Re: [SilverStreak] combination AC heat units?

["waymark1@xxxxxxxx" <waymark1@xxxxxxxx>]

We have a 1979 Instamatic heat pump. It has no heat strips (resistance heaters) 
as the trailer of course has a (Coleman) LP furnace.
The heat pump shuts off when the outside temp. goes below 36 deg. F as it can ice 
up at below that temp.
Compared to the furnace the heat pump is noisy just like any roof mounted A/C (air 
conditioning - more correctly air cooling)) unit. It does, though, heat the trailer 
rapidly when the outside temp. is 36 or above.
The big advantage of the A/C/heater is that electricity is much cheaper than propane. 
It works, though, only if you have adequate shore power available.
If you have 30 amp. shore power available you can heat no more than 3,450 watts total 
and that only if you have no other AC (alternating current) loads on. At 3.412 Btus 
= 1 watt that's only 11,700 Btus.

Our heat pump is rated 12,000 Btus. This is possible because a heat pump does not 
convert electricity to heat (except what its compressor motor wastes); rather it moves 
heat from one place (outdoors) to another (indoors). Our heat pump's literature says 
it moves 2.5 x as much heat as it uses in energy to move the heat. So it's using 4,800 
Btus of electricity (1400 watts or ) or just over 12 amps at 115 V to move 12,000 Btus 
from the air outside our trailer to the inside.
If you have 50 amp. shore power available (30a. + 20a.) and the load is evenly divided 
between the two legs you could get 2/3 more heat without overloading the circuits.
At any rate, resistance heat (heat strips) are very inefficient users of electricity 
and are quite limited in their heating capacity on a RV supply circuit.
As a comparison, our furnace is rated 30,000 Btus output. The furnace I installed in our 
'52 Spartan (originally an oil heater, I think) was rated 40,000 Btus output. And it 
wasn't really enough in north Idaho in the winter. A new, thoroughly caulked, 
weatherstripped, insulated and sealed RV might do better. A large RV with 2 furnaces or a 
motorhome with a diesel (oil) fired furnace will have even more heat available.
IMHO electric resistance heat is useful only for a small amount of heating in mild weather 
or to knock off the chill in a poorly heated corner of the RV. A heat pump can do better 
for the same current draw at temperatures well above freezing, like 40-65 or so degrees.

Our Lennox home HVAC unit can pump heat clear down to zero because it automatically 
reverse-cycles at intervals (goes to A/C mode with the fans off) to get frost off the 
outside coil. However, it produces only about 5,000 Btus at zero F. rather than the 100,000 
Btus it pumps at 40 deg. F., (there just isn't much heat left in the outdoor air at zero) 
so the heat strips (actually nichrome wire coils) are also operating below about 35 deg. F.

CO poisoning occurs only if the combustion chamber is cracked. A good combustion chamber is 
open only to the outdoors through its intake and exhaust vents. Every space heated with a 
forced air fuel burning furnace must have a functioning CO detector mounted near an inside 
heating vent. No windows near the furnace exhaust may be open during furnace operation, and 
all joints must be sealed - caulked - taped (real metallic tape, not "duct" tape, which has 
been obsolete since the days of natural draft furnaces) - gasketed - to keep all drafts from 
outside the unit from entering the RV. The furnace exhaust should not be on the same side of 
the RV as the door(s).
All fuel burning appliances produce at least some CO. Never heat with your RV's cooktop or 
oven, which should be used only during waking hours when people are moving around, going in 
and out, etc., and the range hood exhaust fan should be running during cooking.
Ventless propane heaters must never be used in a small space like even a large RV. If 
suitable at all, they are suitable only for use in large spaces like normal houses. They are 
not supposed to be used when people are sleeping, or in sleeping spaces at all. Never depend 
on oxygen depletion or CO detection devices to turn the heater off when someone is sleeping.

Some motorhomes have hot water heat in pipes in the floor. This system, though it uses a fuel 
(usually diesel oil) burning heater when the MH engine is not running, does not expose the 
water heater's combustion chamber to the interior living spaces of the motorhome. The only way 
CO can get from the water heater to the RV interior is by blowing in through a window or door 
after the exhaust has blown outside, or by faulty sealing between the heater chamber and the 
RV interior. I would love to install such a system in my SS. :-)

Al G.