Underfloor heating

Agile · 31 Aug 2010

Electric heating is very expensive compared with mains gas.

The reason the UHF pipe loses heat is that its job is to do just that and to lose its heat and give it up to the floor.

Rads assume a flow of 70° and a return of 50° to operate with a condensing boiler most efficiency and to give out close to the rated heat output.

You would need rads at least twice as big if you wanted a flow temperature of 50°.

Any pipe will lose heat but to do that most efficiently and get 100w/m² you do need to install it in the normal way, ideally with the pipes burried in concrete or at least having metal spreader plates.

Dont expect plumbers to be pulling the wool over your eyes. Their skill levels will vary but thats the same in amy profession.

Tony

DeltaT · 31 Aug 2010

The maximum loop lenth is kept to 90M max, this will enable you to use a standard 5 or 6M head circulator on a manifold with up to 5 loops.

You have got to address the problem of the heat-loss calcs mate, as everyone thinks the details you have are wrong. The design is very, very important if the system is to work.

deuce22 · 31 Aug 2010

Hi DeltaT.

Can you advise me on how to rectify the calculations.

Is there a more realistic calculator on the net.

Thanks.

deuce22 · 31 Aug 2010

I've just run another online calculator and it has come back with 5500 watts.

4000 less than the other one.

DeltaT · 31 Aug 2010

Have you taken out any losses through the floor & any air changes from your calcs??

looneyfitter · 31 Aug 2010

HI there, i have just came home from work so not had time to read all comments. I am however P155ed with mointain walkers comments!!!!!!

I will add my comments later on after tea. I in general go off a detailed plan provided by whomever i decided to purchace my materials off when it comes to fitting out.

I am merely giving a user on here some advice with regards to a tried and tested method of overlay at my OWN home. I HAVE HAD NO ISSUES what so ever and all works well.

My 1st floor construction is basically

1) fibre glass lagging between joists from new build

2) 18mm board,

3) Foil insulation (yes i know there should be a 25mm gap) Theres 9 inches so it happens to your plasterboard celing below!!!! Heat rises did you know?

4) 15mm pipes run appro 120-150 centres (150 in general)

5) 18mm batton between 2 loops

6) Kilndried sand between the battons (perfect conductor)

7) 15mm engineered ply screwed to the battons.

8) Flow temp of 35-40 deg (iirc)

All works sweet as a nut!!!

As for down stairs There is already (usually depending on age of build) 100mm kingspan in the floor so whay would you want to re-add it again at floor level? I used the foil purely for added comfort because i could and a little more radiant effect.

As for pipe length runs..... Ok i may have not eplained enough for YOU to understand however other engineers like Agile DID.

Pipe runs/heat loss are all relative......

Biggles.. · 31 Aug 2010

heat calc is 35W/sqM
cooling calc is 100W/sqM

other rough guides are 5btu/cuFt

a 6Malpha will happily run 12 zones at 100M loop length.

you have to remember how the pump operates betwenn flow and return rails of a manifold.

deuce22 · 31 Aug 2010

Hi.

I had my uncle over today (who has built a few houses over the years) to give me some advice and he agrees that U/F heating is the way to go.

He said that a lot of heat from the radiators will be circulating above us due to the ceiling height.

He did mention about screeding the floor after the pipes are fixed, but after looking at the cost it will be to much for me.

I think that doing a similar set up as looneyfitter is the way for me to go.

Looneyfitter.

If the existing floor is a concrete slab would putting foil underneath be sufficient.

I would then do the exact same thing, fitting batten, ply and filling it with sand.

What lengths of pipe did you use per zone and what manifold did you use.

Thanks.

DeltaT · 31 Aug 2010

lcgs said:
heat calc is 35W/sqM
cooling calc is 100W/sqM

other rough guides are 5btu/cuFt

a 6Malpha will happily run 12 zones at 100M loop length.

you have to remember how the pump operates betwenn flow and return rails of a manifold.

35W/M2? Can you please confirm what this figure is? Did you do a heat-loss calc from the details the OP gave you? If so what mean water temp. Is that floor output based on?

With the greatest respect, I've seen 6M head circulators on manifold as you discribe & frankly it will strugle doing that.

Any manifold with more than 5 loops we would always cross connect, this will improve the circulation & make the balancing easier.

looneyfitter · 31 Aug 2010

HI Delta what do you mean by cross connecting?

DeltaT · 31 Aug 2010

looneyfitter said:
HI Delta what do you mean by cross connecting?

Hi mate, what that means is 1st Flow is the last Return on the manifold. Much, much easier to balance the system when you do it. Never ever used an Alpha circulator either & never ever 'dead headed' a circulator yet.

But each to their own, whatever works for you.

I've been on jobs where half the pipes were missed out in a concrete screed (DaftyDIYer) & with careful set-up of mean water temperatures it'll work very well!! Of course it would be daft doing something like that, design & correct installation is vital.

looneyfitter · 31 Aug 2010

Deuce how old is the house? To be honest if it has a concrete slab then the chances are it will have insulation. I would be drilling a test hole to check tho. Best to use a 2 "core drill, or a 25mm sds concrete bit. Be careful as you get to 100mm tho as if it has no insulation you will be hitting you DPM around that depth.

If you have insulation then i feel you will be happy days with my method. I would try and get your centers at 100mm as oposed to my 150mm tho as my house is fairly new and very well insulated. 100lm will be good for 10m2

As said i would use set back timers with a manifold. The mainifold i use is an emmeti on (spelling) quite a nice pieco of kit.

Be sure to insulate around your skirting perimiter.

looneyfitter · 31 Aug 2010

DeltaT said:
looneyfitter said:

HI Delta what do you mean by cross connecting?

Click to expand...

Hi mate, what that means is 1st Flow is the last Return on the manifold. Much, much easier to balance the system when you do it.

Lost me there sorry matey. So where you have your flow manifold say on top and your return manifold on the bottom with each flow and return usually above and below you would fit say the 1st circuit flow at the top but its return say last on the right?

Sorry if i dont get it. I am far from an e pert at UFH but know the principles.

Gareth

looneyfitter · 31 Aug 2010

deuce here is a basic design layout similiar to what i have done but obviously above the floor

deuce22 · 31 Aug 2010

Hi looneyfitter.

Can you confirm if I'm on the right tracks here.

If I have insulation in the concrete I can fix the pipe directly onto it at 100mm centres.

Fix batten in between each pipe and then fill voids with sand.

Fix ply board sheets and then the laminate flooring.

Would I need to use the under felt for the laminate.

Thanks.

diynot

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Underfloor heating

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