Radiators needed for ASHP and UFH?

[Dillsue]

1 hour ago, YorkieSelfBuild said:

• Heat Pump Model: We recommend the Cool Energy CE-IVT10-EVI, offering 4.89 kW to 10.47 kW at the above design temperature.  

So you've got a house with a max heat demand of 3kw and they're suggesting a HP with a minimum output of 4.89kw. That pump is likely gonna be short cycling for its whole life, cost you alot to run and pack up sooner than it should.

[Chanmenie]

6 hours ago, Dillsue said:

So you've got a house with a max heat demand of 3kw and they're suggesting a HP with a minimum output of 4.89kw. That pump is likely gonna be short cycling for its whole life, cost you alot to run and pack up sooner than it should.

I agree my heat loss was max 3kw so installer recommended the 4KW heat pump, which works fine, no short cycling, and it copes fine, although as I have previously said my flow temps are lower @ 21-28.  Hot water heats to 54, it’s set at 50 but always ends up at around 54 

[YorkieSelfBuild]

20 hours ago, JohnMo said:

Did you go via the MCS umbrella scheme?

 

The quoted ASHP is huge!

 

Install depends on what you need installed is it the whole heating system or just the heat pump and cylinder?

It's for UFH on GF as well.

 

It's still massive? Compared to 9.5kW, seems small

 

Cool Energy said they can supply for grant for extra £1k (commission after installation, documentation, etc).

 

The UFH is separate, so just installing pump and DHW.

[Dillsue]

13 hours ago, Chanmenie said:

I agree my heat loss was max 3kw so installer recommended the 4KW heat pump, which works fine, no short cycling, and it copes fine, although as I have previously said my flow temps are lower @ 21-28.  Hot water heats to 54, it’s set at 50 but always ends up at around 54 

I was commenting on yorkieselfbuilds 3kw loss and 10kw pump

[YorkieSelfBuild]

Just noticed, the IMS pump is 4kW, not 9.5kW. 

• Heat Pump: Riello NXHM004 4kW 230V

• Controller: Homely

 

That 9.5kW might be the output at outdoor temp of -3.4C?

[YorkieSelfBuild]

Update: after talks between architect and installer, the design is for high flow temp to rads so will need only small rads but in practice will run at same lower temp as UFH or unused. 

Still waiting to confirm if need only in bedrooms and if small enough to go under window seats so don't take up wall space. Estimated £900 extra, not terrible but still another 1k to budget

[JamesPa]

1 hour ago, YorkieSelfBuild said:

the design is for high flow temp to rads so will need only small rads but in practice will run at same lower temp as UFH or unused

Sorry but as you stated it (which is presumably how your architect stated it) that is complete and dangerous nonsense.  Rads need to be sized correctly for the desired flow temperature because you need them to emit the correct amount of heat at that temperature, and the amount of heat they emit is dependent on the flow temperature.  So (for example) a radiator that emits 1kW at 70C will emit only 370W at 45C and only 230W at 35C (the normal temp for UFH).

 

If they are not big enough for the design flow temperature the only things you can do are (a) increase the flow temperature above the design, until it is high enough that they emit the right amount of energy or (b) replace the rads or (c) freeze

 

If your architect actually meant this then he doesn't know what he is talking about!  Seriously.

 

 

Edited March 11 by JamesPa

[JohnMo]

8 minutes ago, JamesPa said:

Sorry but as you stated it (which is presumably how your architect stated it) that is complete and dangerous nonsense.  Rads need to be sized correctly for the desired flow temperature because you need them to emit the correct amount of heat at that temperature, and the amount of heat they emit is dependent on the flow temperature.  So (for example) a radiator that emits 1kW at 70C will emit only 370W at 45C and only 230W at 35C (the normal temp for UFH).

 

If they are not big enough for the design flow temperature the only things you can do are (a) increase the flow temperature above the design, until it is high enough that they emit the right amount of energy or (b) replace the rads or (c) freeze

 

If your architect actually meant this then he doesn't know what he is talking about!  Seriously.

 

 

Think what is going on and I said this on another post today is

 

Installer knows you really don't need radiators in bedrooms when they are above a heated area in a new build, well insulated house. But to tick a box they are specifically specifying a high flow temperature, to allow smaller radiators. The installer and architect have basically said that.

 

Reality is you run UFH as you would (no mixer hopefully) the radiators just tick away at UFH temp. Not really doing much, but everyone is happy(ish). Room upstairs take secondary heat from below anyway. Many state on here you just don't need them in bedrooms.

[JamesPa]

3 minutes ago, JohnMo said:

Think what is going on and I said this on another post today is

 

Installer knows you really don't need radiators in bedrooms when they are above a heated area in a new build, well insulated house. But to tick a box they are specifically specifying a high flow temperature, to allow smaller radiators. The installer and architect have basically said that.

 

Reality is you run UFH as you would (no mixer hopefully) the radiators just tick away at UFH temp. Not really doing much, but everyone is happy(ish). Room upstairs take secondary heat from below anyway. Many state on here you just don't need them in bedrooms.

OK it makes sense if that is in fact the case. 

 

I dont understand why the architect doesnt just say that, and instead feels obliged instead to spout nonsense!.  But it doesn't matter if it is in fact the case.

[Chanmenie]

7 hours ago, Dillsue said:

I was commenting on yorkieselfbuilds 3kw loss and 10kw pump

Yeah I know I was agreeing with you, and sharing my experience to back it up 

Edited March 11 by Chanmenie

[YorkieSelfBuild]

On 11/03/2025 at 10:23, Dillsue said:

I was commenting on yorkieselfbuilds 3kw loss and 10kw pump

It's actually 4kW, people got confused by a 9.5 kW number on one of the screenshots

[YorkieSelfBuild]

Anyway it looks like I'll stick with IMS as installers. Thanks for all the replies!

[Dillsue]

3 hours ago, YorkieSelfBuild said:

It's actually 4kW, people got confused by a 9.5 kW number on one of the screenshots

It was the cool energy quote at 10kw that I commented on. I had a similar daft quote from them

[sharpener]

5 hours ago, YorkieSelfBuild said:

It's actually 4kW, people got confused by a 9.5 kW number on one of the screenshots

 

With good reason. And you never explained what its significance was. What did IMS have to say about it?

[Nickfromwales]

16 hours ago, Dillsue said:

It was the cool energy quote at 10kw that I commented on. I had a similar daft quote from them

A lot of the bread and butter ASHP companies don’t really seem to put a lot, if any, proper thought into the type of dwelling, longevity by better design, and end user (occupant) comfort.

 

I’ve had a few to do quotes for me in an attempt to bring in more competitive pricing via my business, but these are inevitably just copy / cut / paste solutions by firms who are happily plodding along, busy anyways, whilst functioning like a sausage factory job to job.

 

Mention cooling or low heat requirements and they start telling you they “don’t work on properties like that” and don’t get back to you ever again, largely I expect because it requires thought, effort, and time (which to them is money).  Most seem quite short sighted but also very busy! 

[YorkieSelfBuild]

17 hours ago, sharpener said:

 

With good reason. And you never explained what its significance was. What did IMS have to say about it?

I haven't asked, tbh, don't think I need to now I know it's 4kW pump