How many BTUS of heat do I need in my bus?

[belfert]

What is a good way to come up with the right number of BTUs of heat for the interior of my bus?  I have a Proheat iesel heater that is 45,000 BTUs.

I'm mainly concerned right now about heating the front living/kitchen area that is just about 20 feet long from the windshield to the first wall.  The space is about 78" tall by about 98" wide.  I've heard that 15 BTU per cubic foot is the right number.  That puts me at about 15,000 BTUs for that space.  My understanding is that temperatures will fluctuate more if there is too much heat output by my fan heaters.  I am also wondering how many additional BTUs I need to deal with air infiltration running down the road?

My thinking right now is one 16,000 BTU fan heater and another 7,000 or 8,000 BTU fan heater.

[luvrbus]

The average drivers heat in the drivers area on a bus is 30,000 + btu 15,000 maybe cutting it a little thin in Minnesota

good luck

[belfert]

Right now if I used the two fan heaters I have been looking at I would be at 23,000 BTUs.  I might want to go even higher, but going higher means the fan heaters get larger and more expensive.

I don't plan to take any more trips in the Minnesota winters, but I should probably be prepared just in case.

[bevans6]

I think it depends on a lot more than you have said.  How cold will you you use it, the insulation factor, etc.  My MC-5C, if I were to use it below 30 degrees for long, I would need at least 45K BTU of furnace.  That would get me by in day time highs of 30 degrees and happy.  I don't think there is a problem with too much heat if you can control the output temp, which you usually can. 

Brian

[robertglines1]

not knowing your insulation or glass area.  I have 2 1/2 inch foam in roof and side walls  45 ft coach 3 slides  only 8 side windows plus windshield.  min in floor.  single didgets.  16,000btu cat heater cycled on and off.    Bob

[belfert]

I spent some time in the bus this evening looking at possible heater locations and thinking about sizing of the heaters.  My front area is nearly 20 feet long including driver's area.  The two windshields are each 4 feet wide by 5 feet tall.  I have four side double pane windows that are each 3 feet x 4 feet (big windows).  Most of the heat loss would be in this front area especially when driving.

I'm thinking about doing two 16,000 BTU fan heaters now each on opposite sides of the bus about 5 feet apart front to back.  Later I would add another 8,000 BTU fan heater for the driver.  Would 40,000 BTU of heaters in the front alone be too much for a Proheat that is only 45,000 BTU total?  The back bunk area will get probably a 16,000 BTU fan heater.

[luvrbus]

The 45,000 btu is just to heat the water you see those with radiant heat on each side of the bus tied into the factory drivers heat with 4 or 5 heat exchangers through out the coach and heated bays they don't have a problem, I guess you could have to many exchangers but I never saw it

good luck 

[gus]

It is impossible to guess the btu requirement for a bus because there are so many variables in each individual case. The original bus heat will drive us out in our coldest weather if I leave it on, but our coldest is mild compared that in the frozen wastelands of MN!!

If 45,000 btu is the max output you can't possibly get more than that from the front heaters, actually less because of heat line loss.

[belfert]

My bus heat is mostly gone because it was partially tied into the air conditioning.  The bottom part of the luggage racks actually was a duct for the air conditioning and part of the heat.  The rest of the heat came from baseboard radiators the length of the bus that I took out as they were in the way.

Dina was a Mexico designed and built bus that never had good heat because it doesn't get that cold in Mexico.  The driver's heat and defrost is still in, but it doesn't very warm below about 40 degrees.  MCI/Dina issued a number of engineering change orders to try to improve the heating in the field.  There was an 80,000 BTU Webasto plus engine heat, but getting the heat to the inside and front of the bus was the issue.

I ordered two 16,000 BTU fan heaters today.  They will be wired as one zone with one thermostat.  Down the road when I have more BTUs of fan heaters than the output of the Proheat I'll just have to live with reduced output if all zones want heat at once.

[robertglines1]

Brian: I know as you go every time you get a chance you add insulation and plug possible air leaks(cold). Keep up the good work. I have found out the biggest loss of heat is thru the front area both glass and skin. Very little insulation there from factory and constant air flow when moving causing heat transfer at a huge rate.  Prob takes twice as much going down the road to heat same area. I eliminate as much of the thin frontal skin as possible with overhead cabinets with insulation behind them and lower cabinets under dash with same.

[luvrbus]

Brian, you seem to have a reservation about the 45,000 btu handling your load so I thought I would post this for you, a friend had his Aqua Hot shipped here to install this winter this is his system same BTU has yours  

1 38,000 btu defroster and heater for drivers area
3  8,000 btu exchangers
2  4,000 btu exchangers for the bays
1  4,000 btu  exchangers for the a the bath room
engine pre heat
instant hot water
He lives in cold country also Alaska,I saw the bill on his man those Aqua Hot are pricey

[belfert]

I may be overdoing it on the heat for my front living area if Clifford only used 8000 BTU exchangers for areas other than the driver.  I am still using the bus heat for the defrost so I don't plan on anywhere close to 38,000 BTUs for the driver's area.

But, as Nick said you really can't have too much heat.

[artvonne]

  Not a Bus, but good for comparison. Our old (1992) Bounder is 32 feet long, and has a 25000 BTU output furnace. As long as were not moving, it stays very comfy down to about 10-20F (havnt been in any colder weather with it). The walls and cieling are 3 inch foam, but there is ZERO insulation in the floor. There was also zero insulation on the front nose. I mean none. And a thousand air leaks. Ive done my best to tighten up leaks and insulate, and its a lot better, but I just found a major air leak in the outside upper corners of both windshields.

  So like I said, parked and sitting we were always very comfy. But roll the curtains back and start pushing it into the wind and there have been times it was almost unbearable, where we ran the generator and plugged in electric heaters up front. It has a dash heater, but the morons ran all the heat ducts outside the firewall, so by the time it gets to the vents its like baby breath.

  As for how many BTU it "should" take, there are calculators that can be used, but you have to be careful as air infiltration on the highway can totally kill your calculations. So while oversizing a heating system in a home is inefficient, oversizing a system in a Bus could be more of a compromise. You wont likely ever need more than 20K btu sitting parked somewhere with the curtains pulled, especially if your real well insulated. But out on the super slab its a whole different picture. Remember, at 70 mph it like were driving into hurricane force wind, and if its cold, it could take a lot to heat it if it starts leaking in.

[luvrbus]

You can have a bus or a RV as tight as possible they still are like a vacuum cleaner going down the road only way to solve the problem is over size or over power the loss

good luck

[buswarrior]

And don't forget the rate at which you will be able to warm the coach up inside from cold.

Think of BTU like you do horsepower.

The rate of acceleration needs lots of HP. Cruising takes a lot less.

Think of it like those in the cold have to accelerate to a higher speed than those in the warm.

10-15K of BTU may keep a well insulated coach warm below freezing, but it will be a long, long journey from cold to warm with so few.

Another variable to fiddle with!

happy coaching!
buswarrior