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

Is that a disguised loan repayment for the 'free' system?

switching from a gas fired heating & hot water system to an air source heat pump actually worsens your EPC rating and as electricity is almost

As far as I know there are no concealed repayments. I did ask the question, having a nasty suspicious mind.

At the moment just trying to establish an expected baseline cost for a gas central heating house.

Cheers

Dave R

You're not allowing anything for the CoP of the heatpump?

I am intrigued by the hybrid system of a gas boiler and an air source heat pump.

There must (should?) be some fancy footwork to decide what to use.

In the absence of battery storage (which there isn't) I would assume that the gas would be used any time the solar panels were not generating enough to drive the ASHP. However I sometimes take a simplistic view.

Cheers

Dave R

PV is unlikely to ever generate enough to run an ASHP, assuming a not brilliantly insulated 30's semi, that could require a 10kW unit, so the PV will just offset some of the electricity costs over the year, and sell some unused power back to the grid.

So it seems sensible to use the ASHP when electricity is being generated to partially offset the cost, and use the gas when there is no electricity being generated.

Else why the hybrid system?

Unless the ASHP is run using off peak electricity and the gas is used to top up.

Cheers

Dave R

All sorts is possible, you may have a lot of homework to do ...

That is my first homework assignment.

Apparently you can install an ASHP without any major modifications if you also have a combi to handle the difficult stuff.

No larger radiators, not hot water store.

Just use the ASHP as background heating and use the combi boiler for hot water and topping up the central heating when the ASHP can't cope.

Smack of greenwashing to me.

Cheers

Dave R

Consumption since 1 Dec 2021:

ASHP only: 11322.86kWh Immersion heater (legionella cycle plus occasional free power from Octopus):

Works out to be 11754.66kWh.

Let's say the price cap is 25p/kWh.

Total cost for heat over ~4 winters = £2938.67 at current rates. Average monthly cost for heat and hot water = £71

If we take the winter to be 3 months and assume minimal heat the rest of the year (ie ignoring hot water and spring/autumn heat), works out to be £244 for the winter months.

I would guess somebody is looking at the peak winter consumption and panicking, without realising that you don't need very much heat the rest of the year.

My recent billed consumption for each month end (bill date is mid-month, ie 'Sep 24' is ~15 Sep to 15 Oct) have been:

Apr 24: £117 May 24: £100 Jun 24: £89 Jul 24: £92 Aug 24: £91 Sep 24: £103 Oct 24: £138 Nov 24: £215 Dec 24: £269 Jan 25: £293 Feb 25: £221

(in Mar 24 and Mar 25 they did some complicated billing recalculation and I can't see the cost at a glance. But guess it'll be somewhere between Feb and Apr)

This includes all the other electrical stuff like computers, not just heating.

The hybrid gas thing is a worrying point for me. If you live in a farmhouse or a mansion then keeping gas may make sense, but otherwise it's just needless complexity. If they don't have space for a hot water cylinder and kept their combi boiler then I suppose that might be a reason.

(you can find a lot of places for a hot water cylinder nowadays, including in the eaves space in a loft conversion or in kitchen cupboards, so I think even that's a mark of not trying hard enough)

When was the system installed? Was it during the winter by any chance? In which case not surprising it's going to take more when it's cold. Did they happen to get a smart meter at the same time?

If you don't pay attention to your meters then it's easy to average out the coldest part of the winter with the mild autumn and not realise that consumption spikes on freezing days. A clear day when it's below zero can take a lot more than the next day when it's cloudy and 5C. It just depends on run of the winter how many of each you get - but it will be a mix. Overall, the mild days tend to outweigh the freezing ones.

Theo

Is that £350 just for the coldest winter months or for all months?

I don't that there any grants for a hybrid ASHP+Gas for central heating. Why would a properly designed ASHP need additional gas heating in a 3 bed semi?

Or that a gas boiler may be running at 80%. or less, efficiency.

That's fairly close to our annual gas consumption for heating and hot water (1930's semi, 3 to 5 occupants depending who's home from university, wife in 24 hours a day due to disability). So with the cost differential between gas and electricity, it's pretty close in cost.

Just the extra capital cost of the ASHP and installation to skew the figures.

Or any uprated insulation (etc.) you'd hope accompanied the ASHP installation.

That'd be outrageous for anything other than a huge poorly insulated detached house. The 'green upgade' wouldn't necessarily result in cost savings - as mentioned elsewhere, the ASHP roughly matches the cost of gas overall. I'm guessing the £350 is some sort of billing anomaly.

I'd guess the solar panels might give a £30-£50/month advantage over pre-retrofit setup, and the ASHP no overall cost advantage. The retention of gas, and a gas boiler, is odd. The way to cost savings is to do away with gas, and save on the standing charge at the very least. So I'm not sure what part of the design process that's all about.

Difficult to say. £2500 isn't outrageous, but is on the high side. Depends on your personal needs/habits as much as anything.

Solar panels, certainly, especially with a battery. But, and from my experience, going into solar on a hard cost/return basis makes the whole thing marginal at best, unless you can DIY install.

ASHP? Well . . .

Indeed. It needs a very careful assessment of the current system and its ability to heat satisfactorily at relatively low radiator temperatures. Then you'd need to look at insulation and ventilation.

It's not exactly rocket science but does need to be considered as a whole heat/insulate/ventilate system. A 30s semi isn't the worst to retrofit, but will likely have challenges.

Overall, they shouldn't. As mentioned above, I'd expect them to go down by about £40/month because of the solar. The gas situation needs to be clarified.

If it turns out they have gone up significantly I'd look very closely at the ASHP installation, and monitor the energy use of the 'pump.

Yes, me too. I follow the whole retrofit/grants thing reasonably closely and I've not seen a 'hybrid' example. If you happen to find out details of the scheme/council I'd appreciate it if you could post . . .

They could only ever meet a (probably) 13A load - ASHP can go way beyond that. And the highest demand is obviously in the winter, when there's no sun.

Not at all - solar isn't really going to help *directly* drive an ASHP to a significant extent. Most of the support will come from hot water heating when the sun's out. And indirect support for costs through export to the grid.

Ah right, I live and learn! Seems diametrically opposed to the 'eco' aspect of ASHP schemes, though. And 2 lots of heating plant to maintain. Look odd from a quick look.

Only if it's old. Modern condensing gas boilers are around 94%.

To get that figure you also have to improve the insulation and up-size your radiators in the same way as you have to do with a ASHP. The 95% figures are obtained with low flow/return temperatures and not the

Shocker: boiler company wants to sell boilers. They've done this kind of distraction before with 'hydrogen ready' boilers - spoiler, hydrogen heating isn't going to be a thing. But it gets the punters to install a 'future proof' bog standard gas boiler.

I haven't heard of anyone with a Worcester-Bosch heatpump, they seem to be a bit of an also-ran. They buy them in from someone else I think.

Theo