ASHP Advice

[Ian B]

Hello Everyone, I'm new to Buildhub although have read posts in the past and appreciate how useful it is especially with individuals and their knowledge.

 

My position at the present time is I have 1930s semi in Cheshire which I suppose you could say is semi rural which is why it was heated by oil with no mains gas. We gutted the property and extended it with a single storey rear extension ( kitchen/ diner) and 2 storey side extension (garage, bedroom).

 

My provisions towards heating so far have been removal of existing floors downstairs with a make up of a new slab, 100mm insulation, underfloor heating pipes and a traditional dry screed ready for some form of tiles. I've renewed the loft insulation (now around 300mm).

The old external walls (no cavity) have been cladded internally with 50mm PIR and any new walls are insulated within the cavity.

 

I am asking for advice and opinions on which way to move forward with the provision of a ASHP. I have read some of the horror stories of poor planning and installation and how you can easily come unstuck with some of the very poor trades we have to put up with.

 

I recently read about 'The Cool Energy Shop' (imagine some other companies doing the same?)in a thread on here and how you can get your pump and cylinder from them through the Governments grant.

Then I've heard don't bother with the grant and just buy yourself, again I've read some of the companies not fit for purpose and you're not really benefitting from the grant because they just screw you over?

 

Finally I will say I have been sucked in at times to the whole thing of the negativity around heat pumps  (I think I saw a thread about certain media outlets, Guardian and others dissing heat pumps), so you start to question yourself and worry which way to go?

 

Sorry to rattle on but any help/advice would be appreciated by people who have done and from some of the guys in the know on here

Thanks Ian 

 

[Dillsue]

My experience with Cool Energy is they massively oversized our heat pump suggesting a 16kw pump for a 6.5kw heat loss. When I gave them the detailed heat loss calcs for comment, they never replied. There's a recent thread on here where they offered a 10kw pump for a 3kw heat loss. It's likely that sort of oversizing and attendendant high running costs are leading to the bad publicity you're reading.

[Ian B]

Thanks for the comments and yes I have heard similar. I take it you didn't use them, what did you do 

[JamesPa]

  On 14/03/2025 at 15:52, Ian B said:

Hello Everyone, I'm new to Buildhub although have read posts in the past and appreciate how useful it is especially with individuals and their knowledge.

 

My position at the present time is I have 1930s semi in Cheshire which I suppose you could say is semi rural which is why it was heated by oil with no mains gas. We gutted the property and extended it with a single storey rear extension ( kitchen/ diner) and 2 storey side extension (garage, bedroom).

 

My provisions towards heating so far have been removal of existing floors downstairs with a make up of a new slab, 100mm insulation, underfloor heating pipes and a traditional dry screed ready for some form of tiles. I've renewed the loft insulation (now around 300mm).

The old external walls (no cavity) have been cladded internally with 50mm PIR and any new walls are insulated within the cavity.

 

I am asking for advice and opinions on which way to move forward with the provision of a ASHP. I have read some of the horror stories of poor planning and installation and how you can easily come unstuck with some of the very poor trades we have to put up with.

 

I recently read about 'The Cool Energy Shop' (imagine some other companies doing the same?)in a thread on here and how you can get your pump and cylinder from them through the Governments grant.

Then I've heard don't bother with the grant and just buy yourself, again I've read some of the companies not fit for purpose and you're not really benefitting from the grant because they just screw you over?

 

Finally I will say I have been sucked in at times to the whole thing of the negativity around heat pumps  (I think I saw a thread about certain media outlets, Guardian and others dissing heat pumps), so you start to question yourself and worry which way to go?

 

Sorry to rattle on but any help/advice would be appreciated by people who have done and from some of the guys in the know on here

Thanks Ian 

 

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I have a 1930s property in not so rural Herts/Essex borders and I have recently replaced my gas boiler with an ASHP.  Like you my (originally solid) walls are insulated with 50mm PIR, and I have 300mm loft insulation.  I dont have floor insulation.  Heating is by radiators.  I am very pleased with the heating performance (Its much more stable than I ever got with the gas boiler) and its working out about 12% cheaper like for like to run.  Its also more comfortable - low temperature heating is a bit of a revelation, the reduced thermal gradients both in time and space are noticeable.

