So, Every now and again I look at replacing my direct electric heating with one or more heat pumps. This time I've got slightly different answers that I don't fully understand and could use some help with.

I presently heat my house with an electrical post-heater in the MVHR duct (nominal 1.8 kW), plus a radiant heater by the front door (also 1.8 kW). Both are operated only at night as required, unless there are truly exceptional conditions. Hot water is provided from a thermal store that is heated by PV when available and backed up by a 3 kW mains immersion, again operated for a few hours overnight, when necessary.

I've looked at A2A heat pumps as being simplest and cheapest. I don't have any wet heating circuits. I thought about putting in just one indoor unit in the living room. But now I'm thinking that the MVHR post heater works by heating the air to 45°C and circulating it. I wonder if a single heat pump emitter can do that job? The front door heater is on the north side of the house and in an open lobby so it manages to heat up the colder part of the house a bit extra when necessary. How would I determine what I need?

I've also become aware of heat pump water heaters recently, so I've considered getting one. But the ones I've looked at seem to have the heat pump packed along with the tank and so have massive great air ducts to/from the tank. I don't fancy cutting big holes in my walls. The ones I've seen are also cylinders rather than thermal stores, so need annual inspections and more maintenance. Are there any products that provide the benefits without the costs and hassle?

I also happened to look at the boiler upgrade scheme - https://www.gov.uk/apply-boiler-upgrade-scheme - and was surprised to see that the eligibility conditions appear to include me. It says "replacing fossil fuel heating systems (such as oil, gas or electric)". Well my system is electric, so am I eligible? Does anybody know, before I "speak to an MCS certified installer"?

Posted By: WillInAberdeenWhat would you aim to achieve, given your current setup and consumption?

Good question. That's one reason why I haven't done anything yet. Assuage a vague feeling of guilt?

Reduced lifecycle costs? (unlikely)
Reduced lifecycle carbon? (fairly unlikely)

As you say, they seem unlikely.

You likely already found that 45⁰C is a bit too hot for an a-a, and your daily heat requirements are too low for most a-w (~10kWh daily?)

Yes to both, although I don't see any reason in principle why an A2A shouldn't heat to the same temperature as an A2W. Heat pumps are becoming more common in cars nowadays, so there's another wilde idea.

You could fit a very small a-a, heating the MHRV duct to 25-30⁰, so a power of a few hundred W, run it for more hours each day to get enough kWh out in total?

I'm still not clear how I would heat the duct. It would seem to involve a bunch of custom metalwork to adapt a rectangular heat pump emitter to my circular duct. And extra space in the plant room, which may or may not be a problem. At the moment I'm on an E7 tariff and switching to an equivalent all-day tariff would cause a significant increase in price.

Could you heat the duct using water from the TS? Also pump the TS water through the wall to/from a location suitable for an a-w and heat exchanger, if you can find one small enough?

The TS is near an external wall, so putting small pipes (gas or water) through the wall could be a necessary evil. But the TS is the opposite end of the house from the plant room with the MVHR, so that would be awkward.

Wouldn't bother with MCS, they have to follow a particular accredited process, which will be overkill for your house.

Yeah; I'll probably try one and get frustrated and then try to find a good one who isn't MCS, which I suspect is more difficult. But I might learn something from the MCS one.

Posted By: neelpeelPossibly not. I'm on E7 (charge EV overnight) but looking to switch to the Octopus Tracker tariff. Worth doing the sums...

That requires a smart meter, which I presently have religious objection to. (no local access to my own consumption data, despite a legal obligation to provide it AIUI).

But if I overcame my objections, is there a site somewhere, or a program to download, where I could put in my consumption history and see what it would have cost on the Tracker tariff? (and yes it would be an approximation since I could have moved consumption around a bit but you have to start somewhere). Looking at the graph in your link, it looks like it would have been more expensive during December for example. And everytime is more expensive than the night rate apart from a short time on 29 Dec.

Posted By: djhno local access to my own consumption data, despite a legal obligation to provide it AIUI).

Octopus give access to download all your consumption data and do with it as you please. Here is a snippet from a .csv file from my yesterdays usage...

