White Dog
Senior Member
This thread is a carryover from Ramblinman's discussion on furnace size from my FWC Options thread.
So here is what I've observed about furnaces in the various RVs I've owned or borrowed over the years. First, a bit of background which is probably well known to most but it's a starting point.
Furnaces produce heat to keep us warm (obviously) and are controlled by thermostats that turn the furnaces on or off. Contrary to my wife's belief, they are simply a switch that turns the furnace on and off at a predetermined temperature (sorry dear but turning the temperature setting on the thermostat to 90 will not heat the trailer up faster). Thermostats have a 'cut in' setting and a 'cut out' temperature, usually a few degrees apart. The 'cut in' temperature is the temperature at which the furnace receives the command to start and the 'cut out' temperature is the temperature at which the furnace is told to begin its shutdown cycle. 'Cut out' temperature is necessarily higher than 'cut in' otherwise the system wouldn't work.
Have patience, this is leading somewhere.
The thermostat tells the furnace to start when the temperature falls below the set 'cut in'
temperature. The furnace comes on and begins to warm up the camper. It continues to produce heat until the thermostat is warm enough to exceed the 'cut out' temperature then the furnace shuts itself down. However, the thermostat is often located in an out-of-the-way place and and has its own mass to warm up so it takes a bit longer to warm up than the air inside the camper meaning that the felt apparent temperature overshoots making it feel a bit warmer than the set temperature. Once the furnace shuts down, the camper will begin to lose heat until the 'cut in' temperature is reached, then the whole cycle will start over.
The point is, an overly large furnace will cause this overshoot to be excessive because it is heating up the camper too quickly. The thermostat lag allows the oversized furnace to run too long. I used to borrow my Dad's Starcraft camper that bragged about a large furnace. The problem was it was too large. We always felt too hot at the end of a cycle and to cold at the end - not really comfortable.
On the other end of the spectrum is a furnace that is too small for the size of the camper and the outside temperature. In this case, the furnace may never be able to get the inside to the set temperate.
What is important is to determine is whether the manufacturer picked the right size of furnace for the camper based on size and expected outside temperatures not simply the bigger sized furnace. Since both FWC and ATC are respected manufacturers, I would expect they would.
So here are a couple of questions for experienced FWC and ATC users:
1) Has your furnace been adequate to keep your camper warm in cold conditions?
2) What is the coldest anyone has used their camper?
3) In really cold temperatures, how often and for how long does the furnace come on?
I think this would be useful information for us all. To Ramblinman, I would suggest that the size of the furnace should not necessarily be the overriding feature in your decision about manufacturer until you hear from folks that have use these units in cold conditions.
Jeez, that was quite a ramble wasn't it!
So here is what I've observed about furnaces in the various RVs I've owned or borrowed over the years. First, a bit of background which is probably well known to most but it's a starting point.
Furnaces produce heat to keep us warm (obviously) and are controlled by thermostats that turn the furnaces on or off. Contrary to my wife's belief, they are simply a switch that turns the furnace on and off at a predetermined temperature (sorry dear but turning the temperature setting on the thermostat to 90 will not heat the trailer up faster). Thermostats have a 'cut in' setting and a 'cut out' temperature, usually a few degrees apart. The 'cut in' temperature is the temperature at which the furnace receives the command to start and the 'cut out' temperature is the temperature at which the furnace is told to begin its shutdown cycle. 'Cut out' temperature is necessarily higher than 'cut in' otherwise the system wouldn't work.
Have patience, this is leading somewhere.
The thermostat tells the furnace to start when the temperature falls below the set 'cut in'
temperature. The furnace comes on and begins to warm up the camper. It continues to produce heat until the thermostat is warm enough to exceed the 'cut out' temperature then the furnace shuts itself down. However, the thermostat is often located in an out-of-the-way place and and has its own mass to warm up so it takes a bit longer to warm up than the air inside the camper meaning that the felt apparent temperature overshoots making it feel a bit warmer than the set temperature. Once the furnace shuts down, the camper will begin to lose heat until the 'cut in' temperature is reached, then the whole cycle will start over.
The point is, an overly large furnace will cause this overshoot to be excessive because it is heating up the camper too quickly. The thermostat lag allows the oversized furnace to run too long. I used to borrow my Dad's Starcraft camper that bragged about a large furnace. The problem was it was too large. We always felt too hot at the end of a cycle and to cold at the end - not really comfortable.
On the other end of the spectrum is a furnace that is too small for the size of the camper and the outside temperature. In this case, the furnace may never be able to get the inside to the set temperate.
What is important is to determine is whether the manufacturer picked the right size of furnace for the camper based on size and expected outside temperatures not simply the bigger sized furnace. Since both FWC and ATC are respected manufacturers, I would expect they would.
So here are a couple of questions for experienced FWC and ATC users:
1) Has your furnace been adequate to keep your camper warm in cold conditions?
2) What is the coldest anyone has used their camper?
3) In really cold temperatures, how often and for how long does the furnace come on?
I think this would be useful information for us all. To Ramblinman, I would suggest that the size of the furnace should not necessarily be the overriding feature in your decision about manufacturer until you hear from folks that have use these units in cold conditions.
Jeez, that was quite a ramble wasn't it!
Plus, If I'd thought about it more before I bought my camper, I'd probably have a Wave 3 instead of the factory furnace.
