Could you give some feedback on this UFH design?

[Bancroft]

Hi all,

 

I'm looking for some feedback on an underfloor heating design.

 

I had someone do a layout for UFH pipework for our single storey, 211sq m, new build and I’m looking for people with more experience than me to look it over to see if it makes sense.

 

They have split the whole system into two manifold areas – manifold 1 one in the lobby to the shared bathroom, and manifold 2 in the pantry.

 

They have then put more individual circuits (10 v 😎 on to manifold 2 which results in the guest bedroom (left hand end of the building) being on a different manifold to the other bedrooms.

 

This also means a lot of pipework squeezing through the door to the pantry and, presumably, additional heating in the pantry area that would ideally be kept cooler.

 

Ideally, we’d be looking at a maximum of two heating zones – the bedroom side of the house and the living side of the house.

 

My thoughts/questions are:

 

Twelve ports looks like the max size for a single manifold so we’re probably going to need two as a minimum.  But, are there any advantages/disadvantages to going to three to relieve pipework runs/reduce pipe lengths?

 

Would it not make more sense to put the bigger manifold in the bathroom lobby area, instead of the pantry?  That would mean fewer pipes having to go out through the door to the hall as some circuits are within the central bedrooms and bathroom.  It might also reduce overheating in the pantry.

 

It would also mean that the A1/A2 circuits to the guest bedroom would then be on the same manifold as the other bedrooms.

 

Finally, is there a height limit at which manifolds can be mounted?  We’re going to have a warm loft and I’m just wondering if manifolds could be mounted In the loft – at about 3000mm above finished floor level –  and still operate?

 

Grateful for any feedback on the above or any other errors/omissions/improvements can you see from the layout.

[JohnMo]

To give you some idea on my thoughts

 

Our house is single storey 192m² and have 600m of pipe in floor at 300mm centres and covering about 160m². Our max ASHP flow temp is 32 at -9.

 

Your design relies thermostats to control room temperature. Your design needs to be room balanced. But like choosing a correct size radiators by room heat loss.

 

That plan sells you lots of stuff.

 

 

[Mr Punter]

You have about a mile of pipe in the floor.  I don't like it when the runs back to manifold are tightly spaced.  Can any of the pipes go under the walls?

[Bancroft]

2 hours ago, JohnMo said:

600m of pipe in floor at 300mm centres

Did you come to the 300mm centres through your own calculations or a plumber/UFH engineer?

 

The design we have follows a more common (it appears) 150mm spacing.

[Bancroft]

1 hour ago, Mr Punter said:

Can any of the pipes go under the walls?

General consensus seems to be to NOT put pipes under walls.  Presumably that's in case pipes need maintenance/repair later but as they're in screed it seems a bit of a moot point.

 

Also, if putting into screed (as opposed to slab foundation) most of the walls would most likely be in place by the time it comes around to laying out UFH pipework.

 

I do agree, though, that doorways etc create tight runs which is one of the reasons why I was asking about multiple manifolds in order to spread the load.

[JohnMo]

24 minutes ago, Bancroft said:

Did you come to the 300mm centres through your own calculations or a plumber/UFH engineer?

 

The design we have follows a more common (it appears) 150mm spacing.

I used LoopCad to model house, then balanced room by room output so no supplementary heat was needed or I wasn't over heating rooms. They have used LoopCad to model house put omitted to balance heat output.

 

I need about 3kW heat output at design conditions to heat whole house. My hall uses loops transiting though it to heat the area, by spacing them through the hallway. Did same with utility (manifold location) but some loops required to be insulated so as not to over heat room.

 

150mm provides a quicker response time, and maybe a degree or so cooler flow temperature. But if doing WC or batch charging floor that doesn't really matter.

 

The compromise position is to do enough loops to get away with one manifold and have enough flow capacity within the ASHP circulation pump so you don't need a second circulation pump. 30 to 40W to drive second pump doesn't sound much, but will drop a will likely cost you £30 to £40 a year to run doing heating only. Double that if you do cooling.

 

Entrance hall has a dedicated loop, plus it has 4 other loops passing through it. Space the 4 loops out across the hall and you have deleted 1 loop.

 

Space ensuite and bathroom at 100 to 150mm centres - you cannot have enough heat in those rooms. Rest of the rooms in 200 to 300mm spacings.

 

A mean flow temp of 30 degs, on 150mm centres will output 40W/m² so your living kitchen looks to be 6x8m so area is 48m² so you are putting about about 2kW into floor on your design day. That floor comprises 5 loops and about 400m of pipe. At 300mm centres same flow temperature you are putting 25W/m² or 1.2kW, which maybe more than you need. You then can do 2 loops and 200m of pipe. Saving 3 loops. Do a similar exercise with each room. Design sheet to assist, attached. The attached doesn't include floor covering tog rating.

 

 

 

 

[Bancroft]

On 27/08/2025 at 14:53, JohnMo said:

I used LoopCad to model house, then balanced room by room output so no supplementary heat was needed or I wasn't over heating rooms. They have used LoopCad to model house put omitted to balance heat output.

 

I need about 3kW heat output at design conditions to heat whole house. My hall uses loops transiting though it to heat the area, by spacing them through the hallway. Did same with utility (manifold location) but some loops required to be insulated so as not to over heat room.

 

150mm provides a quicker response time, and maybe a degree or so cooler flow temperature. But if doing WC or batch charging floor that doesn't really matter.

 

The compromise position is to do enough loops to get away with one manifold and have enough flow capacity within the ASHP circulation pump so you don't need a second circulation pump. 30 to 40W to drive second pump doesn't sound much, but will drop a will likely cost you £30 to £40 a year to run doing heating only. Double that if you do cooling.

 

Entrance hall has a dedicated loop, plus it has 4 other loops passing through it. Space the 4 loops out across the hall and you have deleted 1 loop.

 

Space ensuite and bathroom at 100 to 150mm centres - you cannot have enough heat in those rooms. Rest of the rooms in 200 to 300mm spacings.

 

A mean flow temp of 30 degs, on 150mm centres will output 40W/m² so your living kitchen looks to be 6x8m so area is 48m² so you are putting about about 2kW into floor on your design day. That floor comprises 5 loops and about 400m of pipe. At 300mm centres same flow temperature you are putting 25W/m² or 1.2kW, which maybe more than you need. You then can do 2 loops and 200m of pipe. Saving 3 loops. Do a similar exercise with each room. Design sheet to assist, attached. The attached doesn't include floor covering tog rating.

Some really useful information here, thank you.

 

I did start to look at Loopcad but my brain just said no; I may need to go back and review because this seems like one of those things that the phrase 'If you want something doing properly, do it yourself' applies.

 

I like the principle of paring back the number of loops and also the widening of centres to 300mm to reduce both the number of manifolds and also the amount of pipework.  I'm not so worried about response time as I expect the system will essentially be on for winter and off for summer.

 

More work needed from me but thanks for the direction and guidance.

[JohnMo]

11 minutes ago, Bancroft said:

I'm not so worried about response time as I expect the system will essentially be on for winter and off for summer.

I do cooling (UFH) all summer until about October (weather dependent) then flick the switch to heat. As I am on the cusp of heat or cool, when I swop over the ASHP may run a few hours until it gets the slab where it wants then Weather compensation takes over, then it will just blib heat in as needed. The floor although slow, is as quick as the house when you and running at temperature response. If running WC you really don't need a responsive floor, start heating and leave it well alone, no thermostats are needed, just run nice low flow temperatures. My WC curve is something like 

 

25 flow at 20 degs

32 flow at -9. Heating doesn't actually start to kick in until outside is about 10 degs average.