Underfloor water heating. Is it worth it

[Lk1980]

Hello All,
I am in the middle of the extension and my builder is suggesting under floor water heating. We have block and beam floor put on. I am wondering if anyone can help me answer the following questions

1. Is it cost effective to put the underfloor water heating on?
2. How thick the screed should be?
3. Once the screed is on the floor, how long does it take to fully dry.
4. Also to get it completely cured once the screed is laid, is there any method we need to follow / allow before the heating is switched on?

Any help will be greatly appreciated?

Many thanks,
LK

 

[SpecialK]

UFH is nice to have - Its amazing having warm floors in the winter. Great if you have tiles or LVT floors.

Only issue I have is the heating up times are much longer than rads and how long it then heats the room for. Fine if you are home all day but not ideal if you want an hours heat in the morning then are out all day to return later.

It depends what screed you have. Liquid screed can be 50mm deep. Put in as much insulation underneath as you can.

Traditional screed is 70mm+

As for drying you would need to follow the manufacturers instructions. You will have to wait ages until its dry enough to lay a stick down LVT...

 

[Notch7]

Hello All,
I am in the middle of the extension and my builder is suggesting under floor water heating. We have block and beam floor put on. I am wondering if anyone can help me answer the following questions

1. Is it cost effective to put the underfloor water heating on?
2. How thick the screed should be?
3. Once the screed is on the floor, how long does it take to fully dry.
4. Also to get it completely cured once the screed is laid, is there any method we need to follow / allow before the heating is switched on?

Any help will be greatly appreciated?

Many thanks,
LK

underfloor heating is very worth it in a new extension as there will be plenty of insulation underneath.
wet underfloor heating works well with modern boilers

bear in mind you need space for the manifold and pump
and you need flow and return back to boiler (I think)



I recommend using a different screed such as mapei top cem -it has better heat transfer for underfloor heating and it sets fast -within a few days

70mm traditional screed you are looking at 100 days to fully dry


you probably want 50mm screed over the pipes so 65mm -70mm is ideal

 

[Mister Banks]

I wouldnt have underfloor heating. I recently stayed for a couple of weeks in a house with UFH downstairs and an air force heat pump, the house was never warm.

 

[muggles]

I wouldnt have underfloor heating. I recently stayed for a couple of weeks in a house with UFH downstairs and an air force heat pump, the house was never warm.

That's not an underfloor heating problem

 

[Mr Chibs]

I have it in my kitchen, and it's great, it's linked to a combi boiler.
I have a limestone floor and when it gets a bit colder, the room never feels cold, and the ceiling is tall and vaulted.

Personally I won't find another radiator now, unless I really have to.
Obviously, floor covering is a deciding factor.

 

[muggles]

1. Yes - UFH is cheaper to run than radiators
2. Screed should be to the manufacturer's specified depth. Ideally you should have a liquid screed with UFH as it gives better heat transfer, and you need less of it too - you can get away with as little as 45mm with some liquid screeds. You should also be aware of the insulation thickness below the UFH - minimum 100mm and ideally 140mm of Celotex or similar
3. Liquid screeds usually say 1mm depth per day but it does depend on atmospheric conditions
4. Heat it up slowly

 

[Mister Banks]

That's not an underfloor heating problem

Wow, instant diagnosis ! Joking aside, I dont know what the problem was, it just didn't warm the house.

 

[Madrab]

There are also alternatives to screed/thermal mass UFH now. Overlay systems are very effective, have very quick heat up times and are much easier to retrofit than pouring concrete but comes with the same cooler running higher efficiency operation. Installation outlay can be higher initially though.

 

[Lk1980]

Hi Madrab, sorry I am completely new to this. Are you able to give the example of overlay systems which I can discuss with my builder

 

[Madrab]

An overlay system comprises of a low profile (~20mm) high density insulation board that is routered to take either 12mm or 16mm UFH pipe, it is laid directly onto the existing flooring and then overlaid with the final floor covering. It comes with an aluminium coating that acts as a heat spreader. The final floor covering ( wood/tile) can then be laid directly on top due to the density of the board.

Recently installed a proof of concept idea using a 6mm cement backer board topper to allow it to take an underlay and carpet.

The controls are the same and it runs at the same low lemp and heats the space the same way but can be controlled like a normal central heating system rather than having a large thermal mass to keep warm.

 

[ericmark]

1. Yes - UFH is cheaper to run than radiators

1. If heating wanted 24/7 UFH can be cheaper to run as the water temperature is reduced, so heat pumps work better and boilers gaining latent heat work better, but this is only true if no radiators are used, if the boiler or heat pump needs to supply a radiator then no real gain, the main problem with UFH is speed, and the better insulated the home is the more speed is important.

The fan assisted radiator is likely the fastest transfer method, it has low water content so less heat is stored, and the fan distributes the air fast, this is why we use it in a car. However there is a problem, it needs a high flow rate and when fan is off hot water exits the unit, this can upset a boiler using latent heat recovery, likely would work better plumbed in series instead of parrellel, one odd one in kitchen works well, whole house noise is a problem.

So radiators need to have large surface area, but low water content to speed the transfer of heat, which is required if home not heated 24/7.

The idea is if you arrive home at 6 PM the less time before that point that heat is required the better.

Also the sun through windows, if sun can heat the room in 2 hours through the windows, then the central heating must cool down to zero output also in 2 hours. So the more windows which catch the sun, the faster the central heating needs to respond.

So UFH may work fine in an old persons home, but even retired I program my TRV's so rooms only heated when required.