DIY Doctor

why is Underfloor heating so complex

Postby peterawilson » Thu Feb 26, 2009 8:37 pm

Forgive my naievity but can any one answer this conundrum.
Under my traditional wooden floor joists and wooden floor boards I have my central heating pipes running round the house. All nice and new installed by me and plummer in 2003. These pipes are stragetically placed around the house to give warm patches through the floor boards. In bathroom close to wash hand basin to give "warm" floor when heating is on. Why then can I not add in another say 5 metres of hot water piping under the floor boards as a under floor heating system all part of the existing heating circuit? Why do I have to use special pipes, a screed layer and a separate manifold etc...Which of course is excess cost excess hassle and appears to be about embedding the pipes in a floor that will be walked on.
Thanks in advance for the help
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Simply Build It

Postby plumbbob » Thu Feb 26, 2009 11:32 pm

Simply because under floor heating is designed to do something quite different to what you have got.

What must not be forgotten is, proper underfloor heating is designed to heat the whole room and not just the floor. The screed and substrate need to be able to transmit the kw's from the hot water over the whole floor area into the air of the room to make it comfortable. This can only be successfully achieved by there being a physical contact between the pipe and floor. Bunging a coil of pipe under a floor may result in warm feet, but little else.

Once the pipe is buried a whole range of considerations have to be taken it to account associated with the lifespan of the system and pipework. This type of heating takes a long time to warm up and a good while to cool down so accurate control is essential.
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Postby htg engineer » Fri Feb 27, 2009 7:06 am

I find it hard to believe the plumber gave any thought to strategically placing the pipes - they will run from the boiler to the radiators, if that happens to be underfoot at the wash basin - then it's probably coincidence.

Laying pipes in the way you're suggestsing will just increase the heat loss from the pipework the majority of it will be lost under the floor.

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