@temperature_gradient my point was to minimise the emergency install stress by giving people access to the grant beforehand to make their house “renewables ready”. That way the decision is easier, delay significantly reduced if not totally,  and less disruptive in what is already a difficult situation.  If a cylinder doesn’t need changing then it doesn’t - makes more of the grant available for other things - that list was just meant to be ideas.  I was glad to get rid of a noisy pump and a tank in the loft and would have done so regardless even though the existing tank was only 8 years old.  Incidentally many of these tanks aren’t insulated underneath for reasons that make no real sense - can you imagine that volume of water freezing in this country!  I couldn’t work out if building regs still applied to that but you don’t really want that amount of loft space uninsulated.

Posted by: @jamespa

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Posted by: @temperature_gradient

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why are virtually all installers converting the plumbing and fitting unvented cylinders, even when there's existing plumbing for a vented cylinder?

because historically heat pumps couldn't reach sufficiently high FT to heat a cylinder with the default coil size of 0.6 sq m.  Since R290 heat pumps can get to 75C this is no longer the case.  Unfortunately some (perhaps many) heat pump manufacturers still specify a min coil area I think

Posted by: @temperature_gradient

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One good move could be to require that all new hot water cylinders being sold and installed, have coils with enough surface area to ensure they work with a heat-pump. They cost a bit more, but there's an immediate benefit because they improve the efficiency of the gas boiler and speed up reheat, and they would be suitable for a new heat pump install avoiding the need to replace the cylinder at that point, so closer to a boiler swap.

Agreed, much like the latest building regs specify a max design temp of emitters of 55C, making it both heat pump ready and ensuring a condensing boiler actually condenses.  The boiler installer will probably still whack the FT up to max though, to ensure that it doesnt condense, the residents are less comfortable and pay more!

The trick with the Adia is it can balance the comfortable flow for the ASHP and stretch the DT in the old DHW cylinder, this allows you to circulate the water though the old cylinder a bit slower, avoiding noise and allowing the heat transfer a little longer on the under sized coil.

If you bolt the ASHP straight to the old cylinder with no smart control it runs slightly off balance, that said it does now look like Heat Geek do this often in their new approach. It takes longer for the cylinder to heat and makes the ASHP work a little harder but we are starting to see this is negligible.

The Adia has the ability to manage both ends and that the trick for it being on the undersized rads and undersized coil on the hot water.   

Posted by: @batpred

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Posted by: @batpred

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Are you suggesting heating dhw using the immersion heaters? 

No.  I am suggesting, based on what ashp-bobba has shown (and a bit of common sense) that the 'standard' practice of replacing existing DHW cylinders in almost all cases simply to get a larger coil needs to be questioned.  Historically heat pumps could only reach a FT of 55C and the practice dates from then.  Now they can reach 70-75C.

When getting estimates from the likes of Octopus and Heat Geek, the assumption is any cylinder could be kept. 

Posted by: @jamespa

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Do you mean the practice after the survey is in case R32 is being used, to add costs to replace it so that it warms a bit quicker? I assume a homeowner would not be too pleased with it, having in most cases paid for that survey.

Its more about making sure the heating circuits are compatible with the ASHP requirements, think of it this way, the under sized coil in the DHW cylinder is the same as the heating circuit is on microbore pipe, no one is saying it will not work but the ASHP has to work harder to make it work, you get more noise and you can have issues. at some point ASHP manufacturers will allow us to set maximum flow rates on ASHP's during set cycles, so imagine, if you try to shove 24ltr through a 22mm tube inside the cylinder it will be noisy. Installation companies dont take that risk so they change your cylinder to be compliant. If we can cap that flow to say 18ltrs, no noise but we are changing the available power from 8kW to 6kW to heat the cylinder, no noise bu 15 mins added to the heat up time, now whats more important, recovery time or noise?

Designing a whole heating system is a whole heating system thats needs to balance across the building, fitting the right cylinder helps something further down the line in one way or another. There was a time when some manufacturers would only warrant if you had their cylinder and ASHP, this was just for confidence that what the ASHP was bolted to would work, they all seem to be moving way for this condition now.

Posted by: @ashp-bobba

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Posted by: @batpred

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Posted by: @batpred

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Are you suggesting heating dhw using the immersion heaters? 

No.  I am suggesting, based on what ashp-bobba has shown (and a bit of common sense) that the 'standard' practice of replacing existing DHW cylinders in almost all cases simply to get a larger coil needs to be questioned.  Historically heat pumps could only reach a FT of 55C and the practice dates from then.  Now they can reach 70-75C.

When getting estimates from the likes of Octopus and Heat Geek, the assumption is any cylinder could be kept. 

Thanks.  My information is a bit out of date and things have obviously moved on, Im surprised it hasn't featured a bit more here).  That's great news if at least some installers, including some major ones, now dont insist on replacing cylinders when its not truly necessary.   

Posted by: @ashp-bobba

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, so imagine, if you try to shove 24ltr through a 22mm tube inside the cylinder it will be noisy. Installation companies dont take that risk so they change your cylinder to be compliant. If we can cap that flow to say 18ltrs, no noise but we are changing the available power from 8kW to 6kW to heat the cylinder, no noise bu 15 mins added to the heat up time, now whats more important, recovery time or noise?