 

However you are right that there are quite a few poor installers out there who will fit buffer tanks, low loss headers or plate heat exchangers, a heat pump double the size that you need, lots of 'smart' external controls (the worst type unless specifically designed for heat pumps, which most are not), and will then turn the flow temperature (which is the critical parameter) up high, all of which clobber efficiency.  Actually these people are really just grant harvesters and wont be around once grants subside, but in the meantime they are giving the industry a bad name.

 

I would strongly advise you to take a bit of time to understand the technology, perhaps starting here where there is a good newbies guide, get several quotes and ,if you have the time, take your time over it.  If you know how much oil you use per annum you can sense check any heat loss surveys.  You will need to have a heat loss survey done as the basis of the design, but be warned that they can be complete nonsense - for example there are definitely installers who will refuse to take into account your wall insulation because they cant see it, and can easily get it wrong by a factor of 2 - which can matter a lot!   There are also some very good installers out there who will take care to sell you an excellent, well matched system (and please note the system design matters more than the heat pump 'brand'.

 

If you post your floor area and annual oil consumption, plus tell us a bit about your current heating patterns and age of boiler, we can get some idea of what you might (subject to survey - and then sanity checking of the survey) need.

 

Cool energy sell a limited range of heat pumps and, whilst they have a good reputation in many respects, it would be a mistake to limit your choice at this point. 

 

Hope that helps

 

 

[Ian B]

Thanks JamesPa for taking the time with your reply, I will have a read through the link you sent. We have had the house for some time and stripped it out without ever using oil so cannot give my annual use of oil.

I bought the ufh pipe with a bit of a plan (as you touched on it of how good the calcs are?)

The floor area is 173m2 although this seems to include the garage?

I would have said it was more like 150m2 of rooms to be heated.

Heat losses are just under 4kw

[Ian B]

I appreciate what you say about learn and understand about the technology and I have read this before and the advice is obviously well meaning. What a sorry state we are in (I wonder if it's just our wonderful country because heat pumps are common place and have been for many years in most of Europe) because let's face it some people wouldn't be able to understand or work out what they need. Really why should they if they're paying someone who should be an expert in their particular field.

Sorry for the rant but it's quite sad how things are 

[Dillsue]

  On 14/03/2025 at 16:25, Ian B said:

Thanks for the comments and yes I have heard similar. I take it you didn't use them, what did you do 

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Collecting parts at the moment. Once it warms up will swap/fit new radiators and then get the heat pump fitted. We're having a hybrid system with WBS and LPG boiler as backups so aiming to have a slightly undersized HP with the WBS topping the heat up on the very few freezing days we have.

[SteamyTea]

  On 14/03/2025 at 18:09, Ian B said:

Really why should they if they're paying someone who should be an expert in their particular field

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This is true in so many fields, opinion is often quoted as fact.

That happens on here as well.

 

You understand how different heating systems work, is it the concept of a low temperature system that you find hard to accept.

As I frequently say, temperature is not energy.

[MikeSharp01]

  On 14/03/2025 at 16:03, Dillsue said:

My experience with Cool Energy is they massively oversized our heat pump suggesting a 16kw pump for a 6.5kw heat loss. When I gave them the detailed heat loss calcs for comment, they never replied. There's a recent thread on here where they offered a 10kw pump for a 3kw heat loss. It's likely that sort of oversizing and attendendant high running costs are leading to the bad publicity you're reading.

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I have started down the road with them and they have accepted our heat loss calcs and that their smallest unit will do the job - so almost the reverse of this. the problem now is that the smallest unit is not MCS certified yet - they are working on getting it certified and we can proceed. 

[JamesPa]

  On 14/03/2025 at 17:53, Ian B said:

Thanks JamesPa for taking the time with your reply, I will have a read through the link you sent. We have had the house for some time and stripped it out without ever using oil so cannot give my annual use of oil.

