| Author |
Message |
Peter Broadribb (Madbrit) (67.136.126.7)
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Votes: 0 (Vote!) | | Posted on Saturday, May 29, 2004 - 3:51 pm: | |
Having searched the archives and found nothing related to the subject, has anyone a website or the formula to calculate what size furnace one needs for a particular sized motorhome or box.
I have a 42,000 btu Suburban, which I bought for my bus, but I have been told it is too large for my 24ft conversion box and may well cycle incorrectly and not work very well.
Comments suggestions, etc as per usual rules..... LOL.
Peter. |
TWO DOGS (63.185.73.212)
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Votes: 0 (Vote!) | | Posted on Saturday, May 29, 2004 - 4:43 pm: | |
it will work fine Peter |
James Maxwell (Jmaxwell) (66.81.48.169)
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Votes: 0 (Vote!) | | Posted on Saturday, May 29, 2004 - 4:45 pm: | |
Peter: I'm not so sure there is a heat load formula for RV applications, given that the construction is generally sub-standard; I once saw a chart put out by Suburban but was not impressed with the accuracy of the calculations. However, presuming your construction and insulating efforts are at least a little better than the average commercial RV, you probably are a little oversized but I don't see it as a problem and if anything it is a plus if you are inclined to use your conversion in colder climates.
The claimed BTU output of most RV furnaces is grossly exaggerated in my opinion, and they seem to exhaust more heat out the flue than they put into the occupied space. They claim around 75% efficiency (comparing input to rated output), but a few yrs. ago I tested 3 different units, 2 being Suburbans, and found them more on the order of 60%. I think that if you calibrate the heat anticipator of your thermostat, you will find that you can control any cycling with that (It is a small sliding, fixed potentiometer found on most better stats and instructions for doing it should be included with the stat).
Most larger conversions and munufactured units have 2 35k furnaces and I have seen 3 in units of 40' or more. Just remember to put the stat at 60-66" off the floor, out of the discharge airstream, and as centrally located as possible and I think you will find that your 42k will work fine and be appreciated if you end up some place really cold. |
Tom Caffrey (Pvcces) (65.74.65.65)
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Votes: 0 (Vote!) | | Posted on Saturday, May 29, 2004 - 9:28 pm: | |
Peter, there are two kinds of heat loads and the usual way of addressing heating requirements is just a kind of approximation between the two.
If you have an empty room, the loss through the walls, floor and ceiling is most of what you are dealing with. Such a room will heat pretty quickly and cool quickly when the heat is turned off.
If you double one side of a cube, that means there will be a sixfold increase in surface area.
If there is a lot of mass in a room, such as storage, furniture, walls and doors, the heating load will be mostly a matter of interia. This means that the main problem will be how quickly it all heats up.
If you double one side of a cube, that means that the volume will be cubed, or eight times the same kind of mass could be present in that space.
Even though the difference in the two calculations doesn't seem very important, it's actually the source of most heating complaints.
Because of weight and space limitations, you probably will find that one furnace will do a pretty good job.
If you check your furnace, you may find that it has a valve on the gas line which will let you turn it down some if you need to. Ours does.
Why don't you try setting your furnace up temporarily and see what you think? You will most likely be the best judge if it will suit you.
Fast Fred has been known to suggest using a portable electric heater of 1500 watts (about 5000 BTU) to see how much temperature rise you get in 24 hours compared to the outside temperature.
Be sure to take your temperature readings in the morning, before the sun gets a chance to throw the results off. And if you feed 240 volts at 30 amps or better into your rig on a welder cord, you will be able to use a 4,000 or 5,000 watt heater or four portables for a test.
Good luck.
Tom Caffrey PD4106-2576
Suncatcher |
TWO DOGS (63.185.73.98)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 29, 2004 - 9:51 pm: | |
it will work fine Peter |
Peter Broadribb (Madbrit) (67.136.91.101)
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Votes: 0 (Vote!) | | Posted on Sunday, May 30, 2004 - 6:59 am: | |
Thanks Guys.
Peter. |
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