Underfloor heating pipe spacing

[Conalmcn]

Im currently planning my underfloor heating setup and keep hearing conflicting reports on pipe spacing. Its a new build property with an ok standard of insulation and will be as air tight as I can make it along with mvhr. 

 

Originally I'd like to run the system (ufh downstairs and radiators upstairs) using an oil boiler and leave it with the ability to move to an alternative source in the future such as gshp. From what I gather the spacings are down to the heating demand of the room but is there negatives to using say a 100mm spacing over 150/200 or is the only downside the initial material cost? 

[Dreadnaught]

Yes, it is down to heating demand. I was advised by someone experienced with UFH and he specified 125 mm spacing for 125 m² new-build well-insulated bungalow.

 

Only downsides that I can think of are: pipe cost, cost (and space) of a bigger manifold, cost of labour to lay the extra pipe. Unless you are DIY-ing, labour is about the same as materials (if not more).

[JohnMo]

Mines at 300mm spacing, over 190m2.  Lounge has two loops, the other rooms a single loop.  Total 404m of floor tubing.  Low energy house though.

 

No issues, UFH flow temp at 35 degs.

 

But closer spacing, can run cooler.

[ProDave]

200mm for me as that worked out nicely with 400mm joist centres.  Works very well.

[Dan F]

Calculate your heat demand and then model it in loopcad with different spacing.  This will give you power output for different flow temperatures.  If using 150mm centers means you can use a lower temperature then it may be advantagous.  In a very highly insulated house 150mm is typically too close though, and even 200mm you can run at <30C, so it depends on house and heat demand.

 

 

Edited January 23, 2022 by Dan F

[Simplysimon]

contact https://www.wundagroup.com/underfloor-heating/ and ask for a quote. they will specify the spacing

[Temp]

I don't see any down side to a close pipe spacing apart from material cost.

 

I suppose if you had very large rooms that might mean you need two loops in one room as they recommend each loop is less than 100m. That means extra ports on the manifold but not a big problem. 

 

I would certainly consider a buffer tank because oil boilers can't modulate so they can only cycle when (for example) only one loop us calling for heat. 

[Conalmcn]

Thanks all. I think the main issue is making sure that I'm future proofing the design as much as possible and if there was any negatives of smaller pipe spacing apart from pipe/manifold cost. I've had mixed responses from various sellers with some saying that under 150mm was not recommended but with no real justification of why.

[Conor]

In the grand scheme of things an extra 100m or so of pipe and a 8 port instead of 6 port manifold is pittence. We went for 200mm spacing in bedrooms and smaller rooms, 100mm ish in halls and large open spaces.

[Adsibob]

26 minutes ago, Conalmcn said:

Thanks all. I think the main issue is making sure that I'm future proofing the design as much as possible and if there was any negatives of smaller pipe spacing apart from pipe/manifold cost. I've had mixed responses from various sellers with some saying that under 150mm was not recommended but with no real justification of why.

It might be because the narrower your pipe spacing the more 180 degrees your pipe needs to go through to achieve serpentine which is the most common layout. Too many 180 degree turns could arguably affect flow. Whilst that can be mitigated by not laying serpentine, you would still have more distance to cover with your pipes, which might lead to unnecessarily long loops or excessive number of loops.

 Another possibility is that pipe has a limited turning radius. The pipe we laid under our screed had a minimum turning radius of about 80mm so the minimum spacing was 160mm. We ended up with softly more than this, I think around 170mm siding because my fitter was worried about kinking it if we went too close to the pipe’s limitation. Not moved in yet, but with the water running at 28C for the mo, screed  already feels warm to the touch, so I guess it’s worked.

Edited January 24, 2022 by Adsibob

[Conalmcn]

14 minutes ago, Conor said:

In the grand scheme of things an extra 100m or so of pipe and a 8 port instead of 6 port manifold is pittence. We went for 200mm spacing in bedrooms and smaller rooms, 100mm ish in halls and large open spaces.

As you say the cost really doesn't factor into it as the extra cost is negligible in comparison. I just don't want to be putting something in thats counterproductive.

5 minutes ago, Adsibob said:

It might be because the narrower your pipe d spacing the more 180 degrees your pipe needs to go through to achieve serpentine which is the most common layout. Too many 180 degree turns could arguably affect flow. Whilst that can be mitigated by not laying serpentine, you would still have more distance to cover with your pipes, which might lead to unnecessarily long loops or excessive number of loops.

 Another possibility is that pipe has a limited turning radius. The pipe we laid under our screed had a minimum turning radius of about 80mm so the minimum spacing was 160mm. We ended up with softly more than this, I think around 170mm siding because my fitter was worried about kinking it if we went too close to the pipe’s limitation. Not moved in yet, but with the water running at 28C for the mo, screed  already feels warm to the touch, so I guess it’s worked.

I had hoped to use counterflow layout. I was thinking of the loop issue but may modify certain rooms if they where just over 2 loops and make the spacing match the loops as such. 

[farm boy]

Has anyone used 100mm spacing for UFH pipes on the ground floor, my build has natural ventilation (trickle vents) and I cannot not make a wider spacing work on my thermal calculations spread sheet.

[Nickfromwales]

48 minutes ago, farm boy said:

Has anyone used 100mm spacing for UFH pipes on the ground floor, my build has natural ventilation (trickle vents) and I cannot not make a wider spacing work on my thermal calculations spread sheet.

Yes, I do on most of my jobs as they’re destined to be coupled up with an ASHP. 

Only issue is the extra pipe, extra manifold ports but benefits are more volume of water per m2 which will help convey the heat energy in the pies / water to the room. 
You cannot increase the temp past 27oC floor surface temp, but additional pipe will allow more energy to be input to the floor aka emitter. 

[Conor]

We did 100mm spacing in hallway as couldn't get great coverage due to pipes heading across it, staircase, matwell etc so had to make most of space available

[gravelrash]

Closer spacing means increasing volume of water which reduces boiler shunting on and off if gas or oil but then you fall into the issue of having a very low flow temp which is an issue if using anything else than Heat pumps