Radiant heat calculations?
I got some good answers in my thread about propane storage but I'm trying to figure out a bit more information on the typical usage for LP on board a bus. It's looking like I might get a coach right now and so there's plenty of under-bus storage for utilities like water tanks (especially since I won't have a black water tank), batteries, and propane tanks...but I need to budget space for a heating system which can be a bit more complicated.
I've tossed around the idea of using a few different systems and compiled some pros/cons of each...
Between wood heat, RV furnaces, electric heaters, and radiant heat I think that radiant is the best option. There are a few reasons, first of all it's quiet and works completely in the background, very little input is necessary from the inhabitant. The systems are generally regarded as being energy efficient, and the cost isn't too extreme from what I've found so far. On top of that it means that the floor will always be warm and I'll be able to walk around in the dead of winter in my bare feet. When we put an addition into our current home the master bathroom got radiant floor heat and it's so nice in the winter to not have to put socks/slippers on to go to the bathroom.
Anyway, for now I want to plan for radiant heating. If anybody has experience with this type of system in a conversion I'd love to hear it!
I have chosen to run a closed loop system, this means one hot water heater for the floor and one for domestic use. Because I'm doing a closed loop I can also use the radiant heat to heat the diesel engine in the winter which will be of great benefit on ski trips that take me into the mountains in the dead of winter.
Finding a properly sized water heater is proving to be difficult. First of all I am not really sure how to calculate the BTUs required for the space. I've googled "BTU calculator" and plugged the same information into a few calculators and gotten different numbers ranging from ~8,000 BTU all the way up to ~75,000 BTU and some in the middle.
So assuming the high end of that BTU rating is the accurate one, do I just look for a water heater with a 75,000 BTU output rating? Would that mean it's on all the time? Should I be looking for a 150,000 BTU rating heater? I'm not really familiar with all this heating stuff.
The plan is to use rigid foam underneath the floor that the radiant is in, and blown in insulation in the sides and ceiling of the bus. I also plan to insulate the accessory bays under the bus that house the water tanks so they don't freeze in the winter.
Then my other question is about gas consumption, how much should I be expecting to consume with a hot water heater tasked with heating via radiant heat?
Sorry for so many questions but heating is one place I'm a bit overwhelmed...the bus will surely be used on days where it gets to -15F or colder at night and barely above 0F some days. Last night it was below -20F here but that's probably the coldest night of the year so far.
Any help would be appreciated!