50mm pipe spacings in problem rooms - any bad effects?

[James of the North]

Yo! Accoring to LoopCAD we are struggling in a couple of rooms to achieve required load with our params (flow temp, heat loss, floor covering etc.). For example, a side extension with 3 out of 4 rooms glazed floor to ceiling, and kitchen with a smaller floor area due to cabinets and penisular on 3.5 walls.

 

I've not been able to find out much about running at 50mm pipe spacings, and I would only do it in these very limited situations (trying to avoid supplemental heating), and use regular pipe spacings in the rest of the rooms.

 

Are there any bad effects of doing this, other than the extra cost of an extra circuit (pipe and more manifold ports)?

 

For example heat short circuiting from the flow to the return due to the closer proximity? Floor not taking the heat as easily or quickly when so much heat presented to it?

 

I've seen photos of UFH pipework where for limited distances, like transition runs, or around the outsides of rooms, people run pipes almost touching (just the pipe staples preventing them from touching), and not sleeved, or, at 50mm pipe spacings when using the egg crate type panels, so this suggests there aren't any 'bad effects' for the heated floor area of floor covering above?

 

More heat in the floor due to closer spacings = more heat output into the room?

 

Anyone any experience of 50mm pipe spacings in limited situations (even just on lenghty transition runs - can you notice a difference compare to standard pipe spacings)?

 

Retrofit, not PH & gas boiler not HP.

 

James the Red Engine

[JohnMo]

If you need 50mm spacing I would go back to basics and see what you have done wrong. Increase flow temp, change floor coving. Are you sure you have insulation values correct?

[James of the North]

I'm genuninely curious to know if there are any negatives other than those I outlined (cost, etc.) for 50mm spacings.

 

Thanks

[BotusBuild]

James,

John's suggestion to double/triple check your workings is a sound one.

 

How big is this room? Do you know what the heat loss is for the room? What solar gain are you going to get if three sides are glazed floor to ceiling?

[Conor]

At 50mm spacing your bend radius will be really tight and tough to achieve in some places. You'll need to increase spacing to 100mm at room edges / corners to make it doable.

 

But as above, something fundamentally wrong if you need 50mm pipe spacing. To modern standards, 200mm, or worst case 100mm, would be standard.

[JohnMo]

You just need to look at the practicality of installing. It's been done, but by overlapping various loops, so more like a 100mm or something spacing then a second loop straddling the first. Little bit of a pain to do, but doable. But why, are you trying to flow stupid low flow temperature, that may not even be practical to run? If sounds wrong it normally is 

 

What depth of screed are you using?

 

Our room with the most loops is fully glazed one end, 6m tall fully vaulted and we can manage on 300mm centres and we have to heat down to -9 on a regular basis.

[marshian]

1 hour ago, James of the North said:

Retrofit, not PH & gas boiler not HP.

simple questions from me what gas boiler, what’s it min modulation rate and what flow temp are you targeting from the boiler?

why am I asking this?

 

I’m using a gas boiler on weather comp with only rads (13 with 135 litres of circuit volume) no UFH. House has a heat loss of 4kW at -2.5 deg C 
 

At 10 Deg OAT the boiler target is 23 Deg C and at -5 Deg OAT the boiler target flow temp is 36 Deg C (we don’t see that OAT very often)

 

For all the Viessmann boilers good points it struggles to not overshoot at the 10 Deg OAT flow rate and I think a practical min is probably closer to 28 Deg C but it has a neat party trick that helps to reduce cycling so I’m comfortable with the level of cycling in the shoulder season.

 

Boiler is a Viessmann “Heat Only” 16 kW range rated to 4.0 kW however has been set up with DHWP so RR is ignored for HW

 

My previous boiler practical min flow temp was 45 Deg C with a 10 kW min output

 

 

[James of the North]

13 hours ago, Conor said:

At 50mm spacing your bend radius will be really tight and tough to achieve in some places. You'll need to increase spacing to 100mm at room edges / corners to make it doable.

 

But as above, something fundamentally wrong if you need 50mm pipe spacing. To modern standards, 200mm, or worst case 100mm, would be standard.

