Well, it depends on how long you want to run and how much heat you want to produce. See http://www.flameengineering.com/Red_Dragon_Propane_Torch_K.html regarding both vapor and liquid withdrawal systems. What do you consider to be a "small" blacktop repair? How much ice do you typically need to melt? Are you using a 100# propane tank (or larger)?

I have found that running a 500,000 btu torch will go through a 20# tank fairly quickly and will generate ice on the outside (resulting in reduced pressure) when running wide open. It'll work, but for just a short time. I typically use 50# tanks.

The more expensive models are appropriate for extended run times and subzero temperatures.

Thanks for the reply.
Red Dragon looks like quality stuff.
I expect to have to occasionally melt ice in about 40 feet of 8-inch foot-deep trench -- it won't be solid, of course -- probably an inch or two thick. If this one job would rquire a significantly larger/heavier burner, I could deal with it in other ways.
I'll have to melt a walkway across maybe 30 feet of blacktop and concrete.
Blacktop repairs would be at most a seven-foot long half-inch crack -- I have a number of those -- and some small patches -- a foot square or less.
I also expect to use the thing in several acres of woods (wetlands, safe enough for flame) to try to hold back greenbriar that's choking paths. Might also burn along the base of some welded wire fence.
For the in-the-woods stuff I'd need a tank I could carry, and given my physical decrepitude, that would probably mean 20# tops.
And then there's the light weed duty in my wife's flower and rock gardens. Maybe I need a little one for this and a bigger one for the other stuff -- I'm on a tight budget but if that's what it's gotta be ...
Thanks much for any advice you can give.
rr

"Several acres of woods"
You qualify for our discount rental of a propane delivery truck - just hook up the truck hose and flame on.
I find that a 50# is the largest size that I can carry with just a bit of difficulty. Get an engine-powered wheelbarrow since some of the terrain is likely uphill.
Continue your enrollment in weight training.

y'know, altho you're kidding, you've suggested something that would work. I have a Gravely that could easily carry a 100-pound tank into some pretty tight and rocky places.
It's beginning to sound like I can't afford the propane, tho. Ah, well. Rotary plow to bust up the ice in the trench, brush hog for the woods.
Thanks for giving me something to think about.
rr

Northern (Hydraulics-formerly) Products had a 100,000 Btu unit for about $50, and a 500,000 for about $65. If you figure in the shipping, the 500K unit will also make 100K Btu on "low"
I tried it for weeds poking through cracks in blacktop- it fried the tar off the blacktop and the weeds came back anyway. I wasn't impressed with that. It does make heat like crazy though- it's over 5 times what my furnace puts out, and on a low-ish setting- it will start any pile of sticks, etc burning in a few minutes. I've never had it up all the way. I got tired of throwing kerosene, gasoline, etc on woodpiles to get them going. This is really why I bought it.
I did heat a 24 x 30 x 9 foot garage from 17 degrees to 55 degrees in just over 10 minutes-
1)remove one of the cars
2)wear earplugs
3)prop the torch up on a ladder -don't leave it unattended- 4)raise one door about 3 feet for oxygen.
5)keep the torch about a foot off the floor and about 6 feet
from anything else
6)flame size about 12-16 inches by 4-5 inches.
This allowed us to get the sheet rock done and dry the
spackle.

A hunting cabin friend uses his propane torch in a cheap
oil-drum stove (with a 6' flue) to heat his shed. It gets
toasty fast, doesn't stink, is much easier than wood to start and control and clean up after.
Think before you light!

