On Tue, 29 Jul 2003 19:00:47 +0100, "Mungo \"two sheds\" Toadfoot"
wrote:

Hi peeps,

The thermostat that controls our central heating boiler is in the,
fairly small, hallway. Is this the best place for it?

If our living room and kitchen doors are closed and someone opens the front
door won't the stat think the house is freezing and fire up the heating?

Yes.

If
the stat's trying to get the hallway up to, say, 28 degrees, wouldn't the
rads in other parts of the house be getting hotter than they needed to?

Yes and no. There are two main components to heat loss - the first
being what is lost through the surfaces (walls, floor, ceiling, etc.)
and the second is heating the air. When you calculate heat losses
for radiator sizing (or use a program to do it), the surface losses
are accounted for by area, temperature difference and U value. The
heat required to warm the air is calculated on the basis that you are
heating the volume of air of the space at a certain number of air
changes per hour (generally 1-2 depending on the room, more for
kitchens and bathrooms.) Once the fabric of the building is warm,
the heat loss through the surfaces varies with the temperature
difference. If the building were completely cold and you turn on the
heating, you would also be putting heat into the thermal mass of the
building (mainly the bricks). However, once the fabric is warm,
opening the door for a short time is only going to mean that the air
needs to be reheated which does not require as long a run as the
initial start from totally cold. This would mean that the radiators
in the other rooms will run for longer than needed and the rooms will
overheat if you just have standard valves.



Our last house had the stat in the living room, which sounds a much better
idea to me - if the main room is warm then the rest of the house is too,
surely?

Again yes and no. Provided that you have no extra heat in there
such as a fire, you would get a reasonable result. Once you add
heat from another source, the effect will be to cause the room to be
warm enough and the CH only adding part of the heat. Its thermostat
will be satisfied earlier and the rest of the house will be cooler
than you may want. You can even get this effect if you have a
smallish but well insulated room and you get a number of visitors.
Each will add about 100W so 500W, which could be 25% of the heat
requirement would be enough to throw the system off.

I don't think that there is a perfect place. Kitchens and bathrooms
are out, so apart from hallways and stairs there isn't a huge choice.

Currently I have mine on an upstairs landing which is quite effective,
but I do also have an outside temperature sensor and I can program the
relative impact of one sensor vs. the other.



Also, I'm thinking of putting TRVs on all the rads so that the bedroom rads
can be turned down in the daytime. I'm guessing that they can just be
swapped with the existing valves (after draining down of course)?

Yes they can. Remember not to put one where the thermostat is going
to go or you will have two control systems fighting each other and the
system will likely run quite cold.


If I did this would it mean that I could leave the stat where it was? It'd
be a right pig to move and I'd rather not!

You could do. One solution you might like to consider is to use an
RF thermostat. The receiver can either go where the existing
thermostat is, or close to the wiring centre or boiler (i.e. where you
can tap into the wiring. With this arrangement you can take the
thermostat where you like and control that. In this case, having a
TRV on every radiator is more appropriate and then you simply turn the
one in the room where the thermostat is to fully open.

In any case, it is worth fitting a decent electronic type thermostat
because they operate more accurately and without the overshoot of the
bimetallic strip type. That would also have the effect of reducing
overheating in the rest of the house if the thermostat suddenly gets a
cool blast of air.









Any problems with this, or advice?

Ta,

Si


..andy

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