I bought the ufh pipe with a bit of a plan (as you touched on it of how good the calcs are?)

The floor area is 173m2 although this seems to include the garage?

I would have said it was more like 150m2 of rooms to be heated.

Heat losses are just under 4kw

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4kW with a reasonably well insulated semi 173 sq m is definitely very plausible.  My 200sq m detached in 7kw (two professional surveys, each taking 3hrs, got to 16kW - perhaps you can understand why I am sceptical about heat loss surveys)

 

So if this is correct you are looking at a 5kW pump perhaps, directly connected to the heating system without 'hydronic separation'.  UVC for DHW and a diverter valve to switch between the two.  Hopefully, given you have UFH, operating at 35 or below.  Is it UFH or rads upstairs.  You can only really run at one flow temp for space heating so if its rads they will need to be large enough to run at the same low FT as the UFH.

 

Should be simple provided the pipework or locating the outdoor unit doesn't cause a problem.  Just be aware that quite a few 4 or 5 kW units in fact software limited higher capacity units.  The problem with that is they wont modulate down as far as you ideally need in the shoulder season.  By the same token there is not much point in buying a 5kW unit if it is in fact the 8kW unit software limited.  Good installers have twigged this and therefore avoid certain models in any given range.  The combination of physical size and refrigerant charge frequently gives the game away.

 

I would recommend you contact several installers including one that is Heat Geek certified.  Heat geeks tend to be more expensive, but purport to understand the technology better.  You will want to hear/read what they say.  The website I pointed you to does provide recommendations for installers (I have no connection and cant vouch for them).  I would eliminate any that insist on fitting a buffer or LLH (low loss header), other than a 2 port volumiser.

 

 

  On 14/03/2025 at 18:09, Ian B said:

I appreciate what you say about learn and understand about the technology and I have read this before and the advice is obviously well meaning. What a sorry state we are in (I wonder if it's just our wonderful country because heat pumps are common place and have been for many years in most of Europe) because let's face it some people wouldn't be able to understand or work out what they need. Really why should they if they're paying someone who should be an expert in their particular field.

Sorry for the rant but it's quite sad how things are 

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I agree with the sentiment, but we have to deal with the world as it is not the world as we would like it to be.  In this field, as in many others, it helps to be an intelligent customer and increases the chances of getting a good job.  For the past 20 years many, perhaps most, of us have been paying 10% more for our gas heating than we needed to, and enjoying lower levels of comfort, because 'the industry' shunned weather compensation (which was made mandatory in some countries)  and set up our condensing boilers so that they mostly don't condense.  Unfortunately the only thing to be learned from this is not to trust the heating industry! 

 

From what we hear there are other countries that are in not dissimilar situations so we appear not to be unique.

 

I should stress once more that there are good installers out there, the trick is to avoid the bad ones and this is where a bit of understanding can come in useful.  This comment probably applies to almost any aspect of building, and indeed many other trades!

 

 

Edited March 14 by JamesPa

[Ian B]

Again thanks for the replies 

[Conor]

Suggest 150mm floor insulation with 50mm liquid screed rather than 100mm insulation and 100mm dry screed. You want as much insulation as possible (to a point)

[Dillsue]

  On 14/03/2025 at 19:15, MikeSharp01 said:

I have started down the road with them and they have accepted our heat loss calcs and that their smallest unit will do the job - so almost the reverse of this. the problem now is that the smallest unit is not MCS certified yet - they are working on getting it certified and we can proceed. 

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That's good going. I played email ping pong for a few days, then they asked for the detailed calcs which I sent them and they never replied.

[Ian B]

  On 15/03/2025 at 14:59, Conor said:

Suggest 150mm floor insulation with 50mm liquid screed rather than 100mm insulation and 100mm dry screed. You want as much insulation as possible (to a point)

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Not sure if you've got that quite right, but I don't know enough?

You state 150mm insulation and 50mm liquid screed.

Yes I suppose 150mn insulation but I think with PIR you get to a certain thickness and the gains are minimal?

