Tube and forced air

[Dragster Racer]

Sometimes opportunities are great, and sometimes they side track me.
I have a 40X40X15 that I am beginning to insulate this week. I have plumbing that needs to not freeze. (Nothing like planning ahead huh?)
So I am planning on a 30' tube heater. A friend from the past called me and told me that the furnace that he was going to use in his shop is not going to be used since he wants a wood burner. It is an crawlspace furnace, so it has a low profile. It has been checked over and converted to propane, and he has $200 in it. I am building a loft, so I could stick it up there and duct in the loft floor to blow into the garage area. It is 100,000 btu.
I think the tube will be more efficient and better and it will be my primary heat source. Should I use this at first and as a backup? It would aid in recovery when we open a door, and I could uses a lesser btu tube too because of that.
Just looking for opinions.
This is an always heated area.

 

[Dragster Racer]

Just looking for opinions..

 

[oldgoat]

I'd take it and use it and maybe you'll like it well enough that the tube heater won't be needed. If you still want the tube heater then like you said you could use it for a backup and recovery.

 

[krooser]

I heat 1200 sq. ft. of my shop with a gas-fired tube heater. Great unit but at 80,000 btu it's way bigger than I need. I should have put in a 50,000 btu but went with everyone's recommendations.

One thing you will love is the nice, warm heat it gives and it makes everyting in the shop nice and toasty compared to a forced air system.

 

[Dragster Racer]

Man I am glad you said something. mine is 40X40X15, and they were telling me I needed 207,000 btu. I thought that couldn't possibly be right. I couldn't afford to heat the place with that! I thought about a single 125,000, but that may even be too large. I plan on using at least one ceiling fan to mix up the air a little. What size do you think?

 

[rcleaver]

Why not calculate what size you need. It depends on a variety of parameters. I used HVAC calc for my needs. I got a limited use license for about $50. It also calculates duct size

http://www.hvaccomputer.com/startpagea.asp

 

[Charles (in GA)]

Here is a way to calculate it (from Northern Tool Co.)......

Which heater model is right for you? Start by determining the following about your heater needs:
How large is the area being heated in cubic feet? Calculate area dimensions (Length x Width x Height) = Total Cubic Feet


What is the desired temperature increase to be gained by the heater? Calculate (Desired temperature(with Heater) - Area temperature(without heater)) = Desired Temperature Increase


Calculate the BTU's required to achieve desired temperature. Calculate ((Total Cubic Feet x .133) x Desired Temperature Increase) = BTU's Required



The above calculations are estimates to measure your heating needs. Building construction contributes to BTU requirements also.


Quick Heater Sizing Chart - Find your approximate heater size quickly:
First column = Total Cubic Feet to heat
Other columns are BTU's of heat needed for Temperature Rise of 20 Degrees, 30 Degrees, 40 Degrees, 50 Degrees

5,000 CU. FT 15,000 BTU 20,000 BTU 27,000 BTU 34,000 BTU
7,000 CU. FT. 19,000 BTU 28,000 BTU 38,000 BTU 47,000 BTU
10,000 CU. FT. 27,000 BTU 40,000 BTU 54,000 BTU 67,000 BTU
15,000 CU. FT. 40,000 BTU 60,000 BTU 80,000 BTU 100,000 BTU
20,000 CU. FT. 54,000 BTU 80,000 BTU 107,000 BTU 133,000 BTU
30,000 CU. FT. 80,000 BTU 120,000 BTU 160,000 BTU 200,000 BTU
50,000 CU. FT. 133,000 BTU 200,000 BTU 266,000 BTU 333,000 BTU

******************

Another method I found......

Room area(LxWxH)x .133x degree of temperature rise desire...For instance,a garage 20'x12'x8'=1920 cubic feet Temp rise(-10 outdoor to +68 indoor)78 degrees So,1920x.133x78=19,918.08 BTU.So a 20,000 BTH heater would do the job,but would be operating a maximum output,unless bldg is tight and well insulated.Note#This is ONLY a rough estimator gauged for general heating of an average outbuilding.A well insulated tight building would require less heat,and a loose building or one with several windows/doors may require additional BTUs.

Thus, 40x40x15 (flat ceiling) is 24,000 cu/ft times .133 (thats point 133, the decimal is easy to miss) equals 3192 times the degrees of temp rise you need (lets assume 40 degree rise) equals 127,680 BTU.

You need to figure it based on the desired temp rise desired, and your knowledge of how tight and well insulated the building is and how many doors, windows, etc you have to round it up or down.

Charles

 

[Dragster Racer]

Those estimates make more sense than the ones I was using before. That's what I would have guessed my needs were.