Energy useage/cost for average 1930s 3 bed semi?

It's likely to be 90% natural gas and a 10% hydrogen (maybe 80/20%) mix at best and not the misleading 100% hydrogen green hype.

Firstly, no, they shoudlnt be higher. Read the original post. It is a hybrid system, with an ASHP and a gas boiler. The gas boiler takes over the HW/CH when the temperature falls below a certian outdoor temperature, usually 5 or degrees C., the point where the efficiency of the ASHP drops to belwo that of the gas boiler. This system should be more efficient than a single gas boiler, or a single ASHP, as the system uses the cheapest item to do the heating as and when necessary. If it is integrated to the solar output, then it should be a lot more efficient, and cheaper than a gas boiler alone.

Even with just an ASHP, the total energy bills should be less than with a gas boiler, as the house now has solar panels, and even the worst ASHP on the market can achieve a COP of 3.5, add in the solar, and the bills should be a lot less than the combined electric and gas bills were before the upgrade.

Unfortunately, they arent. That is the tested figure, in ideal conditions, with a new boiler. Once cycling of an oversized boiler is taken into account (90%+ of UK boilers are oversized), most boilers struggle to get to 90%. Newer modulating boilers help, and bring up efficincy gains, but unless the system is designed for that boiler, they will never reach the claimed efficieny figures quoted by the Manufacturers.

With electricity several times more expensive than gas and solar panels being pointless in winter, heat pumps are way more expensive than gas even in a building that is insulated to the nines.

Even when you do, it turns out worse. Or so my friend who bought an up to date eco-house told me.

Until we have nuclear electricity a heat pump inst worth it, and when we have nuclear electricity we wont need a heat pump anyway.

ITYM close in money terms, not in kWh terms? Our pre-ASHP EPC (for what it's worth) says heating would have needed 11200kWh pa, and 2700kWh pa for hot water. We've achieved less than that over 4 winters, making the SCOP roughly 4.7 (an overestimate, as there's from now until December to make it a full 4 years, but heating demand until then is likely to be limited apart from maybe November)

Indeed. A big chunk of that is covered by the Boiler Upgrade Scheme grant nowadays. Makes it roughly comparable with a gas boiler replacement, or cheaper in some cases.

Theo

As posted up thread, the hybrid system seems to be aimed at minimal installation cost. No new plumbing and larger radiators. No hot water storage. So basically keep your existing system but add an additional heat source to the mix (and tick a green credentials box). The ASHP is (as far as I can see) equivalent to base load with gas used to top up any heating demand above the capabilities of the ASHP and to provide hot water.

I am not convinced of any major benefits beyond improving your carbon footprint.

Cheers

Dave R

Not in my experience. I got quotes around £15000 for the ASHP/HW cylinder, making my contribution after the grant £7500.

A decent gas boiler replacement < £3000.

I suspect that isn't going to work very well. The ASHP wants to run at low flow temps, ideally ~35C. A traditional boiler system is designed to run at

If you upgrade the radiators for the heat pump then the boiler can run at a much lower flow temp (=more efficient), but you need a condensing boiler for that. If the boiler is old enough that people are thinking of upgrading, then possibly it's too old to condense (very much) or do weather compensation. Also, as a combi, you need a very wide range of modulation - because the combi will be sized for 30kW of hot water and not 1.5kW of heating load.

If you don't do it right I think it's going to work out worse than one or the other. You can't just slap in an ASHP on an existing combi system and hope it to be efficient. Maybe there is a place for a combined system, but both parts need to be designed to work together.

Now, if you installed air to air units (ie air conditioners that can do heating) and kept the combi for the hot water only, then I could see some advantages.

But if you are going to have an air2water system it's disadvantageous not to have it do hot water too. I would be looking very hard for somewhere you can put hot water storage - especially if you live in a house, where there's more space than a flat.

Theo

The basic config allows the ASHP to signal the boiler to turn on when the outside temperature reaches a low set point, this varies by Make, typically 5 degrees or so, just when the COP of the HP is going to take a hit, so it is cheaper at that point to use the gas boiler.

A truly smart system can be fitted that will automatically allow whatever energy source is the cheapest at that time to be used, for example, the temperature may be 2 degrees outside, but a cheap rate of electric is available, so the system uses the HP at that time as it is the cheapest way of heating, even if the COP is only 2.5 at that outside temperature. Solar can be integrated into the system too.

My gas boiler replacement cost just around £3000 and that included moving it to a new location and removing and disposal of redundant pipework.

I read recently that the average cost of installing an ASHP from Octopus was in the region of £11k (incl the £7.5k grant).

But can you get a £7.5k grant (or other social grant) for such a system?

And why a heat pump *and* a gas boiler. This sounds a bit odd. Are we sure it isn't some sort of heat recovery system to reduce condensation ?

But little or no gas is lost between Milford Haven or Norway and the end user (and if any was Thansco would be on the case PDQ), whereas quite a lot of electricity is 'lost' between generator and end-user because of heat etc

OTOH, the residual heat from the gas boiler is within the thermal envelope, whereas the heat from the outside compressor and fan motor of a heat pump, really is lost to the outside air.

By the time it gets to the end-user, it will be closer to 100% natural gas, unless they replace all the nations underground pipework. There are millions of houses that still have bits of 3/4 screwed iron and those pesky H2 molecules are just going to whizz out of the joints.

Blimey, I use about 3000 KwH per year and for a about 20 years since I ripped out the Baxi Bermuda back boiler and most of the pipework (don't ask!), that includes minimal heating, and only one room properly warm in winter.

I have 300mm of insulation in the loft, the front (North) wall has 80mm of celotext on the inside downstairs from slab up to ceiling + PB. I dug out the screed of the solid ground floor in 2011 and laid another 1200 gauge DP plus 3x2 battens vertically set, concrete screwed into the slab with 250mm gaps infilled with

Most of my heat loss is through the gable end (east), via the brick+65mm rockwill-filled cavity+inner block, and old aluminium DG patio doors and a couple of original Boulton and Paul single glazed timber windows.

The party wall is a cavity wall and there is still some air- leakage through that (it was awful back in 1992), but now both semis have cavity wall insulation that has been massively reduced.

At the moment I am using about 5 kwH /day, sometimes down to 3 if I am out and about and the weather is warm. Watching YouTube or using the computer much of the day pushes it up a bit.

I have a 37 degree pitch due-south-facing roof so solar PV and a battery system would 'work' for me, but I don't have an EV so the cost/benefit equation is tricky.

The big problem with heat pumps is the need to have quite a lot of space for the internal pressure vessels and pumps etc, over and over the HWC. I have the latter, but where did you put all the other gubbins in your bungalow ?

Andrew

OK, if I'm reading that correctly, makes the decision to go ASHP much more attractive - roughly equivalent to gas boiler replacement.

I enquired about a year ago, the shortage of installers meant prices were inflated, and the grants were pretty much universal. The move will be towards an element of means testing I feel. But for now, I think pretty much anyone can get the grant.

Might be easier to have an air-to-air heat pump, and avoid any plumbing changes. Add solar PV and a battery and you have cheap/free air con in summer and in winter use the overnight tariffs to charge the battery or run the heat pump.

Well a full passive house, there should be so much insulation that even storage rads might be all you need.