The screed at 50mm I would be concerned with cracking and heat loss compared to a thicker floor as the concrete acts as a thermal store?

[Nickfromwales]

140/60 would be fine.

 

  On 16/03/2025 at 19:31, Ian B said:

The screed at 50mm I would be concerned with cracking and heat loss compared to a thicker floor as the concrete acts as a thermal store?

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A common misconception. A 50mm screed will be fine, just more often than not anyone tiling over it would insist in a decoupling membrane to cover their arses.

 

The thicker the screed the longer to heat up, and at 50mm you'll be able to turn them on/off with reasonably accuracy without any issues, as they'll act a bit like a radiator would in the same room, just the end result would be far more comfortable.

 

I've had my screeder lay from 50mm all the way down to 10mm, primer bonded, with a dry mix S&C screed, and we tile straight onto that with BAL ultra flex adhesive, only one tile hairline cracked and that was where the new UF heated floor met the existing original concrete slab (as I was young and still a bit wet behind the ears and didn't allow an expansion / break there.

[Nickfromwales]

  On 14/03/2025 at 18:09, Ian B said:

I appreciate what you say about learn and understand about the technology and I have read this before and the advice is obviously well meaning. What a sorry state we are in (I wonder if it's just our wonderful country because heat pumps are common place and have been for many years in most of Europe) because let's face it some people wouldn't be able to understand or work out what they need. Really why should they if they're paying someone who should be an expert in their particular field.

Sorry for the rant but it's quite sad how things are 

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I did plant room & M&E on what was essentially a 6 bedroom bungalow (split level) and they had spent £100k on 1st and 2nd fix plumbing. What a shower of shite, and they said they were experts. In their small-print was a statement that they couldn't guarantee results as they weren't doing the plant room / end equipment etc. Client then told me it was over their heads and they refused to quote for it..... 2000L of stored pressurised cold mains in the garage (detached) and then found the 32mm pipe that appeared each end actually then reduced to 25mm for the 75-80m between the buildings ffs. Told the client to dig it out and swap it to a 50mm run, and then the showers all worked in unison.

 

No duct for ASHP or GSHP so we ended up having to install a 3phase electric boiler as no gas on site.

 

  On 16/03/2025 at 19:31, Ian B said:

Yes I suppose 150mn insulation but I think with PIR you get to a certain thickness and the gains are minimal?

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There is a definite benefit going up this extra 50mm, certainly not minimal. Ideally you'd have rads on the wall with 100mm of insulation vs a heated screed on top of it. 100mm is 'good enough', but 140-150mm is way better.

[SteamyTea]

  On 16/03/2025 at 19:31, Ian B said:

Yes I suppose 150mn insulation but I think with PIR you get to a certain thickness and the gains are minimal

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That is true for all materials, just how nature works.

You really need to decide how willing you are to pay for future heating in the knowledge that a fraction of it is lost.

You only fit floor insulation once, thermal losses are constant.

[Conor]

  On 16/03/2025 at 19:31, Ian B said:

Not sure if you've got that quite right, but I don't know enough?

You state 150mm insulation and 50mm liquid screed.

Yes I suppose 150mn insulation but I think with PIR you get to a certain thickness and the gains are minimal?

The screed at 50mm I would be concerned with cracking and heat loss compared to a thicker floor as the concrete acts as a thermal store?

Expand  

 

We've 50mm liquid screed on top of 200mm insulation across 115m². The diminishing returns for floor insulation seems to kick in at ~200mm (PIR) or more, going by people's experiences here. 50mm screed will not crack, unless you drop an anvil or something! I do admit, there there is a subtle bounce / resonance about it, you can tell it's not "solid".

[Nickfromwales]

  On 16/03/2025 at 21:30, Conor said:

you can tell it's not "solid".

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Yup, at 50mm you just know. It's like when you have floating wooden flooring vs when it's been bonded down.

[Dillsue]

  On 16/03/2025 at 19:58, SteamyTea said:

You only fit floor insulation once, thermal losses are constant.

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A concept often missed in our quick/cheap fix world