UFH, no insulation under pipes!

[Nick Laslett]

Maybe I’m just getting a bit grumpy!

 

Urban Plumber’s YouTube channel was one of my favourites for ASHP installs. He’s done a few collaborations with Heat Geek, and is on board with the BuildHub way of installing ASHPs.

 

But in his latest install video, he does a UFH system with no insulation under the pipes, just castellated plates. He explains that with a design heat loss of 8° from the ground, this means that there is little benefit to insulating under the UFH pipework. 
 

Maybe he is right, but watching the video just now it stuck me as totally wrong thing to advocate for. The section on UFH starts at 11:45 min. 

 

 

[marshian]

I viewed it slightly differently - I'm damn sure that insulating under a concrete floor is a very good thing to do from an energy loss perspective but think about it - if you have an existing house and to dig out the floors means massive work - you certainly aren't going to be living in it - if you can get 500 % efficiency with leaving the floors alone just a UFH layout above and a screed over the pipes why would you bother about getting a higher efficiency which isn't going to pass any cost benefit analysis

[JohnMo]

Statistics and numbers are a wonderful thing.

 

I've always said insulation is king but this does put a different spin on things. Not sure this approach would apply with a suspended floor, as it's outside air cold underneath. But as with all statistics you have to be careful.

 

Also note it is extremely likely the floor was then screeded, not the same as a foam former covered with OSB, heat transfer from pipes was good to the floor the way it's been done.

 

CoP and energy use are related, but very different. Running low flow temperature with a heat pump yields a good CoP, but doesn't mean the energy yield is all used. Insulation means more energy input can be utilised in the house and less escapes. Think in the video he said the heat loss was about 3kW at -3, assume 25% of that is floor losses, so about 5p per hour (CoP of 4) but only when it's -3, less than half that at 7 degs. So justifying ripping floor up to insulate would be low.

 

Good result for CoP, but maybe not so good for energy utilisation. But a cost effective solution overall. Just a matter of number balancing.

 

[Nickfromwales]

15 minutes ago, JohnMo said:

Statistics and numbers are a wonderful thing.

I agree with 96.7% of that. 

[Nickfromwales]

10 hours ago, Nick Laslett said:

But in his latest install video, he does a UFH system with no insulation under the pipes, just castellated plates. He explains that with a design heat loss of 8° from the ground, this means that there is little benefit to insulating under the UFH pipework. 
 

Maybe he is right, but watching the video just now it stuck me as totally wrong thing to advocate for.

If you look how wasteful most UK housing stock is to start with, there’s little reason to yank any hair out over a few pence per hour additional running costs vs comfort and wow factor, those things will be far more important to those who can’t afford to rip the floors up, and those who are happy that ignorance is bliss.

 

If someone says UFH can cost £5k and be done in a week, or £15k and take 3 weeks or more, you know which option most will go for. If the savings were more significant then prob an easier sell for the additional works, but when you factor in that some people may only be in that house for 5 to 10 more years before moving on, the subject gets the usual lip service and not much else.

 

If being run off an ASHP then the issue is further reduced, but not much more than gas I expect when you look at averaging energy costs across the day.

 

I’d fit the system the client asked me to fit, after giving them all the info (including pros cons caveats) and them then having then made their own informed decision.

[Marvin]

9 hours ago, marshian said:

I viewed it slightly differently - I'm damn sure that insulating under a concrete floor is a very good thing to do from an energy loss perspective but think about it - if you have an existing house and to dig out the floors means massive work - you certainly aren't going to be living in it - if you can get 500 % efficiency with leaving the floors alone just a UFH layout above and a screed over the pipes why would you bother about getting a higher efficiency which isn't going to pass any cost benefit analysis

In my humble opinion

 

I think this shows the different mindset between buying, doing up and selling, and buying, renovating and living in. With a bit of luck, insulation would last and have no running cost, however the additional energy used because of the lack of insulation would probably increase year on year. 

 

I think there's a lot of maths to find the reality to the cost difference and it would depend who's doing the work etc. For us facing a future of retirement and a reduced income it is better for us to have paid at the beginning (by spending less on holidays) then trying to find more money later. But then we intend to stay here. My brother used to say 'Pay now or pay later either way you pay'

The only thing is you do not know how much the future bill will be.

[marshian]

4 minutes ago, Marvin said:

For us facing a future of retirement and a reduced income it is better for us to have paid at the beginning (by spending less on holidays) then trying to find more money later. But then we intend to stay here. My brother used to say 'Pay now or pay later either way you pay'

The only thing is you do not know how much the future bill will be.

 

Agree with you there - I'm getting all the potential major expenditure done now before I retire because I'm damn sure it'll be a squeeze to do any of that on my pension

[Mike]

13 hours ago, Nick Laslett said:

He explains that with a design heat loss of 8° from the ground, this means that there is little benefit to insulating under the UFH pipework.

He's talking about the design temperature (i.e. the worst case the heating should cope with), and is correct in saying that when the outside air temperature is -3%C, the temperature below the floor will be warmer than that (he suggests 8 to 11°C).

 

With good insulation, the soil temperature may remain be in that range throughout the heating season. With poor insulation the soil temperature will rise much higher than that as the heating season progresses, because the UFCH will be - wastefully - heating it up.