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Massive Electricity Cost for Running My Air Source Heat Pump

lucgw · 2022-12-07T08:04:04Z

Morning all, We recently had installed a Grant Aerona 13kw R3 inverter drive ASHP, cylinder and under floor heating throughout the house. I’ve been shocked at the daily cost of running it. Until a day or so ago I was setting each room thermostat to come on for an hour in the morning and an hour and a half in the evening (and also running around frantically turning off lights and appliances at their sockets). The daily usage was around £20 - which is not sustainable. Spoke with the manufacturer on Monday and they advised keeping thermostats in rooms at a low temperature rather than coming off and on. So I did this, but yesterdays usage was the most expensive it has been at nearly £24. Should daily costs be this high even with inflated energy prices? Right now I am looking at over £600 a month. Does anyone have any suggestions for trying to get costs down to a more sustainable level? The immersion switch at the front of the cylinder is off too. Thanks in advance for any help that can be given. Lucas

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Air Source Heat Pumps (ASHPs)

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Transparent

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26/11/2024 11:36 am

I don't think the insulation around those four external pipe runs is adequate.

Although I can't see how they arrange themselves to pass through a 100-125mm outer sleeve, the pipe clips have already compromised the wall thickness before the flow even gets there.

I also wonder if the installer has used Split-Insulation.
If so, then the split will be gaping open on the side which faces into the wall.

The approved method is to use adhesive to join the splits,
and for all bevel-cut ends around pipe elbows.

This then gets an outer layer of 'tape' to further cover the joins.

Armaflex and Kaiflex both manufacture UV-resistant external insulation.
It's usually sold as "solar insulation" because it gets used on roof-mounted solar-thermal collectors.

This post was modified 1 year ago 2 times by Transparent

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Transparent

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26/11/2024 11:41 am

As for the steel shed, I would expect to see around 100mm thick insulation sheet for the roof,
and around 75mm for the walls and door.

It must be draft-proof,
which may require neoprene rubber gaskets to be cut and glued around the pipe-exit holes.

I can provide further construction details if required.

The adhesive will be a 'contact' type such as this from Screwfix

Pipe insulation is usually best undertaken as a DIY task...
... preferably by someone with OCD!

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Econonsense

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26/11/2024 12:13 pm

@transparent Hi, I spend most of my time on international travel through work.

However, I have taken some time to check what you guys are saying and you're entirely correct.

See pics!

My first avenue was simply to get it all corrected, however I see now I will have to find the time to do most of it myself if I want it done well.

If I posted pictures of the horrific work they did in my house I think you guys would turn up with pitch forks outside their office!

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Transparent

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26/11/2024 12:39 pm

If you're going to take a DIY route to fixing the pipe insulation, then you should be asking for a rebate from the installer.

To calculate this, first ask them how long it will take them to remove what's there and do it again properly.
Then use £45/hour per person and add in the cost of buying the insulation yourself.
That should provide you with a good starting point.

They'll be super busy and wanting to get on with their next job rather than fix yours.
So the option of repaying you in cash will be tempting for them.

One possibility for you to consider is to make a rectangular box around those external pipes and seal them in...
... at least for the main vertical run.

There are PVC parts used by window-fitters and firms who clad facia boards, which could be fashioned into suitable boxing.

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Econonsense

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26/11/2024 12:55 pm

@transparent I couldn't agree more, my first idea when looking at it was to box it in.

There isn't enough clearance between the pipes and wall to insulate it much better.

My sons arm was recently injured quite badly, but as soon as he is fit I will lob him up in the loft to check the pipe insulation in there. I wouldn't be at all surprised if it is just the rockwool!

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Transparent

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26/11/2024 1:15 pm

Absolutely!
Child labour is well suited to the task of pipe insulation in confined spaces.

To seal where pipes enter the steel shed, I'd be using offcuts of EPDM rubber roofing material.
It's excellent for shaping around joins, and easy to cut.

You can glue it directly onto existing vertical surfaces.
So it's also a good choice to seal the top of your boxing.

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mark-h

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25/04/2025 5:26 pm

I know I'm late to this but I thought it would be worth pointing out that insulation of pipe runs outside the thermal envelope of the house is a building control matter. The installers should be responsible for complying with those regulations.

The relevant sections are 4.24 to 4.26 of approved document L:

ASSETS.PUBLISHING.SERVICE.GOV.UK "https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1133079/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf"

It's worth noting that the insulation thicknesses described in that document are for very high quality insulation (i.e. very low thermal conductivity and low emissivity). The building regs defer to BS 5422 for lower performance insulation, and that can have a huge influence. See the attached two tables for low and high emissivity insulation, cribbed from a verv old copy of BS 5422.

If we take 22mm pipe as a reference. The really high quality insulation would require only 8mm thickness, but if it was high emissivity then that would increase to 11mm and if it then had high thermal conductivity typical of the sort of neoprene like insulation (~0.04 W/mK) then you'd need 23mm insulation to meet the regulations. That's a big jump from 8mm!

As an aside, the building regs are a great source in some areas like this. IMHO they're easy to read and a model of clarity.

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25/04/2025 5:54 pm

I agree @mark-h The Building Regs are now very readable...
... although I do miss the sections of 'advisories' and illustrations of acceptable practices which used to be present.

There's an additional problem when selecting external pipe insulation because it has to be UV resistant of course.

The range of sizes available for installers to choose from is therefore reduced,
and especially so if they wish to use larger bore insulation around valve bodies.

Pipe Lagging offer a selection of 'solar' pipe insulation online, but it's expensive once you opt for sizes outside the common pipe diameters.

Another option is to swathe UV-resistant tape around the odd-sized sections and bends.
But my own experience with this approach is that the adhesive on the tape isn't good enough to hold firm around tight corners.
It needs supplementing with contact-adhesive at the edges.