I'm trying to work out how much it would cost to heat my garage when
it's in more of a room like state, so there'll be good roof insulation
(already plasterboarded, just needs insulating), the walls are probably
going to be insulated plasterboard and the door will have some form of
insulation on it.

Using various online calcs and some finger in the air stuff I've come up
with some rough and ready values - are they realistic?

Sizes:

Roof - 36m2 with good insulation, u value estimated at .4
Walls - 72m2 with ok insulation (and crap on the door wall), u value .7
Floor - 36m2 no insulation, u value .7

Assuming a starting point of 0 degrees c, I'd like to work out how much
it would cost for frost protection (keep a steady 5 degrees) and also to
bump it up a bit further if I decide to put some of my more fragile
electronic stuff in there - so about 10 degrees.

So I figure I need to work out the heat loss, this seems to be total
size of area multiplied by the u value.

Roof - 36 x .4 28.8
Wall - 72 x .7 50.4
Floor - 36 x .7 25.2

Total - 104.4

To work out the watts needed, multiply the temp uplift by the heat loss,
so:

104.4 x 5 522w Frost Protection
104.4 x 10 1044w Ideal


So that gives me the size of heater I need - I was counting on something
like a 2Kw convector which we have in our conservatory and it really
does a great job, so this should easily be enough to heat the garage to
these levels, even allowing for underestimating the heat loss through
the door.

Assuming all that looks ok, and even if I'm quite a way off I've still
got another Kw+ before I need another heater, how do I calculate the
cost of the heater? I can easily do it per hour, but that assumes it's
on full blast all the time which it won't be - so how do you calculate
the cost based on partial use - is it even possible?


--
Mike Buckley
RD350LC2
XJ900S