I didn't really want to buy the furnace that All Terrain offered. It uses 5 amps when it is running, so I thought it would be hard on the battery if I ran an electric fridge. Real Life: The furnace is not that big a problem in terms of the battery, depending on how much you run the furnace. The real problem is that running a high btu output furnace in a small space gives a wide variation in temperature. For all this, over 3 years, generally doing mild warming all night, I have used 7 gallons of propane.
I swapped the included thermostat for a digital Honeywell, the cheap two wire kind available at Walmart. This allows a 40 degree overnight temperature, and the heater does OK for this. When you set it at 70 degrees, when it is maybe 45 outside, you will get a big swing even with a short cycle. In the small Bobcat, the propane ignites at around 69 degrees and there is combustion for maybe 4 minutes. The furnace then clears the heat from the chamber, so the fan runs even though there is no burning of fuel. At the end of the cycle, the inside temperature is around 75. In fact, the temperature is layered. At the ceiling level it is around 80, but it is 70 at the floor. The swing of temps is called hysteresis. My home system kicks in and out with one degree of variation. The camper has about 7 degrees.
So if you are sitting there in the winter, when the furnace is helpful for a lot of evening hours, the standard combination will give you a lot of warm and cold periods, and a lot will depend on where you sit. Don't get me wrong. If you wake up in the morning and it is 40 degrees inside the little camper, the furnace will warm things up in a very short period, like ten minutes. It does a great job of maintaining 45 degrees at night, and preventing excess humidity. A very high humidity level is not good, at all.
Still, if you are winter camping, you might want to go the catalytic heater route. I've tried two units. The first was a cheap close-out from Walmart, a 20 dollar low output Coleman that was rated under 2000 btu. For reference, the furnace is about 18,000 btu. So, this is not going to do much when the unit is cold. It warms for a lot of hours, more than ten. You can use it and then boost the temp with the furnace every hour or so. It helps, but it's not quite enough. The Coleman sort of worked to maintain a decent inside temp until the outside temp was around 50 degrees. Both the cat heaters I have, the Coleman and a Buddy Portable, use the standard little canisters.
The Buddy heater goes the other way from the Coleman. At 4000/9000, it is keeping things at around 80 degrees on the low setting. Forget the high setting for maintaining a temp around 72. But wait, there is a nice way around this. If you have a ceiling vent, at least one with a variable speed, you can get enough cold air moving through to mix the air nicely, push in new oxygen, and maintain one temp. It's very easy. You need ventilation with a catalytic heater.
Coleman makes a 3000 btu heater. This is a good amount of heat, since 2000 was not enough, and 4000 btus was too much with no ventilation. I like using the power vent. It is safer, with this kind of heater. A single tank lasts 6 hours, which is maybe two nights. Walmart sells their brand of propane for $2.50 a canister.
You can buy the big tank hose for the Portable Buddy. It will go from a POL to a standard canister connection, without the canister. Now you are paying $3.00 a gallon for propane, not $10. I can actually route this hose from my propane tank, under the camper to the bed, and down through the slide opening for access to the camper tie down hardware.
Running the catalytic heater means the only electricity is the ceiling fan. For sleeping hours, the furnace can run with a low setting, and it won't cycle on very much down to about freezing, at least in the Bobcat. Then, in the morning, jump the thermostat and warm things up in a hurry with the big furnace.
It might be possible to design a thermostat with a narrower temperature range. I think if the heater ran for two minutes in the combustion mode (rather than 4 minutes), but cycled on more often, the temperature would be steadier. The Honeywell thermostat I have is trying to make a 1 degree swing, but clearing the combustion chamber of heat is driving the temperature up 5 degrees in the small space. A lot probably depends on the location of the thermostat. Running my ceiling fan with the vent closed, on a very low setting, helps to mix the air.
With the bigger catalytic heater the temperature will remain steady, there is no fan noise, and little pull on the battery beyond what the ceiling fan uses. Since the days are short for winter camping, it is nice to be able to use the evening hours and be completely comfortable 'inside'.
