UFH and general heating system questions

[Wrt43]

First time self build for me, wish I had found this site sooner! I apologise if any of this has been answered already in depth, I’ve had a read about but still a few questions remain.

 

I have read  the posts on UFH here and just wanted to clarify what I’m doing sounds sensible. And looking ahead for the next 2 months I need to finalise the heating system design with the plumber.

 

House is part old, solid walls, single glazed sash windows, this totals circa 75 m2 split evenly between GF and FF. the extension is a further 65 m2, this is cavity walled with 75mm PIR insulation. The extension is all single storey. 

 

Floor or is the old house is 

1. breathable membrane

2. 150mm geocell glass aggregate

3. 100mm limecrete screed with UFH pipes in screed attached to plastic mesh.

 

Floor of new is

1. Compacted stone

2. Concrete oversight

3. DPM

4. 125mm PIR

5.. 100mm screed concrete with pipes in screed

 

 What I am unsure about is manifold position. I understand a central manifold is desirable but I’m really going to struggle to find a place to put it. I had planned for the manifold to be in the laundry, along with the TS, being fed from an outside boiler. However this is definitely off centre. I have attached a quick sketch of the place - distance from laundry to edge of zone 3 is 9m, going along the outside walls. I am concerned have a return from this will lead to a cold spot in the floor, and am unsure whether this is too longer run from the manifold. Zone 1 is old house, sitting room, zone 2 is kitchen / diner, zone 3 downstairs loo and bedroom/ensuite bathroom.

 

Secondly, the design of the heating system itself. DHW requirements will be 2 showers back to back in morning, then a bath / shower sometimes at the same time sometimes staggered in the evening. Then what I presume is typical usage for washing up etc.

 

What I’m unsure about from reading the posts here is

 

1. How does one judge whether an accumulator is necessary? Mains feed is fairly feeble but I haven’t measured it - is there a threshold requirement?

 

2. I was planning an external [ oil ] boiler, family always had Grants so would look for the same, thermal store to feed Rads on upstairs of old house, UFH through out ground of old and new, and then DHW. How does one spec a thermal store? By this I mean size, size of coil, immersion heater requirements?

 

3. I plan to install solar next year on the outbuildings, 10kw, and would like some guidance if possible on how to future proof the system to take advantage of this.

 

Thanks all

 

Bill

 

 

 

 

Edited February 26, 2018 by Nickfromwales
to add oil

[Tennentslager]

Bill welcome

Is zone 1, 75m over two floors (old building with single glazing) and all the rest 65m on one floor?

You're gonna need some expert advice I expect as this is a unique set up...

[Nickfromwales]

Welcome to the madhouse Bill. 

UFH gets laid to suit you mate so put the manifold where you like and pipe back to it accordingly. The trade off is having to run extra loops to the furthest zone to cover the same ares but without exceeding ( ideally ) 100m in length per loop. 

Panic ye not about cold spots from the returns, its not going to happen

22 minutes ago, Wrt43 said:

Floor of new is

1. Compacted stone

2. Concrete oversight

3. DPM

4. 125mm PIR

5.. 100mm screed concrete with pipes in screed

Why not reduced the concrete oversight, or do away with it altogether? I favour more insulation and more compacted stone, bearing in mind the reinforcing mesh for most here is in the upper screed with the ufh pipes zip-tied to it, killing a few birds with one stone. Id want a minimum of 150mm / 200mm of PIR under a heated floor. 

 

35 minutes ago, Wrt43 said:

3. I plan to install solar next year on the outbuildings, 10kw, and would like some guidance if possible on how to future proof the system to take advantage of this.

Solar thermal or solar PV please? More on the other heating / hot water stuff when we know that. 

 

36 minutes ago, Wrt43 said:

1. How does one judge whether an accumulator is necessary? Mains feed is fairly feeble but I haven’t measured it - is there a threshold requirement?

You need take a max static cold mains pressure reading over 24hrs, and also the litres per min flow rate at the outside tap. Fit a non return valve to the pressure gauge so whatever the peak reading is overnight will be left on the display. Critical survey criteria thats necessary before looking at an accumulator. 

 

[Wrt43]

Thanks both for replies.

 

Yes, the 75m2 is split evenly between two floors.

 

Nick, I wish I could change the oversight! Blame myself really because I didn’t put enough effort into finding resources like this forum before I started. 

 

I think I put 125mm of concrete down which whilst very useful to build off I can see is undermining the performance in the heating. Is there anything you would suggest to improve the performance of the floor - short of taking up the oversight, please don’t say that!

 

So to clarify all I have to do if I keep my manifold where I originally planned is to estimate the length of each run, if I’m over 100m I need to go off another port and do the remaining area with a separate loop. Do the pipes which are going some distance before they reach the desired location for heat need any additional insulation around them? Or is standard pipe work sufficient

 

The  other query is centres - friend of mine who has a similar set up,125mm PIR on oversight, did his at 250mm, though I’ve read 200 is the standard? I feel like there must be calculations I should be doing but don’t know where to look! If there are formulas for this stuff please point me in their direction!

 

Solar will be PV.

 

Thank you for tip re measuring mains pressure.

 

 

 

 

Edited February 27, 2018 by Wrt43

[Declan52]

You can get away with less screed depth to give you more insulation. A sand/cement based screed can be 75mm and one of the liquid screeds can be 50mm deep if you got one of them. Both options will help with the heat loss.

