Underfloor heating choice/potential

[Deluks]

Background: Just lifting up my kitchen floor tiles at the moment, was gonna self level/liquid dpm/10mm insulation board/electric warmup matting/tile n grout.

However after seeing the state of the concrete underneath...lots of brittle sandy patches, and a hole where a worm popped his head through before ducking down again, I'm tempted to dig the lot up, 70mm kspan/3" screed or concrete and then heatmat/tile.

But would I be better off sticking some pex UFH in the screed instead? We're only talking about 3m maximum area here, and there's a rad in the living room on the other side of the kitchen wall that I could nick the hot water from.

Seems expensive but this kit got me thinking...

http://www.underfloorheating1.co.uk/product/Single_Room_Thermostatic_Valve_Kit_Danf

Would it really be as simple as taking the hot water from the rad, through the wall and into the screed?

...and can I diy a kit like this myself for less money? I have about 30m of new 15mm pex sitting in the garage gathering dust.

 

[theoldun]

Sugsgest you read, Hypocaust, Latin for Ancient Roman Underfloor Central Heating Systems. This will be right up your street, you can use those two Scyamore trees for fuel. Should last yer for five years.
By the way, I'm in the market for a bren gun carrier, if you hava one of them gathering dust in the garage.
old un.

 

[mointainwalker]

You don't need to buy a kit for what you are suggesting and since you have the pipe in the garage it will cost you next to nothing since the area is so small.

The only real question is : do you actually want to heat this space or "just take the chill off".

This will determine how much pipe you lay, but for that you need to do a heat-loss calculation. What is heating the area at the moment ?

oldun - did you bring up the Bren carrier because of the recently-passed date or your times in Lympstone ?

 

[Deluks]

The room only gets heated when I open the oven to get my pizza out.
Using the kitchen in winter, ones feet are like blocks of ice within 20 mins. 25 mins if I'm wearing slippers.

Only really need to take the chill off the floor as the air in the room itself doesn't get noticably cold.

So 70mm of celly with some pipe in the concrete cover should certainly warm the floor up. But it's the whole hassle of connecting it up, Ok not so much hassle but more that I haven't a clue what bits I need or how much it will set me back.

Old 'Un: sorry no bren gun carrier, but I've got a few .303 ammo boxes you can keep your link in. I wouldn't want you to get low on rounds when you're chasing up those non-payers!

 

[mointainwalker]

A normal UFH system will give you around 10W/linear metre @ 40 C.

Therefore your rad feed at 65-70 C will give 16 -17 W per lm.

If you just want to warm your toes as you suggest, just wind in 20 lm of your buckshee pipe (assuming you mean 3 m2) and it will be warmer. Use all the 30 lm and it will be warmer still.

Obviously you will will need to think about a heat-loss further along the same circuit.

As for "hassle" connecting pipes , just copper to PEX connectors. They don't give them away , but 100 times cheaper than electric mats you initially spoke of.

And don't forget the underground insulation you already mentioned.

 

[ajrobb]

http://www.gasapplianceguide.co.uk/Underfloor Heating.htm and FAQ
How can water in an underfloor heating system work at a cooler temperature than the radiators in the rest of the house in a mixed wet system?

 

[Deluks]

OK, been having a google.

So all I'll be doing is extending the pipework between 2 rads. (No much different from adding another rad into the circuit ??) This will obviously affect the heat up time of the next rad in the chain, but considering it's only for a few metres of pipe ??


The previously mentioned rad in the adjoining living room, has it's send/return pipes coming down from upstairs, and are conveniently accessible from a cupboard in the hallway, which is also right next to the kitchen. Suppose I could simply attach a 2 way manifold to the return from living room rad and run the pipe through and under the wall into the kitchen ??

AJ, your link goes on about room stats, actuators and the like. Could I dispense with all this and just accept that the ufh will always be working whenever the house rads are on ?? (ie: when it's cold!)
Would it be possible/sensible to add a TRV in there at all, or wrong tool for the job? ??

Manual control: What would be the best way the isolate the system in the case of a leak ?? (unlikely I know but...?)

Yays or nays to all the 'red question marks' from those in the know (please)

 

[mointainwalker]

So all I'll be doing is extending the pipework between 2 rads. (No much different from adding another rad into the circuit ??)

Correct.

This will obviously affect the heat up time of the next rad in the chain, but considering it's only for a few metres of pipe ??

Don't forget it's also a couple of hundred kg of concrete as well

The previously mentioned rad in the adjoining living room, has it's send/return pipes coming down from upstairs, and are conveniently accessible from a cupboard in the hallway, which is also right next to the kitchen. Suppose I could simply attach a 2 way manifold to the return from living room rad and run the pipe through and under the wall into the kitchen ??

Unsure exactly what you envisage as a manifold here, but why not treat just as a radiator as you said before and just re-route the return through the floor, then just need a connector.

