UFH pipes in 100mm of concrete / screed

[shackles]

Hello, 

 

Having my extension floor poured soon and have had conflicting advice from various sources. 

 

I have 150mm PIR with UFH pipes stapled to it at 150mm spacings. 

 

I have allowed for 100mm of screed going over the top. Some people say that all you need is 50mm of screed and that the UFH won't work properly with 100mm...

 

Does anyone have UFH pipes in 100mm of concrete or screed & does it work ok?

 

Cheers!

 

 

[Mike]

Yes, 100mm depth works fine. It just takes the floor longer to respond to any changes in settings (compared to thinner screeds) as you have a larger mass to heat up / cool down.

[Chanmenie]

Yeah as Mike said it will work fine, probably better than in a 50mm screed.

The house I currently live in has UFH pipes in at least 100mm concrete and is fine, the whole estate of approx 500 houses is the same.

Norfolk Homes have been doing it this way for years.

Ive done my new build the same. 

Anyone who tells you it won’t work doesn’t know what they are talking about.

[JohnMo]

24 minutes ago, shackles said:

Does anyone have UFH pipes in 100mm of concrete or screed & does it work ok?

Works no problem, I even have 300mm pipe spacing, 100mm concrete and again no issue. But they are a bit of a learning curve.

 

Few things I found through experimenting, you need to be aware of.

 

Changing floor temperature and house is quite a long process (many hours), so a normal thermostat is just rubbish and you get big under and over swings. You really need to use a 0.1 Deg hysterisis thermostat.

 

You cannot use room compensation as the algorithms cannot cope with the long reaction times.

 

Don't bother trying to do temperature setbacks, they generally don't work the way you expect.

 

You cannot switch the heating on at work and hope to have a warm house when you get home (unless you do when you arrive at work).

 

There is zero point zoning, run as a single zone.

 

Two options of how to operate, charge the floor and use like a storage heater, or continuously feed the floor at a low temperature.  I have done both and they work equally well. 5 degs difference in flow temp is the difference in the two methods.

 

I am on E7 with ASHP, battery and charge the floor at 33 degs (overnight), for between 7 and 12 hrs depending on outside temp, automated with a timer thermostat. Generally it takes another 12 to 18 hrs to cool enough for the heating to come back on again. The wife was quite shocked the other week when it was near freezing outside (6pm) and I told the heating actually went off at about 10am and was not coming back on until after midnight. You can't do that with 50mm screed.

[Chanmenie]

Good post John 👍

[shackles]

Thank you for the responses. I had read various articles on different websites stating that 100mm did work well. 

 

Then I posted on a Facebook group and everyone said I was crazy for even mentioning 100mm and that the UFH will not work in that depth and that it was a waste of money etc etc. 

 

I have seen people mention the NeoStat WiFi thermostat with the hub - is this a good option that includes  0.1 Deg hysterisis? Never heard of this before.

 

Thanks.

[JohnMo]

12 minutes ago, shackles said:

NeoStat WiFi thermostat with the hub -

 

Don't waste your money, the switching threshold (hysterisis) is 0.5 at best, 3 Deg at worst - just get a Computherm Q20RF or Q7RF from Amazon for £60 or less the Q20RF is nicer to use. No zone valves or actuators on the manifold, if you have radiators, get an IVAR low temp mixer valve with pump, and drive the pump on and off with the thermostat.

 

16 minutes ago, shackles said:

had read various articles on different websites stating that 100mm did work well. 

 

Then I posted on a Facebook group and everyone said I was crazy for even mentioning 100mm and that the UFH will not work in that depth and that it was a waste of money etc etc. 

Just shows they don't know much.

[Conor]

We originally had a spec of 150mm PIR and 100mm s&c screed. Changed to 200mm insulation (150mm PIR and 50mm EPS) and 50mm liquid screed. No price difference and have less heat loss. 

 

And the neostats are shite, stay away.

Edited March 8 by Conor

[HughF]

125mm ish here…. No stat, fixed flow temp of 28… might turn it off next week, it has been on 24/7 since late October. Works perfectly.