Oil That 67 days is unlikely to be over winter. Government plans to ban coal powered generation towards the end of 2024, but that may get pushed back. I doubt these figures include full CO2 emissions from transport, infrastructure, workforce etc.

The second scenario also assumes you can set at TMV as low as 30C.

About £60 of parts and labour, so not much. That would be paid back in about in about 3 years. It feels quite 'sensible' from a fast hot water angle though. Cheaper and probably less heat inefficient that a circulating hot water supply to the tap.

Is this a crazy idea? I could have a single pipe going to the cloakroom served by a TMV back near the cylinder. It would mean that the water is already warm when it comes to hand washing. And requires only one pipe to be run. Energy would only be wasted in non-heating months and by the lower efficiency associated with hot water from ASHP. Perhaps 3L*50C*1Wh/200%=0.08kWh (=1.5p) per flush in summer and miniscule in winter. 2*4*1.5p=12p/day for family of 4. An alternative is to have a TMV in the cloakroom set to about 30C and pure 'hot' would run until genuinely hot water arrived. This would get rid of the cold water in the hot pipe when the toilet starts filling which is probably long enough before hand washing starts. Energy cost even lower. Would any regs rule this out?

Each room is going to be isolatable back at a manifold in the plant room, so I am not planning to have isolators at basins etc. Does that sound sensible?