The noise/flow rate thing is interesting and an angle I hadn't thought of.  I guess this is more of a problem with larger heat pumps (another reason not to oversize, as if there weren't enough already); my 7kW Vaillant delivers 20l/s through 22mm primaries to the cylinder and the pipework is silent.  

@jamespa we have only just been exploring this since 2026, in the purest form you should change the cylinder but, I believe in customer choice and my job is to best inform the customer, within reason give as many choices as possible and try my best to explain the pros and cons, as longe as we install the systems inline with the rules its fine, some companies add a plate so the can change the flow, its mostly about managing the flow rate through the cylinder, this is probably the 1 time you could do a LLH / Buffer and it would have a proper purpose, 1 pumps for heating 24l/pm 8kW and 2 pump for DHW 18l/pm 6kW this is crude but effective, Adia does this with smart control and then gives you room close control in every room, best described as managed open loop. 

There used to be a hard a fast rule that every room must be heated but we no longer heat most WC's especially if they are central in the building and if the customer insists we can allow a room to be under sized or not heated, now the way this works is the whole house is heated by the ASHP which is the rule, its just heated by the heat emitted by the room adjacent with the door open and of course is quite easy to add a rad later. 

We also stopped following the ventilation rules 2 years ago as we knew they were around 200% exaggerated, whats we did is we justified this, took the risk that of it turns out the ASHP was undersized we would change this, we had to change 2 out of 200, take my word for it, changing 2 allowed me to know how far to go, now that allows me to design within 10% of the line and not go under. HeatGeek now do this with their AI design software (shhh I think they copied me but I don't mind 🙂  I still do this long hand, perhaps I should do the heatgeek course if I ever get time.

Posted by: @jamespa

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Posted by: @ashp-bobba

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Posted by: @batpred

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Posted by: @batpred

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Are you suggesting heating dhw using the immersion heaters? 

No.  I am suggesting, based on what ashp-bobba has shown (and a bit of common sense) that the 'standard' practice of replacing existing DHW cylinders in almost all cases simply to get a larger coil needs to be questioned.  Historically heat pumps could only reach a FT of 55C and the practice dates from then.  Now they can reach 70-75C.

When getting estimates from the likes of Octopus and Heat Geek, the assumption is any cylinder could be kept. 

Thanks.  My information is a bit out of date and things have obviously moved on, Im surprised it hasn't featured a bit more here).  That's great news if at least some installers, including some major ones, now dont insist on replacing cylinders when its not truly necessary.   

Posted by: @ashp-bobba

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, so imagine, if you try to shove 24ltr through a 22mm tube inside the cylinder it will be noisy. Installation companies dont take that risk so they change your cylinder to be compliant. If we can cap that flow to say 18ltrs, no noise but we are changing the available power from 8kW to 6kW to heat the cylinder, no noise bu 15 mins added to the heat up time, now whats more important, recovery time or noise?

The noise/flow rate thing is interesting and an angle I hadn't thought of.  I guess this is more of a problem with larger heat pumps (another reason not to oversize, as if there weren't enough already); my 7kW Vaillant delivers 20l/s through 22mm primaries to the cylinder and the pipework is silent.  

 

we noticed that some cylinders start to sing when around 24/26ltrs so yes its the larger ASHP that casue a problem, if I am designing a 5kW system and the cylinder is good I think we would say keep it, if its on an 8kW system I think I would say go Adia or change it (same cost really but with Adia you get the room by room managed open loop) so Adia where you can I suppose if same cost

This veering of the topic onto cylinders etc is really interesting but should be in its own thread to make it easier to find in the future.  A conversation about the pros and cons of changing a cylinder, heating a room or not, leaving a door open etc isn't really one to be having at a crisis meeting!  Homeowners need to think through the implications when what they want is heating.  Now please, or at least by tomorrow.  

Posted by: @andrewj

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This veering of the topic onto cylinders etc is really interesting but should be in its own thread to make it easier to find in the future.  A conversation about the pros and cons of changing a cylinder, heating a room or not, leaving a door open etc isn't really one to be having at a crisis meeting!  Homeowners need to think through the implications when what they want is heating.  Now please, or at least by tomorrow.

I agree its an interesting topic in its own right, but it is also relevant to the topic of the thread ie how to deal with the distress purchase market.  The discussion tells me that, for the subset of the market that I identify at the start of the thread, changing the cylinder is not a given, in fact its probably reasonable to assume its not necessary.  TBH I thought that the latter was true from an engineering perspective ,but had the impression that the industry was still more or less immovable about the matter; thankfully it appears not.  That said I have seen a statistic that 80% of small to medium houses have combis, so a new cylinder (replacing nothing) is going to be required anyway.

I don't have the permissions needed to lift posts from one thread to another, but if you want to start a thread on changing cylinders or not, please do so.  It is as you say an interesting topic in its own right which we will need to find again! 

