View Full Version : OT What copper to use for propane furnace?

Your Old Dog
10-16-2007, 07:31 AM
I'm giving up on my wood burning stove in the shop. I can't seem to get enough draft and at $89.00 for 3 foot section of chimney material to satisfy code I've bought enough. I ain't buying anymore.

I bought a used thru the wall vent type space heater that looks big enough to heat my shop. I bought 2 100 pound propane tanks.

The plan is to place the tanks around the corner of the barn so I can get to them in 3 feet of snow to take them to get refilled. This will leave me with about a 50 foot run of copper tubing to reach the furnace.

I found a chart that says for 30K furnace at 50 feet I need 3/8's tubing. It does not say "what" kind of tubing? Do I want K, L, M or whatever to make this work. The tubing will be run up from the tank, across the eves and down to the furnace. It will not be run in dirt.

Any help on this would be appreciated. I'm tired of waiting hours for the shop to warm up only to have the wind direction change, cause a back draft and fill the shop with smoke. Time to modernize !!

thanks for any help you can offer.

10-16-2007, 07:53 AM
I have a 30K Modine that I ran about 25 feet of 3/8" soft copper tubing to, and it works fine. You can get it in rolls, and probably 50 feet. If not, use flare a coupling. I'm not sure if soft tubing that small comes in "grades", like larger copper pipe does. Most regulators have fittings that are 3/8", but there would be nothing wrong with running half inch tubing to give extra volume for long runs.

BTW, since you are using two tanks, I got a "change-over" valve, that will switch to the second tank when the first runs out. Sure does save the day on cold days. I think it's made by Marshall. RV places sells them.

10-16-2007, 07:57 AM
I assume this is fairly low pressure.

Personally, I would call an expert, but I guess I'm more cowardly than you are. If I had to do it myself, I would probably use 3/8" flexible copper, not rigid, and run it inside flexible plastic conduit, but I really don't know the first thing about code requirements for this sort of job.

If you want to use rigid, I'd at least use L tubing, or K if I was feeling doubtful. Not M -- while it would probably work, it's pretty lightweight stuff.

10-16-2007, 08:25 AM
You can't be too careful around propane: http://www.king5.com/topstories/stories/NW_101507WAB_truck_driver_dies_LJ.171c438af.html

10-16-2007, 08:33 AM
K, L and M are water pipe designations. You want 3/8" soft copper tubing, not water pipe. Check your local code. You should mark the tubing with yellow every meter or so or just give it a spray across the roll with yellow paint before using it. This identifies it as containing heating gas.

10-16-2007, 12:53 PM
As RWS stated, I have seen many LP installations where what I know as "refrigeration tubing" was used. With the current price of copper, you may want to look into polyethylene gas line. See here:


10-16-2007, 06:21 PM
As RWS stated, I have seen many LP installations where what I know as "refrigeration tubing" was used. With the current price of copper, you may want to look into polyethylene gas line. See here:


Actually, refrigeration tubing is probably better than the regular soft tubing, since it has a higher pressure application, and it's "clean pipe". But it's overkill.

Propane operates on only a few pounds, and most any soft copper tubing will suffice. Don't bury it under a structure(underground is OK, but not in a crawl space), keep your tanks at least 3 feet away from a window, door or crawl space vent. Once you've connected the lines, open the tank valve and soap the joints, looking for bubbles. Propane has an additive that smells like something dead, for a reason. So you DO smell it.

Your Old Dog
10-16-2007, 08:49 PM
Thanks for the help guys. I may have found another way around the problem, at least while I'm in the testing stages.

I located a 12' long propane hose I had for running a grill off of a 20 lb tank. It will be long enough to test out my system by mounting the 100 lb tank outside the area where the furnace will be mounted inside. If the furnace works well enough on the shop then I'll get the soft tubing and spray it yellow as Evan suggested for safety reasons. It will sure be nice to be able to get away from burning wood stove. By my rough calculations I should get about 3 weeks heat of 8 hours per day at 20 degree temps from my 100 lb tank. This is based on 91,000 btu per gallon, my 100lb tank holding 23 gallons and a 30K btu furnace. Assuming it won't run continously but rather cycle on and off in a well insulated shop it's looking like $25.00 per week to heat the shop. That's just a little more then what the wood stove was costing me.

10-16-2007, 09:15 PM
Here's the answers from a gas fitter in BC, fwiw.

Evan is right about refridgeration tubing, this is what was code accepted up until recently. Now we are supposed to use "gas tubing", same spec. for wall thickness as refridg. tubing, just has a yellow coating on it. It is available in most common tube sizes.

Either one would be OK to me. DO NOT use the cheap rolls of copper tube from Rona, Home Depot, etc. They are not approved for gas use and seem to kink way too easily. Looks like the wall thickness is thinner, but I didn't measure it.

Type K soft copper is/was approved for direct burial, but I'll second the suggestion to get a poly. line with risers made up if you need to go underground. Poly piping isn't approved for surface mounting or interior use.
That's mostly what the gas utilities use these days.

You can use type L or K piping (copper water pipe) inside or surface mounted, but all joints must be "sil-fos" brazed, soldering is not acceptable.
I mostly use flare fittings, and do most of my branch piping in 1/2 od tubing, as it is almost as easy to install as 14-2 Loomex.

If labour cost is a factor, there are also systems of flex. stainless piping (comes on a roll) and fittings. Wardflex is one name I recall. Installation is fast, but the fittings are expensive. Approved for all installations in this province....

If you must still exist in the 19 th. century, you can still screw bits of steel pipe together.....

Hope that helps;

10-17-2007, 12:47 AM
You do realise what propane will cost this winter huh?$89 once-vs-$89/week:eek:

10-17-2007, 03:43 AM
Wierd, Heating oil is going to be even worse - I heard of prediction of 35% increase in cost over last year, and last year was high to begin with.


Your Old Dog
10-17-2007, 07:01 AM
You do realise what propane will cost this winter huh?$89 once-vs-$89/week:eek:

Maybe I should buy me 2 or 3 more 100 pound tanks at $92.00 each from TSC and stock up on the gas before it goes out of site. I'd be surprised if I used more than 4 or 5 tanks over the winter. Hell, the savings in fuel would pay for the additional tanks. Of course, I'd have a yard full of propane tanks to mow around!!