Radiators needed for ASHP and UFH?

[Nickfromwales]

26 minutes ago, JohnMo said:

Do exactly the same without buffer or LLH

Then the circulation pump ramps up / down, so flow through the loops follows suite?

 

Long in-fill house with east (front) / west ends, so I wanted heat from each area (zone) to be in constant equilibrium; to steal heat from one place and distribute it to another. I remain sceptical about how well that would happen with reduced pump potential on the UFH loops at the manifold.

[JohnMo]

47 minutes ago, Nickfromwales said:

Then the circulation pump ramps up / down, so flow through the loops follows suite?

Pretty much, but only between 14 and 19L/min (less what goes via fan coil). 

 

This is the loops at min flow, so plenty of flow.

52 minutes ago, Nickfromwales said:

to steal heat from one place and distribute it to another

Do it for the same reason, living room gets plenty of solar gain so moves that heat to back of house.

[marshian]

1 hour ago, Nickfromwales said:

@marshian

 

"Speak now, or forever hold my piece"

 

Adam runs Heat Geek - you can contact him via the heat geek web page - he's pretty passionate about installs if any "heat Geek" accredited installer is over sizing a unit I reckon he'd be wanting to understand why

[YorkieSelfBuild]

4 minutes ago, marshian said:

 

Adam runs Heat Geek - you can contact him via the heat geek web page - he's pretty passionate about installs if any "heat Geek" accredited installer is over sizing a unit I reckon he'd be wanting to understand why

Ah, gotcha. Like emailing CEOs. Thanks

[YorkieSelfBuild]

1 hour ago, Chanmenie said:

I have 4KW pump and with the low flow temps the COP is  5.3 

How big is your house? Mines 118m².

 

I've read in newspaper articles about people not getting the right size ASHP, usually too small but possibly mine is too big.

[YorkieSelfBuild]

The price is £9.5k for ASHP and installation, minus BUS grant but adding more for the rads.

 

The architect said it was a good price, maybe they getting rid of stock, too big and R32?

[sharpener]

2 hours ago, YorkieSelfBuild said:

The 9.5 is the outdoor design temperature DOT -3.4C (from their website https://www.imsheatpumps.co.uk/blog/understanding-your-heat-curve/)

 

 

As I have a 12kW Vaillant their heat curves are all familiar stuff but doesn't really explain what the 9.5 figure is, what its dimensions are and whether there is another figure missing between "9.5" and "kW", can anyone else shed any light?

If IMS are your installers then it is odd their web site lists Vaillant and Nibe HPs which are both high end of the market but then they propose a Riello which is not.

 

Edited March 7 by sharpener

[marshian]

1 hour ago, YorkieSelfBuild said:

Ah, gotcha. Like emailing CEOs. Thanks

Yeah years ago I’d pay to search companies house for home addresses of directors and send them a letter to arrive with their cornflakes - life is different now

[YorkieSelfBuild]

2 hours ago, sharpener said:

If IMS are your installers then it is odd their web site lists Vaillant and Nibe HPs which are both high end of the market but then they propose a Riello which is not.

 

The architect explained it (or just said what IMS told him) as Riello being a budget sub brand of Viessmann but it seems both are owned by Carrier after it bought them, which is very different. 

 

Also I've seen Riello NXHM 12kW at £3800 inc VAT, so £5.5k for installation?

[JohnMo]

15 hours ago, YorkieSelfBuild said:

Not PassivHaus but quite close. MVHR, PV, SIPs, insulated, triple glazing, etc

House still being built so assume no air test.

And 120m²

 

So to out that into perspective, we are similar build, but have 192m² living space plus 26m² plant room/store, not quite twice the size. Our heat demand at -9 is 3.5kW.

 

So you should really be installing a 4kW heat pump. Or a 6kW if you want the ability to batch charge the floor in cheap periods (like a storage heater). But you need a decent depth of screed for that also.

[JohnMo]

Really wouldn't get to hung up on the R32 V R290. R290 is great if you need high flow temperature, not much different otherwise. More important is system design.

 

Your design with UFH and rads is generally fine. You don't have to have the rads on. You could have then on, and run the whole system cooler, plus the additional water volume is good. I would say the rads need to be designed for the same flow temp as UFH, so you have no mixers or additional pumps. Run the whole system as an open loop single zone. Just TRVs on bedroom rads if you need them.

 

Notes on design 

Installer cannot take credit for airtightness, unless you have a test certificate, they cannot take credit for MVHR if not installed and certified. These all drive the kW required up. The standard heat loss spreadsheet has some big air change numbers in it, which do not truly reflect a house that is airtight with heat recovery ventilation.

[ReedRichards]

12 hours ago, Nickfromwales said:

@marshian

 

"Speak now, or forever hold my piece"

 

Your piece of what?  

