Re: Underfloor heating...

["bensbarn2001" <ben_wilkinson@xxxxxxx>]

Mark,

Sorry for the delay in replying but thought I'd contribute my 
experiences to this debate....


> 1: Would you recommend it?
Yes, absolutely.  It does have some issues with response time, but I
find these manageable.  As the house response time is pretty much 
predictable, it lends itself very well to advanced forms of control.
Other thoughts on this:-
Underfloor heating primarily works via radiant heat.  As this is the
type of heat which the human body is most sensitive to, you should be 
able to run u/f heating systems at a degree or 2 lower than 
conventional systems.  Hence they should ultimately use less
power.  
Radiators are primarily convectors and the air currents which are set 
up are a bit counter productive in terms of heating.

The response time varies depending on what substrate is being 
heated.  Some have mentioned heating plates.  These are attached
to 
floor boards in the case of a non-solid floor (such as wooden joists) 
and therefore are mostly used upstairs.   They add to the cost
and 
complexity of installation, although I'm sure some mfrs have been 
working on that since I researched this.  Wood floors using these 
plates don't have the response time issues associated with heating a 
large concrete base.  Neither do they have the large thermal mass 
when the system is turned off.

There is a limit to the temperature of the floor which is a 
compromise between comfort and heat output.  I think the standard 
temperature is about 29deg C.  When U/f systems were around in the
70s they got a lot of bad press because they were too warm.

At 29deg, the heat output from stone (or similar high thermal 
conductivity) is 100Watts/sqm.  It's 70W/sqm for wood and somewhere
between for carpet on a concrete floor.
As you can't take the temperature too much above this, then this 
becomes the limiting feature for heat output, and so calculating heat 
losses is critical to ensure that heat in will more than compensate 
for heat out (generally done at -1 deg C).

Someone mentioned that putting the pipes closer together increases 
heat output.  That's not strictly true, as all it does is reach 
operating temperature more quickly (ie decreases response time), 
although more heat will be generated during any ramp to normal 
operating temperature.

For solid floors and a wet system, the normal installation is to 
insulate the floor (minimum 25mm of celotex or similar), then put 
some grid or something to attach the pipes at 250-300mm centres), 
then put a layer of cement screed over the top.  Minimum thickness
for this is about 65mm.  Then you have to add the floor
covering.  
Wooden floors need attaching.  YOu can do this with glue, although I
used screws (shorter than distance to pipes).  So it's quite a lot of
depth all told.

I think others have described the electrical systems.

For my system I've got about 100mm of screed over the pipes, which is 
a heck of a lot of concrete to heat, but once system has been used 
for a couple of days (eg at the moment, mine is on for about 2-3 
hours twice per day), the concrete never cools down.  It's very nice
when going walkabout in the middle of the night.  The house needs to
be reasonably insulated because of the inflexibility of heat output.
I haven't had the response time issues that Mark M (I think) talked 
about.  I have individual control of each room and for some reason
the control system works very well as we're pretty much always very 
close to the selected temperature.  It's always surprised me that 
that's the case.


> 2: Can it co-exist in a house that also has radiators in other 
rooms.
Yes.  The u/f manifolds (I have 2, with a total of 20 loops of pipe)
need special mixing valves to reduce the temperature (done by mixing 
in return flow water).  Each manifold has a very big pump because 
it's pumping water around a km or 2 of pipe.

U/F heating is particularly suited to condensing boilers as the 
return flow temp is so low which helps the condensor work efficiently.

> 
> We have a lot of work to do in the sitting room, including 
replacing the
> old, nasty carpet, with a wooden floor. Mary would like individual
> control of each room's temperature, and is happy to do this with 
xAP /
> Homevision... but would also like underfloor heating.
> 
> Comments, suggestions, recommended suppliers?

Mine is from Wirsbo.  Very well established, reputable and first-rate
support.  I've had the system going for 5+ years with no issues. 
Some suppliers change pipe regularly and I liked the 25 year pipe 
guarantee Wirsbo offered.  A lot of other suppliers have grown up 
around the self-build industry and I would be very careful to ensure 
they've got some pedigree before paying money.

That's it

Ben




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