Posted by: @andrewj

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This veering of the topic onto cylinders etc is really interesting but should be in its own thread to make it easier to find in the future.  A conversation about the pros and cons of changing a cylinder, heating a room or not, leaving a door open etc isn't really one to be having at a crisis meeting!  Homeowners need to think through the implications when what they want is heating.  Now please, or at least by tomorrow.  

@andrewj Sorry for that, I though it was relevant, If you don't have to change the cylinder its more likely you will purchase a new ASHP system during a distressed purchase because i can give you temporary heating, keep the old cylinder on electric hot water mode and it all get put into the design. I dont mind if this gets put somewhere else, I will just try to help where I can.

Posted by: @ashp-bobba

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Posted by: @andrewj

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This veering of the topic onto cylinders etc is really interesting but should be in its own thread to make it easier to find in the future.  A conversation about the pros and cons of changing a cylinder, heating a room or not, leaving a door open etc isn't really one to be having at a crisis meeting!  Homeowners need to think through the implications when what they want is heating.  Now please, or at least by tomorrow.  

@andrewj Sorry for that, I though it was relevant, If you don't have to change the cylinder its more likely you will purchase a new ASHP system during a distressed purchase because i can give you temporary heating, keep the old cylinder on electric hot water mode and it all get put into the design. I dont mind if this gets put somewhere else, I will just try to help where I can.

It wasn't a criticism, just a thought that this interesting info might get lost!  I can see how it can (may??) help.  By not changing the cylinder, is this pushing additional cost further down the road, i.e. additional cost to what may be paid if a cylinder should have been changed during an install?  

When I had a boiler changed in 2016, they also changed 2 radiators and the cylinder and all the work was done in two days.  I think the cost was half the price of installing the heat pump last year (after grant) but could be equivalent to a planned install for a lot of homes.  Given it was November when it happened, we were very glad it only took 2 days!  I still think that a distressed purchase install is unlikely but an approach to preparing for the eventuality by pulling down on the grant early could help: it might actually improve the comfort of the existing boiler system and cost the homeowner practically nothing at this stage.

The Adia proposal looks really interesting.  I guess it's too early to have an idea of component failure rates?  Does it all run locally, or is it cloud based?  Shame it doesn't work with Octopus Cosy heat pumps.

Posted by: @andrewj

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Posted by: @ashp-bobba

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Posted by: @andrewj

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This veering of the topic onto cylinders etc is really interesting but should be in its own thread to make it easier to find in the future.  A conversation about the pros and cons of changing a cylinder, heating a room or not, leaving a door open etc isn't really one to be having at a crisis meeting!  Homeowners need to think through the implications when what they want is heating.  Now please, or at least by tomorrow.  

@andrewj Sorry for that, I though it was relevant, If you don't have to change the cylinder its more likely you will purchase a new ASHP system during a distressed purchase because i can give you temporary heating, keep the old cylinder on electric hot water mode and it all get put into the design. I dont mind if this gets put somewhere else, I will just try to help where I can.

It wasn't a criticism, just a thought that this interesting info might get lost!  I can see how it can (may??) help.  By not changing the cylinder, is this pushing additional cost further down the road, i.e. additional cost to what may be paid if a cylinder should have been changed during an install?  

When I had a boiler changed in 2016, they also changed 2 radiators and the cylinder and all the work was done in two days.  I think the cost was half the price of installing the heat pump last year (after grant) but could be equivalent to a planned install for a lot of homes.  Given it was November when it happened, we were very glad it only took 2 days!  I still think that a distressed purchase install is unlikely but an approach to preparing for the eventuality by pulling down on the grant early could help: it might actually improve the comfort of the existing boiler system and cost the homeowner practically nothing at this stage.

The Adia proposal looks really interesting.  I guess it's too early to have an idea of component failure rates?  Does it all run locally, or is it cloud based?  Shame it doesn't work with Octopus Cosy heat pumps.

 

I am happy if you want to start a new thread and tag me in to continue the conversation. I did not feel it was a criticism, I understand why you said it, I just think it is relevant in part or was.

You are correct it will cost more the change the cylinder at a later date as to keep the original cylinder you still complete all of the same works, all new connections and so on, you only save on the £1500 cylinder, so to fit the cylinder later it would likely cost £2100 + Vat where there was no Vat on the 1st install being renewables.

@ashp-bobba blimey!  That's the sort of price that is going to make someone say "forget it, bang a new boiler in".  A distressed purchase decision is going to be the wrong time for pretty much everyone except the die-hard, was seriously considering it anyway, home owner.  Once installation day arrives, it seems that 4-5 days is typical.  The lead up to that is weeks and months though waiting for a heat loss engineer, system designers, Q&A, permissions, then waiting for a team.  Fast tracking, even for a minimum-necessary install, seems essential.  I return back to the grant pulldown approach.  I think the biggest problem with this approach is likely to be bureaucratic as the government can't agree on a comprehensive insulation scheme right now.  That goes back to the big-thinking required that James alluded to.

Perhaps an EPC-heavy approach.  The current EPC process is money for old rope and next to useless.  That could be extended to provide the heat loss calculation and advice on fabric changes necessary for renewables as well as early access to funding.