Under joist UFH - any good?

[SBMS]

Currently looking at UFH options for our first floor - posi joists with 22mm chipboard.  

Heating contractor is recommending nuheat clippa plate. We have 480mm joist spacings so can probably fit one spreader between joists. 

 

Has anyone had good (or bad) results from
UFH That is between and under joists?

 

(We have decided to have heating upstairs

for belt And braces even though might not

be used much. )

Edited April 3 by SBMS

[Ajm]

we used something similar in our upstairs, under engineered wood floor. 

 

It works fine, bearing in mind it does not behave thermally the same way as underfloor heating embedded in screed downstairs. It heats up much quicker but also cools down more quickly as there is no thermal store.

 

However, since we only have the one room upstairs and it is open to the ground floor we have rarely had to use the upstairs heating. The only time we did was back in 2011 (I think) when we had a few days of -20 outside temperature and we needed the extra heat in the house. The air source heat pump continued to work well even down at those temperatures. And the upstairs UFH did its job.

 

 

[Nickfromwales]

I used this company LINK for the last job where the same decision was agreed on between myself and the client; futureproof for anticipated downstream sale plus the slight possibility that it would be needed.

 

That was enough to justify the small uplift in my fee to do 50-60% of the area of each of the 3 upstairs spaces, as there was no need to 'go mad' up there (MBC PH TF).

 

The biggest thing is to use a load of fixings to ensure as much of the alu is in firm contact with the timber deck as is possible. Go bloody nuts with that; we used an air stapler and just went berserk with a couple of boxes of 1000 going in a wink (job below).

 

 

[SBMS]

  On 04/04/2025 at 11:52, Nickfromwales said:

I used this company LINK for the last job where the same decision was agreed on between myself and the client; futureproof for anticipated downstream sale plus the slight possibility that it would be needed.

 

That was enough to justify the small uplift in my fee to do 50-60% of the area of each of the 3 upstairs spaces, as there was no need to 'go mad' up there (MBC PH TF).

 

The biggest thing is to use a load of fixings to ensure as much of the alu is in firm contact with the timber deck as is possible. Go bloody nuts with that; we used an air stapler and just went berserk with a couple of boxes of 1000 going in a wink (job below).

 

 

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Isn’t this on top of the floor?

[Nickfromwales]

  On 04/04/2025 at 17:24, SBMS said:

Isn’t this on top of the floor?

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These ones are sat on top of the joists, others we did from the underside with the plates I linked to (actually we used the single runs and overlapped as the joists were at 400 oc).

 

You need to go slow and steady when lacing the pipes in from underneath to avoid kinking them. And avoid what I did which was sleep on my feet and wrap the pipe around a joist and then notice after I’d tucked it in that void lol. 

[SBMS]

  On 04/04/2025 at 17:47, Nickfromwales said:

These ones are sat on top of the joists, others we did from the underside with the plates I linked to (actually we used the single runs and overlapped as the joists were at 400 oc).

 

You need to go slow and steady when lacing the pipes in from underneath to avoid kinking them. And avoid what I did which was sleep on my feet and wrap the pipe around a joist and then notice after I’d tucked it in that void lol. 

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Are the ones that you fit under the joists effective?

[Nickfromwales]

  On 04/04/2025 at 19:53, SBMS said:

Are the ones that you fit under the joists effective?

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Sorry! Yes, very effective but need a higher flow temp.

In that pic was 2x 16mm pipes in spreader plates, then 22mm P5, then 6mm ply, then tile adhesive and porcelain tiles.

You’ll defo need a dedicated UFH manifold for the upstairs circuits so you can set different flow temps for GF and FF.