AJ, your link goes on about room stats, actuators and the like. Could I dispense with all this and just accept that the ufh will always be working whenever the house rads are on ?? (ie: when it's cold!)
.
Would it be possible/sensible to add a TRV in there at all, or wrong tool for the job? ??

Silly in my view to throw the whole armada of controls at it when it is such a small area and you initially mentioned cost as a factor. just let your existing controls monitor it.

 

[Deluks]

Not quite sure about manifolds myself.

I envisaged some thing like this:

Connecting this into the straight pipe that runs through the cupboard, then just lay and 'plug in' the pex.

Do these manifolds 'redirect' the existing flow or does the hot water simultaneously flow the the existing pipe AND through the manifold


Or to put it another way, is the manifold 'sealed off' between the two valves (so if I shut off one of the valves then I interrupt the return flow back to the boiler?)

Appreciating the input.

 

[ajrobb]

AJ, your link goes on about room stats, actuators and the like. Could I dispense with all this and just accept that the ufh will always be working whenever the house rads are on ?? (ie: when it's cold!)
Would it be possible/sensible to add a TRV in there at all, or wrong tool for the job? ??

I think you might be confusing me with someone who knows what they are talking about.

My understanding is that the underfloor heating can end up with loads of gubbins - pump, mixers etc. The manifold sounds quite complicated as it can mix feed water with return water to maintain the correct temperature. If you just want to make the UFH part of the return circuit, I wonder if you could just include a couple of check valves and a by-pass valve so that you can isolate and balance the UFH? The amount of water will depend on the radiators upstream.

One problem is that the extra thermal inertia of the floor will give different characteristics to the kitchen heating (cold in the morning and baking in the evening) compared to the radiators. However, you sound fairly flexible about the temperature of the kitchen and it might be OK to compromise on cool air with a comfortable floor in the mornings and cosy warmth by the end of the day.

 

[mointainwalker]

If you want peace of mind, go with the check valves.

When laying you will also need something to fix the PEX to as it is impossible to control .

You can buy the pre-moulded insulation blocks with the bollards on to wrap pipe around, but they are very expensive. I suggest normal sheet insulation and then a panel of small diameter ( 3 mm ? welded-mesh on top to wire the pipe to. Don't wire the pipe tightly to the mesh as this could risk cutting the pipe when heat causes it to expand.

The mesh squares help with the spacing as well.

Let us know if you go ahead as this question arises from time-to-time but I have never seen a comment after it has been completed.

 

[ajrobb]

Would it be possible/sensible to add a TRV in there at all, or wrong tool for the job?

I don't think you want to throttle the flow through the return from upstream radiators. However, you already have a radiator in the kitchen. You could keep that with a TRV to top up the UFH.

How many of the upstream radiators have TRVs? The returns from them get throttled and cold once the house is warm. You might want to be a bit canny about running the UFH pipe first to areas that need it most.

I can see that a full-blown UFH system would need to keep flow rates up with an additional pump and recirculate water through the floor pipes to reduce the temperature drop so the floor heats evenly. I imagine the manifold will have 3 inlets

• warm radiator return
  cool UFH return
  controlled hot feed

I suspect the hot feed is controlled to maintain the manifold temperature at 40°C. I imagine it has 2 outlets

• UFH pump inlet
  boiler return

 

[Deluks]

Mountain: I was thinking of using the plastic staples pushed into the insulation, to hold the pipe. However your plan would enable me to fix the pipe in the centre of the slab, so the heat won't have so far to travel to reach the floor surface.
I could use some A142 fabric in the concrete and fix the pipe to that, although not so sure about having, metal, concrete and plastic all right next to each other with all the heating and cooling that's going on. Suppose I could 'tether' the pipe using stiff wire so that it sits about an inch or so above the fabric. Will probably have to up the slab to about 120mm or so to allow for decent coverage top and bottom.

AJ: You have convinced/confused me enough to dispense with the gubbins, I'll keep it simple.

Keep at it lads, most helpful

Anyone else following and wants to chip in?

 

[mointainwalker]

Haven't used staples myself because I have read that they can tear out and having wrestled with the tubing trying to get it into position I can well believe it.

I did a lot of research before laying my floors and it was gerally agreed that 10 mm off the insulation should be enough to allow you to tamp the screed beneath it. I just put bits of stone under the crosses of the mesh.

60 -70 mm is regarded as the normal screed thickness but you are only trying to warm your toes so do as you like. I think the only professional rule is a minimum of 30 mm over the pipes.

 

[Deluks]

I'm hoping do do this within the main concrete slab and finish off with a couple of bags of self levelling for the tiles to go on. Don't know if that's wise or not?

mot/blinding/dpm/inso/concrete/slc/tiles. Certainly an improvement on the crap that I've just dug out!

1) Will concrete affect the pipe in any way.
2) Will the laying of pipe in the main slab weaken the concrete in any way? (I doubt it due to the extra inch or so of coverage and the mesh)
Only taking floor cabs and appliances so no big deal.