Thanks Fred. I'm about ready to get one of these things and I could definitely put it to the use you mention. I'll look for that model.
rr

to RKCR123,
If I'm not mistaken, the 500kBtu burner I got from Northern (tools & equipment) products is the brand you mention above..
If you don't open the valve all the way, it's less likely to freeze up, but I' hve only opened it up so see what it'll do.
It's a roaring blue obscenity is what it is. The stars were just coming out... It was a calm and peaceful moment, at first. My 600 foot distant neighbors were on their deck and called over to ask if I was alright! (Told 'em I had gas)
But seriously, this size should be all you'd need. I light it with a smaller propane torch, or a welder's igniter.
One trick, though, is the newer propane tanks have a safety
feature that will not allow gas to flow if there's no resistance when you open the tank valve- so you need to remember to close the torch valve first. If the tank safety
valve does lock up, you need to disconnect the torch's gas
fitting from the tank,( This lets the hose, fittings, etc de-pressurize. ) then re-connect with the torch valve closed. I hope they (the propane tank mfg'ers) did this to keep people like me from making REALLY big flames with the
tank nozzle.
I think you mentioned burning weeds with it. I found this
option to be more trouble than it's worth- you over heat a fence wire and it'll rust really fast, If there was any vinyl coating, that goes away fast, too. It will temporarily
"kill" weeds but they grow right back. If you think of nature's occasional torching operations- most of the small
stuff grows back pretty quickly, depending on the season. You REALLY DON'T want to burn poison ivy or poison sumac- the smoke and vapor is bad news in your lungs, throat, nose, eyes. If you do burn that stuff, stay out of the fumes!
The other issue is fires getting out of control. Controlled burn conditions can get pretty uncontrolled if a wind kicks up.
I did just use mine to burn the seeding tops off of some nasty little plants that make burrs that stick to my dog. The plant tops were sticking out of about 10" of icy snow and I fried them off and burned (hopefully) next year's
crop of seeds. At least, the ones I found. A weed whacker,
a professional type one, will deal with weeds much more easily and maybe more effectively than the flame-thrower.
But, you can't heat a garage with a weed whacker. good luck.

I bought a weed burner about 5 years ago for around $60. I hooked it to a standard gas grill size tank and put the tank in a small lawn cart. We thought it'd be great to kill off grass and weeds that grow down the middle of our long gravel drive. It did kill off the top growth, but the grass and weed roots seemed to thrive as they resprouted! (Remember in years past when people would burn off fields and even lawns to encourage new growth the following Spring?) Same thing here. While it might work for patching blacktop, I'd say save your money if you think a weed burner will permanently eradicate weeds or grass!

Thanks for the info. It's kinda crappy that the manufacturers seem to want you to believe they'll do weeds in permanently -- I knew that wasn't easy but thought maybe the gentle overheating made a difference.
rr

The main use of mine is... starting bonfires on the beach! And I have to say it does a great job of igniting soggy driftwood.

Has anyone tried using one as a zamboni?

Dan

Have any of you tried using a 100,000 BTU model to gas gophers by sticking the end of the torch down a hole with the gas on but without lighting it?

That idea reminds me of the Rodenator.

MM

This link lets you view the movie, "The Return of the Saber-Toothed Gopher". It's not for the squeamish, but I don't know what its rating is.

MM

Not that it really matters, (if you have a torch and it does the job you need it to....then it does the job you need it to), but you won't get anywhere near 500,000 BTUs of output from a portable tank. There are charts all over the 'net showing how many BTUs are available from different size tanks when the ambient temperature is at a certain level.

Here's one such chart right on the Red Dragon site. For instance if you have a FULL 100 lb. cylinder, and the ambient temperature is 40 degrees F, then the maximum continuous BTU production you can expect is 214,000 BTUs.

We get calls all winter long about jobsite heaters that are "broken" or "not keeping the building warm", and most often the cause is a vastly undersized propane supply. Even when the heaters belong to the customers themselves, they call and want them "fixed". They've often tested the heaters on their own in the off-season using the gas supply at their own shop or warehouse.....when the ambient temp at the tank is in the 60's or 70's.

;-)

Here is a link that might be useful: BTU capacity at various ambient temperatures

Works great on long narrow garden rows, patching roads when it's really cold. I also use it to light a fire under my crews ass. Lol do get a longer hose and a bigger tank. Get at dim weeds! Remember this is war and you are not a wimp. If your worried about fire have a water hose ready. Keep knocking the weeds back, it takes a few times to get a handle on the weeds.