On Thu, 05 Feb 2009 16:31:33 +0000, John Rumm wrote:
We've got quite a lot at our place here, running from cheap-rate
electric (which works out at about 3p/KWh - propane in comparison is about
double that for the same heat output)

What times of the day can you get cheap rate?

It's rather random - we're running on a load-control program here, so the
heaters shut down at peak times (with the propane furnace then taking
over) and in return get the cheaper rate. I think they reckon on about 2/3
of the time on, 1/3 off. Looking at the logs, the heaters ran yesterday
from 1am to 6am, then again from 8am right through to 7am this morning -
it's now 11am and they're still off.

Talking to an engineer the other day, the off-peak meter just slaves off
the main one, and they send a 220Hz signal down the line to tickle the
load control system into doing its stuff (small controller and a big box
'o relays in the basement - we've got the water heater and clothes dryer
on a separate circuit to the heaters)

I'm not sure if such a setup exists in the UK - I've only ever known
Economy 7 systems there, which seem to have more predictable cheap-rate
periods and don't outright switch stuff off at peak times! (but I'm not
sure their rate was quite as good - been a while, though)

It all works reasonably well, except that our propane furnace (and
associated forced-air ductwork) isn't the best, so it doesn't heat the
house nearly as well as the electric heaters can. I think we'll throw a
wood-burning furnace in this year too though, and that'll really sort
things out.

(plenty of space for a GSHP here too, but that doesn't seem to have quite
entered the DIY arena yet, and I have issues with paying someone else a
fortune to come and dig up my back garden when I could do that bit myself :-)

cheers

Jules