0.158 2023-02-01T10:00:00+00:00 2023-02-01T10:30:00+00:00
0.096 2023-02-01T10:30:00+00:00 2023-02-01T11:00:00+00:00
0.132 2023-02-01T11:00:00+00:00 2023-02-01T11:30:00+00:00
0.132 2023-02-01T11:30:00+00:00 2023-02-01T12:00:00+00:00
0.118 2023-02-01T12:00:00+00:00 2023-02-01T12:30:00+00:00
0.311 2023-02-01T12:30:00+00:00 2023-02-01T13:00:00+00:00

Not sure about working out the historical Tracker costs. I just did a rough estimate based on the graph and last year's average and looked like I would be quid's in.

This guy archives all the price data every day for each Octopus tariff and you can graph it or download it to compare with your historic consumption however you like:

https://www.energy-stats.uk/dashboards/

There's probably an app to do it all for you, there are people hanging around the OEM forum who are good at that sort of thing.


BUT you care about future prices, not historic prices. There's a lot of talk that energy prices will be lower this year than last. The energy companies all hedged (prepurchased) energy at last year's prices, so are now paying more than the market rate, which is why Tracker and Agile are cheaper than the fixed tariffs at the moment. That could change at short notice of course. Do you want the certainty of a fixed price (paying extra for the certainty). If Tracker or Agile doesn't work out for you, you can switch back at short notice so the risk is fairly low, but I have learned not to believe financial advice (including this post!)

Think you can access their Tracker tariff without a smart meter, it doesn't change quite as frequently as their Agile tariff.

They also have tariffs aimed at heatpump or EV owners with various cheap periods in the afternoon or overnight.

That was my point -
If you compare with a period including the sky-high prices of last August, then a variable tariff will look expensive.
If you compare with the month around Christmas then a variable tariff will look cheap (average of cheapest 4 hours each day on Agile = 12.6p).

Both of those are meaningless comparisons, unless you have inside knowledge that future prices are going to be more like August, or more like Christmas.

The Bank of England announced today that they expect energy prices to trend down, but they're guessing the same as everyone else.

Most of us don't have bandwidth to stay on top of this, which is one reason why take-up of ToU tariffs has been slow.

(Edit to add: their EV tariff is 12p overnight and 43p the rest of the day)

When you say assuage a vague feeling of guilt, is it about your remaining heat carbon footprint? If so, as Will suggests, if that footprint is already low, then aren't you stuck because the embedded carbon in any solution you adopt might exceed the savings (or near to it)?

It's a problem for anyone who has already 'walked the walk' to the extent practicable.

My own sense is that in this case you might consider offsetting your remaining emissions. There are all kinds of criticisms of offsetting, but they all boil down to the need to do far more of it than calculations suggest.

We offset three times our entire household's entire carbon emissions, and our house is an energy monster, for the measly sum of £37 per month, because carbon offsetting is cheap. It's probably already nearer four times, but I'll probably up it to five, as then I can be absolutely sure I'm at least offsetting our emissions (given deficiencies in offsetting).

As it's nearly impossible to reduce a household's emissions to a truly sustainable level in the UK, and we have to think about our historic emissions, I do think this has a role to play.

Thanks. Hmm, do you have any idea what it means when I get the following when I start the app:

EmonCMS Error
-------------
Message: ReferenceError: path is not defined
URL: http://emonpi/emoncms/Modules/app/Lib/feed.js?v=
Line: 33
Column: 13

The solar generation app works OK so it's something specific to this app. Where and what is the 'path' variable set?

An idea for the OP if they’re still looking for one..

1) use a Sanden CO2 hot water heat pump. This heats a *large* cylinder up to 60 deg C or more, using a small outdoor unit. It has a “towel rail” takeoff coil. Use this for your duct heater. It obviously also does your hot water. Charge it at night on the cheap tariff.

2) if the above isn’t available, you can achieve the same thing with a conventional ducted air source cylinder, LG sell a good one. In this case I would suggest using one for your duct and a second one for your hot water. They’re not crazy expensive though. Again, charge off peak as much as possible. Batteries can help time shift the heating load too.