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moving from ASHP to Gas Combi

Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 2 years ago

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ninja.tiger

(@ninja-tiger)

New Member Member

Joined: 2 years ago

Posts: 1

Topic starter 06/10/2023 4:55 pm

Hi all

need to pick a brain or 2.

I have a ASHP on property that has completely died on me ( moved in a few months ago - happy present for me) im looking to replace this with a gas Combi.

British Gas were hired to do the install. on the day of the install they called and said I have to get it drained first and they can't do it ( at cost to myself) after pushing back today they now said I can't have one as due to building regs ( property is 17yrs old) I can't replace an ASHP with gas system due to it changing the homes efficiency rating - they had no proof of this so just their word.

is this true or are they just messing me about.

thanks

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AllyFish

(@allyfish)

Prominent Member Contributor

Joined: 3 years ago

Posts: 518

09/10/2023 3:05 pm

Hi @ninja-tiger, I think British Gas might be stalling or not wanting to do the install. The job might not be as straightforward as a simple gas boiler replacement swap. Have they surveyed the property at all and had a look at the current ASHP system and what needs to change or it is all telephone/internet quoted prices?

Your ASHP might have several components that are associated with ASHPs; hot water cylinder, buffer, header, extra circulating pumps. They might not necessarily take these out, but they would not be needed with a combi providing CH and instant HW, and they would need disconnecting electrically, draining, making safe, etc. They might have to re-pipe some of the heating circuit to bypass components in your ASHP install that are not needed with a combi.

A newish hot water cylinder is more efficient for hot water than an instant combi. Bear that in mind if you have a hot water cylinder at the moment linked to the ASHP. Not using it and generating hot water instantaneously through a combi is a backward step. A system boiler with simple 3 way diverter valve and dual CH & HW timer switch can generate timed hot water, provide timed heating, or both, as and when required.

I'm not aware of any rules saying you cant revert to a gas combi in an existing property. New builds have slightly more design considerations to think about including Part L energy efficiency compliance and maximum 55degC heating system temperature. A 17yr old property should have a reasonable EPC anyway. Reverting from ASHP to gas combi may impact your home EPC for the worse if you're using combi for HW rather than a cylinder. EPCs largely assess the cost of energy rather than the CO2 impact or other environmental aspects. An average efficiency ASHP is roughly the same cost to run as an average efficiency gas combi. Combis are not that efficient for hot water generation however with a lot of wasted heat due to short cycling the boiler for small amounts of hot water.

I think you would get better service from a small independent heating engineer than British Gas. You need someone to take a proper look at the job before giving you a price. There may be costs that BG telesales office haven't remotely thought about until BG's installers have looked at the day's work list spotted 'ASHP replacement' and raised an alarm bell.

This post was modified 2 years ago 2 times by AllyFish

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Kev M

(@kev-m)

Noble Member Member

Joined: 5 years ago

Posts: 1276

10/10/2023 10:00 am

Posted by: @ninja-tiger

↑

Hi all

need to pick a brain or 2.

I have a ASHP on property that has completely died on me ( moved in a few months ago - happy present for me) im looking to replace this with a gas Combi.

British Gas were hired to do the install. on the day of the install they called and said I have to get it drained first and they can't do it ( at cost to myself) after pushing back today they now said I can't have one as due to building regs ( property is 17yrs old) I can't replace an ASHP with gas system due to it changing the homes efficiency rating - they had no proof of this so just their word.

is this true or are they just messing me about.

thanks

@ninja.tiger

Building regulations seem to suggest you can't replace an existing heating system with one whose C02 emissions are higher. See page 35 in the attachment below:

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"

That would rule out doing what you want.

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iancalderbank

(@iancalderbank)

Prominent Member Contributor

Joined: 3 years ago

Posts: 643

12/10/2023 2:51 pm

Posted by: @ninja-tiger

↑

I have a ASHP on property that has completely died on me ( moved in a few months ago - happy present for me) im looking to replace this with a gas Combi.

not quite sure why you are asking this on this board as clearly a retrograde step, but anyway in the spirit of helpfulness: if your house is already plumbed for an ASHP, thats the hard bit done.

Replacing the dead ASHP with a new ASHP, should be far simpler job than replumbing the house to run off a Gas Combi.

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4469

13/10/2023 1:43 pm

I agree with those who say don't/you cant do it, see regulation 5.4.

The only 'get out' is that this is guidance which, 'in the opinion of the Secretary of State meets the requirement'. The actual requirement is

As I understand it if you wish to depart from the guidance you will need to convince your building control officer that there is good reason to do so and that the requirement, which (must always be met) is still met. It may or may not be easy to do this.

As others have said a like for like replacement is surely the simplest. Grants done enter the equation and like for like replacement doesn't require planning consent provided it doesn't materially affect the external appearance of the building (TCPA 1990 55(2)