"Jon" wrote in message
...
On 4 Mar, 17:30, "Autolycus" wrote:
"Jon" wrote in message

...

We've got a bedroom above the garage in our eight year old house
which
is always 5 deg C colder (or more) than the rest of the house on
cold
days. The fact that the bedroom floor is always cold leads me to
believe the insulation requires significant improvement between the
garage ceiling and bedroom floor.


snip

Could you put a suitably controlled larger radiator
in, or substitute a double for a single?

It's already a double.

With fins?

Larger rad = more load on boiler which is only
just the right size for a 4 bed house (cheap ass persimmon).

Is the boiler really running flat out, firing continuously, even on a
very cold day? I'd be surprised if the builder had calculated it that
closely. Older boilers can often have their maximum gas rate tweaked
(within defined limits, of course). Is it at its maximum rate?


Depending on how long you intend to live there, and how much of the
day
you need the room to be warm, it may even be more cost-effective than
buying lots of insulation. A quick look at the calculations for the
system I've just put in suggests that the most heat loss you could
hope
to save would be perhaps a couple of hundred watts.

You're not wrong. And I intend staying here for quite a while yet.

The floor will always be cold in the room as long as the lack of
insulation between the garage and the room above allows it. No matter
how much heat I throw in, the garage below will act as a heat sink.

It's true that insulating the floor will raise the temperature of its
upper surface, but I'm suggesting it may not be enough to raise the room
temperature much. The world acts as a heat sink for your roof and
walls, too, but you design accordingly. The energy transferred through
the floor is a largely function of its area, its thermal resistance, and
the temperature difference between the room and the garage. The thermal
resistance is the sum of the resistance of the elements of the floor,
including the surface effect. Unless the garage has a howling gale
through it, your bedroom floor is therefore no different to the
suspended timber ground floors found in many houses.

So do the sums: you'll find a range of values suggested for the thermal
conductivity of suspended floors, but take a sensible stab at it, and
play with the effect of different values of added insulation. Then
compare the cost with that of providing extra heat input, even if you
have to use supplementary heating occasionally.

Maybe I'd be better off insulating the garage. But the garage door has
so many gaping holes letting cold air in through the gap between the
frame that it'd not be cost effective either unless I changed the door
(expensive).

Insulate it iff you want a warmer garage for other reasons. Even if
insulating it pushed its temperature up 5 degrees, it will only make
perhaps 100W difference to the heat loss from the room, so perhaps a
degree or two to the room temperature.


--
Kevin Poole
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