 

The bend radius is the same for 50mm pipe spacings on 90 degree corners, as it is for any other pipe spacing, which is the bulk of a sprial counterflow circuit. It's only in the middle you have to revert to 150mm spacing to create one or two 180 degree returns.

[JohnMo]

What flow temp are you trying to achieve that needs 50mm centres?

[James of the North]

Here's some examples of masses of transition pipes at 50mm spacings, NOT sleeved.

 

Must result in over heated areas above 27 to 29 degrees if the flow temps are set to achieve 27 to 29 in the rooms they are going to?

 

Is my assumption correct, that if a flow temp and flow rate for a particular circuit to achieve a floor surface temp (top of screed) of N degrees (27, 29 etc.), then bunching up a load of transition pipes together with closer spacing, will result in a higher floor surface temperature? LoopCAD doesn't seem to model this; looks like it creates an 'average' floor temp (can't see an analysis view for hot spots 🥵)

 

What about short-circuiting from flow to returns, at what is the extremeity of the circuit (hottest part of the flow, coolest part of the return)?

 

I can't see how the floor temperature can be controlled in these areas 🥵. Surely will lead to much higher floor surface temperature, for whatever floor covering is going above (tile or brick slips would be fine, but carpet, wood etc.

Edited September 5 by James of the North

[Mike]

2 hours ago, James of the North said:

Surely will lead to much higher floor surface temperature

The temperature will be limited by the water temperature supplied, so it will just reach the maximum temperature of 27 to 29 quicker - it can't go higher than that.

 

2 hours ago, James of the North said:

What about short-circuiting from flow to returns

No problem; the hot water is still being pushed through the pipes, so the floor will warm up.

[JohnMo]

Depends on a number of factors, screed thickness being one.

 

Wide pipe spacings give a ripple temperature across the floor, the closer the spacing the smaller this ripple becomes. The floor loop pipes emit heat radially, the wider the spacing the more the heat is diluted before getting to the surface where it is used to heat the room. But reducing that ripple is in the form of diminishing returns. And when running low temperature UFH cannot be felt.

 

Examples 100mm screed, with 18mm oak floor covering

for 20W/m2, on 300mm spacing you need a flow temp of 30 degs

For 23W/m2 on 300mm spacing you need a flow temp of 31 degs

 

Same conditions but 50mm centres, you drop the flow temp by about 2 degs, so 28 and 29 for the above outputs.

 

For every m2 300mm centres has about 3.3m of pipe, while 50mm has circa 20m.

 

Our 192m house has a loose 300mm spacing and 7 loops in total. Moving to 50mm centres would increase the number of loops to about 40, so 4 or more manifold instead of one. ASHP circulation pump would require several other pumps to supplement it.  The gain in efficiency from boiler or heat pump would be spent on stupid amounts of pipe, pumps to buy and run for ever more.

 

LoopCad does analyse the bunched pipes, our utility showed a huge overheat just by transiting pipes, I added insulation to the flow pipes the overheat went away.

 

If you can't do the floor at 150mm centres your target parameters are wrong - increase flow temp, sort the design for your worst room first, then it is easy to sort the balance of the house, with wider spacings if needed, to get a balance output in all areas.

[James of the North]

On 05/09/2025 at 22:20, JohnMo said:

LoopCad does analyse the bunched pipes, our utility showed a huge overheat just by transiting pipes, I added insulation to the flow pipes the overheat went away.

If you had a 4m wide room, with a bunch of transition pipes at one side only, LoopCAD does not highlight that as being a hot spot - all it does is show an average floor surface temperature for the entire floor (in that view). Beyond some distance (say 1m) from the bunch of transition pipes, there won't be any increased floor surface temp due to the transition pipes. I don't think the average for the floor would be correct either.

[James of the North]

On 05/09/2025 at 21:25, Mike said:

The temperature will be limited by the water temperature supplied, so it will just reach the maximum temperature of 27 to 29 quicker - it can't go higher than that.

