Physically Impossible Heating Claim
For those of you that are debating this issue, I have done some fairly
simple calculations to determine the relative energy costs for heat based upon
some local pricing (we get charged a fortune for shore power at this marina):
For propane (assume essentially 100% efficiency for an unvented portable
unit such as 'Mr. Heater' or your cooking stove):
at $12.00/20# cylinder - 2.5 cents per 1000 btus
at $2.00/1# disposable bottle - 8.3 cents per 1000 btus
For resistance heat at 20 cents per KWH - 5.86 cents per 1000 btus
For resistance heat at 12 cents per KWH - 3.52 cents per 1000 btus
For heat pumps (using my units which average 1920 watts (including the
pumps) and putting out 16,000 btus nominal, probably 14,000 btus for real with 55
degree seawater):
at 20 cents per KWH - 2.75 cents per 1000 btus
at 12 cents per KWH - 1.65 cents per 1000 btus
These power KWH rates are shore power numbers; if you are having to run a
generator or big battery bank to make this power - energy (and set-aside
capital) costs rise dramatically.
I don't have data for diesel-fired vented heaters that are more common in
the PNW and NE. Anybody got it?
There is a reason heat pumps are popular (they pull 'free' btus from another
medium and 'concentrate' it to higher temperature. They don't create heat,
their energy consumption is used to 'move' it. They run the other way in the
summer). But they dramatically lose ability to pump heat from the working
fluid (seawater in our case) into your cabin air if that fluid is below 40-45
degrees F. Hence resistance heat strips in some units. And why diesel
heaters are so welcome.
(If you have the discipline to not forget, kluge the intake to a lower depth
to see if you can find warmer (or cooler in the summer) water. Not
advisable when underway! Also, might create problems if you lose 'prime')
For space heating, a BTU is a BTU. Cannot be created by Amish craftsmen and
soapstone or ceramics or oil filled radiators. For 'hot on the face, cold
in the room' radiant heat, it's still true, but that's slightly different due
to perception of comfort.
Evaluate capital costs and relative safety and condensation and freedom from
shore power and noise and space limitations and bragging rights and greenie
merits, but BTUs and resultant temperature follow the laws of physics. Most
boats leak air like a sieve and have no insulation, so don't expect much
better thermal retention than a camping tent. And also remember, the greater the
temperature differential between the inside and outside of your boat, the
greater the rate of BTU transfer.
My $.02. Jim
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For those of you that are debating this issue,>>>>>>>>>> snip <<<<<<<<,,
BTUs and resultant temperature follow the laws of physics.
Most boats leak air like a sieve and have no insulation, so don't
expect much better thermal retention than a camping tent. And also
remember, the
greater the temperature differential between the inside and outside of
your boat, the greater the rate of BTU transfer.
My $.02. Jim
REPLY
From my own days of living aboard during winter in Toronto, the boats that
had a "tent" or winter covering over them were always warmer than those
that did not. With -20 F and chilly winds it was a bit on the rugged side.
Most of the heat leaks are in the super structure, so a winter cover that
goes down to the gunnel creates an outer shell of relatively dead air. You
eliminate the wind chill factor.
We used canvas back then but today you can get white shrink wrap plastic,
or simply use 10 mil grade construction grade poly sheeting to create a
green house effect.
Agreed this is not convenient if you plan to take the boat out for
occasional winter cruises. In which case, you should be looking for a
floating boat house for winter wet storage.
Jim's cost analysis is fairly close.
One thing about diesel fired furnaces. You most likely got summer grade
diesel in the boat tanks. For best and cleanest ( non smoking non carbon
build up ) you should be burning winder grade #1 diesel.
We have had this discussion before. Some people went so far as to have a
small separate tank for their diesel furnace and filled it with the best
grade of fuel to prevent carbon build up problems with their burners.
the smaller Espar and Webasto models seem especially prone because in he
smallest burner sizes, the metering nozzle is incredibly tiny and more
likely to suffer if there is anything amiss with the fuel.
Arild
Jim,
That was a good set of cost numbers you posted. To summarize:
Resistive electric = 5.9 cents per 1,000 BTUs
Propane = 2.5 cents per 1,000 BTUs
Heat Pump = 2.8 cents per 1,000 BTUs
The additional price point to add to that is the cost of oil heat. At current rates of about
$2.00 per gallon, and given that a gallon of diesel contains 139,000 BTUs/gallon, if a furnace
is 85% efficient (the rest of the heat goes out the exhaust), that gives us an oil heat cost of
1.7 cent per 1,000 BTU!
Kevin