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Author Topic: BTU to Square or Cubic Feet  (Read 6071 times)
TomC
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« Reply #15 on: November 29, 2007, 08:16:35 AM »

On my 40 x 102 transit with very large windows, but with 2.25" sprayed insulation, I have one 35,000btu propane furnace that keeps the bus warm down to 25 degrees (coldest I've been in).  It runs for about 5 minutes then off for about 30 minutes (70 degrees- less running time at 65).  If it got really cold, all three of my roof top airs have heat strips, and they do work if you close off the vents to slow down the air flow.
In above freezing weather, two heat cubes work well also.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #16 on: November 29, 2007, 01:44:14 PM »

Hay Capt. Ron,

I have a program the can exactly tell you how many btu's your bus will need to maintain a certain tempature.

It's is a load calculation that we use for customers to recieve rebates from equipment we install for them so we can

prove to the utility companys that we have installed our equipment to their standards. I usually charge $750.00 to the

customer for this service and they now only get about $500.00 back in rebates.  Angry  [No charge for you]

Just give me a call and we can walk through the questions. "there is alot" Tongue

Nick-
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Whatever it takes!-GITIT DONE! 
Commercial Refrigeration- Ice machines- Heating & Air/ Atlantic Custom Coach Inc.
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John Z
1959 GM PD-4104 4139 Northern Minnesota
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« Reply #17 on: November 29, 2007, 01:47:55 PM »

A related question,,, does anyone know how many BTU's are available from the cooling system on a stock 671 while OTR?
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Tim Strommen
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« Reply #18 on: November 29, 2007, 02:31:26 PM »

Hi guys,

    A while ago on the other board, I posted an HVAC calculation spreadsheet (picture below).  I can make this tool available again, if you email me (address in profile).

Cheers!

-Tim
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Fremont, CA
1984 Gillig Phantom 40/102
DD 6V92TA (MUI, 275HP) - Allison HT740
Conversion Progress: 10% (9-years invested, 30 to go Smiley)
pvcces
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« Reply #19 on: November 29, 2007, 06:20:09 PM »

John Z, if you figure out how many gallons per hour of fuel the 4104 is burning on the road and multiply that by 140 KBTU, you will have your BTU into the engine. Roughly 1/3 of the energy is making mechanical energy, another 1/3 is heat out the exhaust and the last third is absorbed by the cooling system.

This means that you can recover a good part of the cooling system part for heating the inside of the coach.

For example, if you run 60 mph and get 10 mpg, you are using about 6 gph, or about 840,000 BTU. One third of that goes to the cooling system, or about 280,000 BTU.

I expect that 1/2 to 3/4 of the cooling system heat ought to be available for heating in moderate weather, or somewhere around 200,000 BTU. You're going to have to go some to get that much heat out of any furnace.

As the outside temperature drops, the amount you can take from the engine will be reduced until you get to the point that the engine will not stay up to temperature. Then, the amount you can take from the engine will really fall.

We would not willingly give up our bus heat.

Tom Caffrey
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Tom Caffrey PD4106-2576
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« Reply #20 on: November 30, 2007, 05:17:33 AM »

My interior is about 90% done and no offense but that is a bad idea. Just think one screw or nail in the wrong place  Angry 

That would go, I would think, for any wall, floor, or ceiling with wires or pipes.  It's not necessarily a bad idea, but it may just be one that you don't wish to implement.


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John Z
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« Reply #21 on: November 30, 2007, 07:07:24 PM »

Thanks Tom. I just bought two bus heaters that are rated 80,000 BTU each at max. So i was wondering how well those would work plumbed inline behind the oem heater/defroster. From you info, it sounds like they should work out pretty well. I am going to save your answer into my '04 notebook.  John Z
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« Reply #22 on: November 30, 2007, 09:00:32 PM »

You're welcome, John Z.

If those are school bus type heaters, the main complaint that I remember of them was that they were usually noisy. If you haven't checked out the noise level yet, you might want to try them out before you install them.

For what it's worth.

Tom Caffrey
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Tom Caffrey PD4106-2576
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captain ron
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« Reply #23 on: December 02, 2007, 05:15:41 PM »

Well I installed 20 feet of base board heat in my living room/kitchen area and It's too warm in here right now. I have to use the bedroom thermostat to control all of my heat until tomorrow so I have to turn it up a little too high so the front Aquastat don't close before it gets warm up front (have them hooked together right now). My dog is not shivering so it must be good Grin
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jdr
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« Reply #24 on: December 02, 2007, 05:45:08 PM »

My MCI9 is foam insulated with 8 dual pane windows, 1" insulated windshield cover and no floor insulation. 15300 btu is good for 68-70 degrees with outside air temp of 15 degrees. I hope to improve on this a little with some more detailed insulation up front. Jim
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buswarrior
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« Reply #25 on: December 02, 2007, 06:10:45 PM »

Hello

Something else to think about...

It takes a lot more heat to warm up a cold coach, than it takes to keep it warm.

If you can design an efficient system for maintaining temp, with accessory ways of bringing big BTU online for those times you find yourself with a cold coach....

Best of both worlds!

Costs/cycling of running an oversized heating unit may be less than adding the big BTU accessories to a smaller system?

Webasto DBW300 (100 000 BTU) plumbed inline to the stock coach heat sure warms up the 8V71 and the coach in an "adequate" length of time in the northern climates!

FWIW, the Webasto has a fuel return to the tank, some minor warming from that?
Stirring around at the minimum.

happy coaching!
buswarrior
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Frozen North, Greater Toronto Area
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