[marshian]

21 minutes ago, ReedRichards said:

 

Your piece of what?  

I assumed Glock or some other sidearm

[SteamyTea]

9 hours ago, marshian said:

send them a letter to arrive with their cornflakes

Yes, going to cost almost 2 quid to post it.

 

[marshian]

15 minutes ago, SteamyTea said:

Yes, going to cost almost 2 quid to post it.

 

Which is exactly why the internet is bloody wonderful 😉

[YorkieSelfBuild]

4 hours ago, JohnMo said:

Your design with UFH and rads is generally fine. You don't have to have the rads on. You could have then on, and run the whole system cooler, plus the additional water volume is good. I would say the rads need to be designed for the same flow temp as UFH, so you have no mixers or additional pumps. Run the whole system as an open loop single zone. Just TRVs on bedroom rads if you need them.

 

The architect is suggesting to IMS to use rads designed for high flow temp but actually run it at same lower temp used by UFH, so there's no mixing.

 

If rads were designed for low flow temp, would they be even bigger?

[sharpener]

34 minutes ago, YorkieSelfBuild said:

The architect is suggesting to IMS to use rads designed for high flow temp but actually run it at same lower temp used by UFH, so there's no mixing.

 

Then the rads will not emit their designed output so it is a nonsense. If it is a fudge and you are not actually going to use them as upthread it does not matter how big they are. OTOH if IMS are insisting on every room having adequate emitter(s) of its own it will not suffice.

 

34 minutes ago, YorkieSelfBuild said:

If rads were designed for low flow temp, would they be even bigger?

 

Yes. even to get the HP flow temp as low as 45C I needed to have mine uprated to 1.9x the area they were with a oil boiler at 65. To get down to UFH temps bigger again.

 

It should all be in the emitter schedule that came with the MCS quotation, mine had different columns for different flow temps so it was easy to see the effect.

 

 

Edited March 8 by sharpener

[Chanmenie]

15 hours ago, YorkieSelfBuild said:

How big is your house? Mines 118m².

 

I've read in newspaper articles about people not getting the right size ASHP, usually too small but possibly mine is too big.

190m2  well insulated 

[SteamyTea]

13 minutes ago, Chanmenie said:

190m2  well insulated

That does not really govern the heat losses.

Form is more important than area.

[Chanmenie]

3 hours ago, SteamyTea said:

That does not really govern the heat losses.

Form is more important than area.

No idea on form, but it seems ok, a small heat pump,  very low flow temps and it’s toasty and warm 😀

[SteamyTea]

20 minutes ago, Chanmenie said:

No idea on form

Form is just the thermal performance of the heat losses areas divided by the floor area, in this instance.

So a cube is better than an rectangular box, less glazing is better than lots.

[Beelbeebub]

Can I check what the issue is with fitting the specified rads? Is it aesthetic? Cost? Space? 

 

I've had to replace the failed UFH in some of my upstairs rooms with rads, 600x1400 (or maybe 1600, can't remember) with a flow temp sub 40c (it runs same flow temp as UFH). They work really well, despite feeling only slightly warm and you can feel the heat coming off them and the room warms up nice and quick. 

[YorkieSelfBuild]

On 08/03/2025 at 19:53, Beelbeebub said:

Can I check what the issue is with fitting the specified rads? Is it aesthetic? Cost? Space? 

 

I've had to replace the failed UFH in some of my upstairs rooms with rads, 600x1400 (or maybe 1600, can't remember) with a flow temp sub 40c (it runs same flow temp as UFH). They work really well, despite feeling only slightly warm and you can feel the heat coming off them and the room warms up nice and quick. 

All 3, cleaner without, added cost, stops wall being used. But also are they needed or is proposed design flawed? Plus the flow temp is 40C+, higher than for UFH.

[YorkieSelfBuild]

I got a quote from Cool Energy, £5800 inc VAT but not installation.

 

• Heat Pump Output: We recommend a heat pump with an output of 5.90kW.  

• Design Temperature: -3°C ambient temperature with a 35°C water flow temperature, suitable for underfloor heating (UFH).  

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

• Hot Water Cylinder Size: 200L, calculated at 50L per person plus an additional 50L.  

 

• 200L Pre-Wired Hot Water Cylinder  

• CE-B60 60L Stainless Buffer Tank  

• 25L Inhibited Glycol  

• System Filter, CAT6 Cable, Flexi Feet, Pre-Insulated Hoses  

• WiFi Adapter  

 

How much would installation cost?

No detailed plan, just ASHP and DWH supplied, is that normal?

[JohnMo]

17 minutes ago, YorkieSelfBuild said:

Cool Energy, £5800

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?

Edited March 10 by JohnMo