UFH from the end of the radiator loop

[Andy]

I'm in the process of insulating the end room as our living room/snug. I'm probably going to be short on the heat output to make it super cozy as per my wife's needs. I don't want any more radiators on the walls. I've got 10 cm to play on the floor build up and was thinking of putting in UFH which could give me another 600w. Its a 15 square meter room+ 9square meter utility room. However the house is a long skinny one and the pipes are at the end of a long 30m run by the time they hit the two radiators the flow isn't great. I could probably put a small booster pump but even then its not going to get what I want temperature wise which is more than the 21ºC design temp. The heating is provided by a GSHP.
So...., I have a few options I think.
1. Take off the final radiator return flow and send it through the UFH pipe work with a small pump. The flow hit 55 at -14 last year so probably about 48 out of the return. I'm not sure if that it isn't too hot in for the screed. (27C max I think).

2. Take off the final radiator return and run it through a traditional mixer set up for UFH to ensure protection of the floor. The only problem then is if the pump is off where does the flow from the radiator go? I can't seem to find any pressure relief valves. I suppose I could have a 3 way valve that switches if the pump turns off thereby bypassing the UFH circuit.

3. Give up on UFH and get a split air-air heat pump. However I'm concerned that it might be a bit too noisy in the living room. It would never have to work too hard as I'll be starting from around 20 degrees.

Does anyone have other thoughts?

If anyone knows any company that does screed (fibre thin type) in Aberdeenshire that would be appreciated. I've only found Breedon from my googling.

[spread-tee]

I would go option 1 to be honest, if your flow temp is 55 deg your screed will be 10 deg lower at best and you could always use something like a remote sensor TRV to throttle the flow down if the floor does get too hot. I think you will struggle to get the flowrate required for a proper mixer and secondary pump from the existing rad feeds so option 2 might be tricky, you would be ok if you could tap into the feed and return directly from the HP but that probably involves a lot more pipery.

Desp

[nowty]

I would think your going to cause yourself more problems than it solves by modifying a working radiator heating system with a mixture of radiators and underfloor heating. You might not want another radiator but I don't quite understand why you cannot have one, surely that's the easiest and logical solution. Oversize it if the flow is poor with the and your saying you are only looking for 600w of extra heat output.

[Countrypaul]

Since you appear to have access to be the flow and return on the final radiator why don't you put the UFH heating in parallel with the final radiator, with a small pump and TMV - avoid the problem with the flow/return of the radiator being dependant on the pump and the TMV will ensure the flow temp in the UFH does not get to high.

[Stinsy]

I’d be very hesitant to add an extra pump in a living room. They all make noise, even the “quiet” ones.

I would suggest fitting additional or larger radiators. Vertical rads are a space saving way to increase output. If you fit smart TRVs to all the rads in your house those in other rooms will close once their room is up to temp and push more heat into your end-of-line living room.

55℃ is a very high feed temp for a heat pump system…

[Ken]

I notice you have not done the insulation yet and this could make a very big difference. You can use the 100mm to insulate the floor and ceiling/roof.

1) i hope you are not trying to run a system on small bore pipes. At 30m the main feed should be 22mm pipe with 16mm spurs to the rads. https://heatpumps.co.uk

Are you sure the circulation pump is big enough ? If the circulation rate is too low the pre rads will have had time to remove too much heat leaving little for the snug rads but also lowering the water temp too much fo the HP to operate efficiently

2) leave the system on longer to give the pre rads/rooms time to reach temp and scale down thus leaving more for the snug rads.

3) For just a few days then use a oil filled rad.

Ken

[Ken]

This is another consideration. https://heatpumps.co.uk/2021/03/09/radi ... -the-room/

We use a heat bulb in our light in the bath room. Its not on long but really makes a difference particularly with the heating still off as now.

[Andy]

Hi thanks for all your input. I think I have been persuaded to drop in another radiator t-ing off the existing radiator. Its probably a much cheaper option and gives me more insulation. I didn't really want to go back on to the 22mm pipe as its buried behind plasterboard and insulation. SWBO didn't want pipes on the walls which will make my life harder in 20 years time no doubt. I think I got a bit scared about the potential noise from the pump. I have quite a lot of flex left on the pump in the GSHP which does modulate. I never did get round to full rebalancing the radiators last year. Just a bit rough and ready so I can probably squeeze a bit more flow down the other end.

Stinsy: I agree that 55ºC is not good for a gshp, but in my defense that's probably ok at minus 14ºC . The system was sized for -5.6 so its doing ok getting to -14. It was flat out and the COP was only 2.7 at that point.

Ken: Yep, that's pretty much the reason the room has been ripped out is to put in tons of insulation. It is 28mm for first third and then 22mm for the main flow/return. 15 to all radiators. The system never. turns off as I have a NIBE F1255 which modulates everything.

[Joeboy]

When I read this yesterday I thought 'balancing' & triple radiator. Non invasive ways to improve room temp. I up sized a rad in our big room out back. About 700mm longer and stepped up from double to triple. The improvement in room heat up time was excellent and the existing pipework extensions are not noticeable.

Balancing the system made a huge difference too.

[AE-NMidlands]

I was wondering whether to put UFH in a room outside the footprint of the rest of the house (where it would be much prefereable to the radiator already there) but I realised that UFH prefers continuous low-temp input (often done out-of-hours,) whereas we run the gas central heating when we are up and about or likely to be sedentary, plus warming-up time beforehand. I had the impression that the intermittent relatively high temperature water circuit wouldn't work very well with a slab heat store.

The old-fashioned central heating provides background heat by most people's standards, plus we have a gas fire in the room we sit in in the evening.
Both (i.e. the whole system) need upgrading to make more efficient use of the gas though.
A