On Sunday, 26 November 2017 22:01:04 UTC, David WE Roberts (Google) wrote:
Following on from a couple of recent threads, and using
https://www.confusedaboutenergy.co.u...ic-fuels/fuel-
prices
as a reference.

John Runn said "If you fitted heatpump aircon instead, then it would be a
third to a quarter of the price for normal resistive heating."

That would give an electricity cost of about (15.4/3) 5.1 pence per kWh.
Possibly down to under 4p per kWh if the better estimate was met.

This compares to 7.1 pence per kWh for wood bought by the ton.
Smokeless fuel is 6.3 pence per kWh when bought by the ton.

This makes using a wood burner in the shed a pure vanity project.

Propane bottle and radiant heater comes in at 15.6 pence per kWh so that
is more expensive than normal electricity.

So on pure cost effectiveness on fuel use the air source heat pump seems
to win hands down.

It feels wrong to just have aircon in the shed because it is cheap to run;
I don't think I have ever been too hot because the insulated roof keeps
most of the sun away, the shed is shaded, and probably only needs heating
for less than half the year.

The kits linked to by Dennis seem to cost about £600. I would be saving,
say 10 pence per kWh (easier calculation) for electricity against normal
fan/radiant heating. So to get my money back I would have to heat the shed
for approximately (600 * 10) 6,000 kWhours.

{note - screw up in first run of the calculations. Forgot to use wattage
of heater.}

Which I think is not far off 10 hours a day for 2 years at 1 kWh or 5
hours per day of a 2kW fan heater.

Note that in the previous thread the calculation came out at needing 5kW
of heat to keep the shed at 21C when it was freezing outside. However that
was an extreme target as most times it wouldn't be at 21C nor would it be
freezing outside.

If this is correct then I need to work out how many 5 hour days I am
likely to spend in there.

If I were to spend 3 days a week over 6 months of the year, and only need
heating for 3 months of the year, then I would need heating for (365/4) *
(3/7) days per year. I work that out at 39 days a year.

Getting too late at night now, but if I am correct so far in my tortuous
working pay back would be (2 years) * (365/39) = 18.7 years.

So it looks as though an air source heat pump doesn't cost in for the shed
unless I am relegated to their for the rest of my active life and then
some. Or unless my calculations are well adrift.

Since it is already established that the stove is more expensive to run
than the heat pump and the installation of the chimney may be more
expensive than installing a heat pump then the wood burning stove would be
purely a vanity project.

Shame in some ways as having an air conditioned shed would be a definite
one up over the neighbours :-)

It does make the installation of air conditioning in the house look quite
attractive, though. Purely for cooling in the summer, though,


Solid fuel stoves are notoriously inefficient. Traditional ones may be only 10% efficient. Plus all the labour needed.
They are only worthwhile if you can get free wood.