On 8 Nov 2005 08:28:46 -0800, Matt Beard wrote:

Alan wrote:
Next, you can do much better than 80% efficiency - try 95% and that
means an oil cost of £1323.

I'm assuming "real-world" figures - the 95% sedbuk figure is only
achieved when running at certain flow rates with certain temperature
differential (I don't know how fast it falls away though) and after 5
or 10 years I doubt that it will still run at 95% at any point.


Also, I'm not sure how large or energy efficient your house is, but 40K
kWh per year seems steep. I am only using 26K. I would get an accurate
figure rather than a rough stab as this greatly affects the payback
time.

The house is a detached granite building with not much insulation (and
little scope for improving it short of totally stripping out and
rebuilding) and it is in the north of Scotland. It takes a lot of
heating! Last year I spent just short of £2000 on electric heating and
it still felt cold.

I'm not sure if you are building a new place or adding this to an old
place but another factor to consider is that using under floor heating
is more efficient for heat pumps because they don't have to heat the
water up to very high temperatures. I've never been able to find out
accurate figures for the differences in efficiency though...

I hate solid floors - if I can't have a carpet under-foot I'm not
comfortable! I have rented houses with laminate and have relatives
with solid wood and even stone floors - I just can't wait to get back
home! So underfloor is not that good an idea (especially with suspended
wooden floors) so it's likely to be radiators.

Mmm.

Couple of thoughts

(i) Electriciy generation apart from nuclear (25%) and non fossil (about
5%) is mainly tied to raw fossil fuel prices. We do use coal a bit but the
bulk of electricity generation is gas., Gas is going up JUST as fast as
oil..so you may excpect electricity to actally go up anyway.

(ii) Burning oil at 60% efficiency to make electrcity that is transported
at 95% efficiency is not as efficient as burning oil in the home at 70%
efficiency.

(iii) insulation is what you need. Dry line that granite pile mate!

(iv) U/F heating will work with carpets. ...BUT what is critical is the
thermal resistance between the heat source and the room and the heat source
and the cold ground underneath., With a ventilated raised wooden floor
though, you are in trouble: You need massive underfloor insulation to
ensure the bulk of the heat transfer is upwards, and a higher in-floor
temperature to heat the room through the carpet. This may exceed sensible
limits with a wooden floor and lead to high levels of wood movement.