I like the Bobcat a lot, but I would have given up way before 3 years if it weren't for several small mods along the way to tweak the thing.
I swapped the included thermostat for a digital Honeywell, the cheap two wire kind available at Walmart. This allows a 40 degree overnight temperature, and the heater does OK for this. When you set it at 70 degrees, when it is maybe 45 outside, you will get a big swing even with a short cycle. In the small Bobcat, the propane ignites at around 69 degrees and there is combustion for maybe 4 minutes. The furnace then clears the heat from the chamber, so the fan runs even though there is no burning of fuel. At the end of the cycle, the inside temperature is around 75. In fact, the temperature is layered. At the ceiling level it is around 80, but it is 70 at the floor. The swing of temps is called hysteresis. My home system kicks in and out with one degree of variation. The camper has about 7 degrees.
So if you are sitting there in the winter, when the furnace is helpful for a lot of evening hours, the standard combination will give you a lot of warm and cold periods, and a lot will depend on where you sit. Don't get me wrong. If you wake up in the morning and it is 40 degrees inside the little camper, the furnace will warm things up in a very short period, like ten minutes. It does a great job of maintaining 45 degrees at night, and preventing excess humidity. A very high humidity level is not good, at all.
Still, if you are winter camping, you might want to go the catalytic heater route. I've tried two units. The first was a cheap close-out from Walmart, a 20 dollar low output Coleman that was rated under 2000 btu. For reference, the furnace is about 18,000 btu. So, this is not going to do much when the unit is cold. It warms for a lot of hours, more than ten. You can use it and then boost the temp with the furnace every hour or so. It helps, but it's not quite enough. The Coleman sort of worked to maintain a decent inside temp until the outside temp was around 50 degrees. Both the cat heaters I have, the Coleman and a Buddy Portable, use the standard little canisters.
The Buddy heater goes the other way from the Coleman. At 4000/9000, it is keeping things at around 80 degrees on the low setting. Forget the high setting for maintaining a temp around 72. But wait, there is a nice way around this. If you have a ceiling vent, at least one with a variable speed, you can get enough cold air moving through to mix the air nicely, push in new oxygen, and maintain one temp. It's very easy. You need ventilation with a catalytic heater.
Coleman makes a 3000 btu heater. This is a good amount of heat, since 2000 was not enough, and 4000 btus was too much with no ventilation. I like using the power vent. It is safer, with this kind of heater. A single tank lasts 6 hours, which is maybe two nights. Walmart sells their brand of propane for $2.50 a canister.
You can buy the big tank hose for the Portable Buddy. It will go from a POL to a standard canister connection, without the canister. Now you are paying $3.00 a gallon for propane, not $10. I can actually route this hose from my propane tank, under the camper to the bed, and down through the slide opening for access to the camper tie down hardware.
Running the catalytic heater means the only electricity is the ceiling fan. For sleeping hours, the furnace can run with a low setting, and it won't cycle on very much down to about freezing, at least in the Bobcat. Then, in the morning, jump the thermostat and warm things up in a hurry with the big furnace.
It might be possible to design a thermostat with a narrower temperature range. I think if the heater ran for two minutes in the combustion mode (rather than 4 minutes), but cycled on more often, the temperature would be steadier. The Honeywell thermostat I have is trying to make a 1 degree swing, but clearing the combustion chamber of heat is driving the temperature up 5 degrees in the small space. A lot probably depends on the location of the thermostat. Running my ceiling fan with the vent closed, on a very low setting, helps to mix the air.
With the bigger catalytic heater the temperature will remain steady, there is no fan noise, and little pull on the battery beyond what the ceiling fan uses. Since the days are short for winter camping, it is nice to be able to use the evening hours and be completely comfortable 'inside'.
I like the Bobcat a lot, but I would have given up way before 3 years if it weren't for several small mods along the way to tweak the thing.