I disagree. If the flow temperature was say 40 degrees, what is to stop the floor surface temp increasing way beyond 27 to 29, where you have very close pipes in transition? The rest of the room where you have normal pipe spacings, yes, you design the flow rate to ensure 27 to 29 degrees, so an area of floor with much closer pipe spacing would lead to a higher surface temp. In this type of situation you essentially have two different set of parameters, which will ulitmately lead to two different floor surface temperatures.

[jfb]

How hot do you want your house?
in my experience the thermostat level needed for a house with Ufh is less than one with radiators. 

[JohnMo]

25 minutes ago, James of the North said:

If you had a 4m wide room, with a bunch of transition pipes at one side only,

No idea what you are trying to ask?

 

You seem to ask one thing then if you get answer you don't want you go on a tangent. You only do tight transit through room if you are running multiple zones, otherwise you would use the pipes spaced where possible to utilise the heat before getting to the end destination. Make the pipe work for its cost. Only room I have transition pipes in the utility, because manifold is there. Hallway, main bathroom are all heated by using pipes going somewhere else, suitably spaced to match heat required.

 

Original ask was can I do 50mm spacing because you cannot achieve heat output any other way. Now you are talking transition through rooms?

 

If you answer the simple questions asked, you may get some sensible answers, until then I will watch but not answer anything further.

[James of the North]

51 minutes ago, JohnMo said:

Original ask was can I do 50mm spacing because you cannot achieve heat output any other way. Now you are talking transition through rooms?

Yes, as an example of 50mm pipe spacings, which you see regularly on photos of UFH installations online, and their impact.

[James of the North]

53 minutes ago, JohnMo said:

No idea what you are trying to ask?

I was responding to your claim that LoopCAD does model what I said it doesn't model. Keep up 😜

[James of the North]

54 minutes ago, JohnMo said:

If you answer the simple questions asked, you may get some sensible answers, until then I will watch but not answer anything further.

I don't think you have any experience on 50mm pipe spacings. It appears you have done one install, on 300mm pipe spacings, using a totally different heat source and flow temperate to mine.

[marshian]

Still interested in the Gas Boiler being used because if you are modelling heat ouputs from the floor based on a boiler flow temp (no mixers or blending) you might find that quite difficult - if you have got a boiler that will do low flow temps and weather compensation then if you are all UFH then you’ve no need to mix or blend and circuit control becomes much simpler - just flow rate changes through the circuits to balance the heat output required

[jfb]

58 minutes ago, James of the North said:

don't think you have any experience on 50mm pipe spacings. It appears you have done one install, on 300mm pipe spacings, using a totally different heat source and flow temperate to mine.

Good way to keep anyone who has responded on your side!

 

have you ever installed Ufh?

[-rick-]

@James of the North I appears there is a disconnect between what you are asking and the answers you are getting. I want to try an explain why and hope that in doing so will help you get the best value from this forum.

 

Based on your questions you clearly have some knowledge of ufh systems and have done most of the design work already. I think you came here wanting some very specific questions answered and are not really getting those questions answered in the way you want. The reason for this is that your questions imply you have a situation that is far outside what is normally required and the first thought of many of us here is that there must be something wrong in the assumptions that lead to your questions.

 

This forum has a long history of people coming with questions like this that after some back and forth prove to be based on either mistakes or misunderstandings at the design phase and after further work the result is a system that is fairly different from the starting point. It may be that your calcs are all correct and you indeed do have a very unusual situation but if you want to get full engagement and value from this forum help us understand that. Show us your design, floor plans, heat loss calculations, answer questions even if they don't seem valid to you. It will take some back and forth but either someone will point out a mistake/misunderstanding that leads to a different design or you will get people fully engaged in helping you get the best result.

[Mike]

On 07/09/2025 at 12:10, James of the North said:

I disagree. If the flow temperature was say 40 degrees, what is to stop the floor surface temp increasing way beyond 27 to 29, where you have very close pipes in transition?

Because @James of the North is asking about increasing pipe spacing in specific rooms, not 50mm pipe spacing near the manifold (where a somewhat higher temperature would occur).