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Underfloor heating system design?

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johntheplumb

Gas Engineer
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Last week I installed UNF heating in a concrete base for a new build house. The seize of the house is 330m2. The total pipe run in the base was 1150m with 3 manifolds. I'm expecting to to run around another 850m for the 1st floor with 2 manifold. There is 200mm foil back insulation in the floor and there will be a 200mm cavity with pumped insulation beads.
Any new under floor jobs we have done in the last few years the clients have specified for a air to water heat pump,so I would have gotten the complete system design spec and back up from a manufacture.

This client is insisting on fitting an oil boiler. We have done this in the past but some customers have complained of high running cost of running ufh with oil so we stopped. I would like to get this job right because it could lead to a lot more work for us. I hoping to get advice for keeping the system as efficient as possible i.e pipe sizing, boiler seizing anything else to keep the oil bill down...I have got advice from different suppliers but nothing really reliable.
 
Why not get a underfloor supplier to design it for you.? It's free!
 
How many loops on each manifold? That area, your looking at a minimum of 25 loops. depending on how many rooms and size. Quick calculation on my app is arund 17kw for heating load. Hot water and towel rails will be on top of that .

image.jpg
 
I took it to 3 suppliers and they designed a pipe layout which similar to eachother but when I mentioned an oil boiler was to be installed I got 3 Different suggestions as what way to pipe the system. Around here pretty much all new underfloor heating installs are being run by heat pumps and suppliers provide a good design service for that but when it comes to run it of oil/gas the advise varies a lot.
 
The 1st manifold has 7 loops with 470m pipe used
2nd manifold has 6 loops 405m
3rd manifold has 4 loop 255m
A pair of 32mm multilayer pipe was taken to the 1st 2nd manifolds
and a pair of 26mm multilayer was taken to the 3rd
The pipe centres are 150mm
 
Looks ok.
Have you got pumps and thermostiic mixing on each manifold?
Do you have stats in each room?
 
Yes pumps and mixing valve for each manifold. Suppliers opinion differ on using room stats some reckon it's better to have just one stat per floor to prevent constant boiler cycling and some are also recommending to use a system link which I have used in the past. Not sure they are fitted in the Uk much?
 
One room stat is common with ground and air source. But with oil, or gas. A room stat in each room is much better for control, overheating amd running costs. These need to be linked to the boiler.
 
Should of gone for liquid screed far more efficient for this kind of set up
 
Cheers for the advice on seizing the required load chalked. We probably over seized some boilers in the past and along with poor insulation, running cost would have been higher.
 
would have thought the only difference between an oil boiler install and a heat pump would be the pipe centers 200mm for oil and 150mm for the heat pump with pug screed on the first floor for the heat pump. can't see why a properly designed underfloor system would be expensive too run with oil
 
It's only expensive to run with oil when house isn't insulated properly and when used incorrectly with a sand cement screed for reaction times
 
There'll be underfloor fitted in the 1st floor also Gary. The Engineer specified 100mm screed for the ground floor base. There's pre - cast concrete slabs going in for the 1st floor with I'm gussing a 2" screed. I think the reason suppliers specified system links on underfloor systems was to a way to ensure the return temp back to the boiler was now so low it would cause condensation build up in the boiler chamber.
 
Why would it be so low as you put it
A 2inch sand cement screed will crack like mad better make sure they put a lot of fibre in it

Liquid screed and more insulation is your best betv
 
They reckon that if the water leaving the TMV to the manifold is 40c by the time it make its way through the loop and back to the the boiler it could be 30c which could potenally cause a build up of condensation in the boiler chamber.
 
And wouldn't it do the same with rads till it heated up

If it was that bad all boilers would need back end protection
Esbe valves or the like
 
A rad circuit would return a decent temp after 15 -20 min. Where's a ufh circuit would be retuning low temps to the boiler for long periods of time. Suppliers advised to fit a system link or else a homemade low loss header off the boiler to avoid this. The majority of ufh systems heated with an oil boiler that I stumble upon have system links fitted with them.
 
Lol I've fitted a hell of a lot and never seen either
And how do you size your home made LLH lol
 
Gray0689 said:
Why would it be so low as you put it
A 2inch sand cement screed will crack like mad better make sure they put a lot of fibre in it

Liquid screed and more insulation is your best betv
Click to expand...


Doesn't matter if the screed cracks we use a 28mm pug screed cracking doesn't affect the thermal performance of the screed
 
we're talking 1st floor pug screed you wouldn't use 100mm upstairs, and yes it's great for tiling on :icon4:
 
200mm rockwool chipboard flooring then pipes clipped to flooring between battens, pugscreed then ply on top pug screed.jpg
 
Yes as I have never done a joist house with underfloor upstairs
Always hollow core slabs
 
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