[Wrt43]

Thank you. 75mm gives me the space for 150mm of PIR.

 

I really wish I knew about EPS before I started. So much cheaper! Just have to use it on the next house!!

[Nickfromwales]

1 hour ago, Wrt43 said:

Thank you. 75mm gives me the space for 150mm of PIR.

 

I really wish I knew about EPS before I started. So much cheaper! Just have to use it on the next house!!

Cheaper, but poorer performing, so not necessarily a good alternative. However, if you put 250mm of it in, it'll be cheaper and not far off as good, overall. 

If you have the oversight then you have a structural subfloor. That indeed means you can go 75mm of dry sand / cement screed. Over the geocell, im not sure if you would still be safer reinforcing. 

 

1 hour ago, Wrt43 said:

So to clarify all I have to do if I keep my manifold where I originally planned is to estimate the length of each run, if I’m over 100m I need to go off another port and do the remaining area with a separate loop

Yup. You need to make the two loops the same length each so they dont go out of balance, eg one side of the room warms up sooner etc, ( or as close as you can get it ). You dont want 100m and 25m making up a 125m zone

 

1 hour ago, Wrt43 said:

Do the pipes which are going some distance before they reach the desired location for heat need any additional insulation around them? Or is standard pipe work sufficient

Lag the flow of the longest runs where they pass through other zones to get where they're going. Thisll also help stop overheating the floor where there are lots of pipes coming from the manifold

 

1 hour ago, Wrt43 said:

The  other query is centres

If going for thinner screed, go for tighter centres. Id go for 100 or 150, given that you can run slightly lower flow temps if you have more water volume in the floor. 

 

1 hour ago, Wrt43 said:

If there are formulas for this stuff please point me in their direction!

 

No formulas with me mate, im from the back streets   Just use the force, me. 

[Wrt43]

Thanks Nick for your help. I’m going to reinforce the limecrete floor as you say.

 

I was just thinking about the layout of the pipes today - can’t work out which way to go. Is there a standard method of arranging the pipes? My alternatives below.

 

 

[le-cerveau]

An example of spiral counterflow, the optimum.

 

 

Of your diagrams the first one is better, as it is counterflow, but you also want to spiral where possible.

[Triassic]

An interesting thread, I’m planning to lay UFH in my basement floor. The next question is where to buy long lengths of pipe? 

[PeterW]

23 minutes ago, Triassic said:

An interesting thread, I’m planning to lay UFH in my basement floor. The next question is where to buy long lengths of pipe? 

 

Usual suspects are WundaTrade and eBay ... and then you get into the PEX vs Pert discussion ..!

[Triassic]

Funnily enough, as soon as I started searching I was confronted with various sizes and material combinations...

 

Qual-pex 16 x 1.5mm

Pert-al-pert 25mm

Pex-al-pex 16 x 2mm

Pert-al-pert 20 x 2mm

Pert-al-pert 18mm

Pert-al-pert 12mm

 

WARAS approved or British Standard?

 

In the past I’ve bought too much and used the leftovers for general hot and cold water plumbing.

 

So what would fellow self builders and Nick suggest?

Edited March 1, 2018 by Triassic

[PeterW]

16mm doesn’t fit into ordinary fittings without using connectors that pretty much negate the cost saving of using up bits that are left. 

 

I’ve used Pert-Al-Pert from Wunda - I used loopcad to do the design then bought reels based on the cutting list it provides. Was pretty accurate too. 

[Alexphd1]

Just now, PeterW said:

16mm doesn’t fit into ordinary fittings without using connectors that pretty much negate the cost saving of using up bits that are left. 

 

I’ve used Pert-Al-Pert from Wunda - I used loopcad to do the design then bought reels based on the cutting list it provides. Was pretty accurate too. 

 

Keep a eye on eBay for these fitting. I picked up 80x maincor 16mm mlcp to 15mm compression adaptors for £10 in a auction. I am pretty sure the maincor pipe comes out same factory as uponor which we used on every job for 15 years without 1 leak.

[Triassic]

2 minutes ago, PeterW said:

used loopcad to do the design then bought reels based on the cutting list it provides. Was pretty accurate too. 

 

That was going to be my next question, do I need a design or can I simply fit the pipe as per the diagram above.

[le-cerveau]

You can use loopcad free for a month so time when you download it.

You can pretty much use your own logic to work out the best runs as loopcad will manage simple square rooms but anything more complex (round bathtub and toilet...) and it gets a but suspect and you end up manually drawing the loops anyway.  

It will give you the lengths though.

[PeterW]

Loopcad can be downloaded and used free for 30 days. It allows you to work out heat loss and also temperature for flow plus the spacing needed. Mine has 3 different loop spacings dependent on the location and the heat required to go with a consistent flow temperature. The downside is that it is a US programme so you need to do some conversion to get the right values for insulation etc. 

[Triassic]

Ok I have to ask, why is UFH pipe 16mm and ordinary water pipe 15mm. To have two sizes so close looks like nothing than a sceptical marketing ploy, not very sustainable, given you then need two sets of fittings!

 

I for one will be buying the 15mm and use any leftovers for general plumping jobs?

Edited April 7, 2018 by Triassic