That's not really an either/or question.

Oxy Propane is a high temperature, but localised flame, and can cause issues by melting tubes or tube plates if not used carefully while propane is a slightly cooler flame, but bigger and with a lot more heat capacity.

I would suggest that an oxy propane kit is something useful to have in the workshop for brazing as against silver soldering, but for more heat on a boiler a second propane is probably a better bet and is half the price of the oxy kit. Many of the older designs were produced on the understanding that paraffin blowlamps were to be used and these produced a flame similar to propane not oxy.

If you use a large propane bottle you may be able to get away with using a t-piece with both torches but if you use a small one a second bottle, or exchanging yours for the largest the rules your gas supplier allows might be an idea. A mate to hold the second torch is probably essential too. In my experience do not ask a significant other or partner – just don't ask me how I know!!

But before you try any of these suggestions what burner are you using? – the standard Sievert one is good, but they do a lot of others with far higher outputs and one of these may be the answer.

If you intend to silver solder your firebox stays a cyclone burner could be useful as well.

Edited By Nick Clarke 3 on 16/05/2021 15:26:51

+1. What's wanted is more kilowatts, not higher temperatures. A bigger torch producing more heat by burning more gas. Adding oxygen raises the flame temperature, which is good for cutting and welding, but the flame is too hot for solder and flux.

You might need a 38mm burner (12kw). Note bigger burners need bigger cylinders, 12kw will work off a 19kg bottle not smaller.

You can get vermiculite 9×4.5×1 blocks cheaply off ebay, I got 12 for £25. You can use them to block cold gaps.

Rockwool roof insulation is blowlamp proof if you can find it

Which Sievert burner were you thinking of, there, Dave? The only 38mm one I know is the soft flame burner intended for "cable work and other heat shrinking applications", and it is rated at 15KW.

For big heating jobs I use the Pro88 handle [with pilot flame] and one of the burners in the range 2942-2944. These are rated at 26KW, 43.5KW and 86KW.

I could do with a bigger pure propane burner myself, but for smaller hot jobs I use oxy-propane.
As mentioned above though, it produces a small hot flame for concentrated heat in one spot, but not quite hot enough for welding, where you need a fuel gas other than propane. It will happily melt holes in steel, so use with care.

Because of the cost of cylinder rental or deposit, I picked up a DeVilbliss medical oxygen concentrator, with a flow rate of up to about 5l/min; I think I paid £100.
This is plenty for a small heating torch, but not enough for cutting.

Mine came from ebay/Gumtree as the owner was moving up to a larger setup in a shared workshop.
It's a system favoured by those who make glass jewellery etc.

Tufnell Glass is a well known outfit, who can supply concentrators and torches etc.
https://www.tuffnellglass.com/contents/en-uk/d2.html

I'm using a small lead burner torch, that I had in stock anyway, as well as a conventional BOC torch.
I also bought some specific oxy-propane tips, again off ebay, and made adaptors to use them on the small torch.

Bill

Hi Peter, some good advice here. It is true the heat comes from the amount of gas burnt. The Sievert torch kit we sell comes with the 2941 burner producing 7.7Kw of heat. By changing your burner to 2941 you go up to 26Kw. There are a couple of bigger burners available, please ensure you have a long neck tube as it gets hot!! On the website http://www.cupalloys.co.uk we have a small video showing the flame profiles of a few burners. As Andrew says it is common practice to use the propane torch to get near to brazing temperature and then use a more precise torch, eg oxy/acetylene or oxy/mapp.

Hope this is of use.

Shaun.

Anyone spot my deliberate mistake? It's the 2942 burner that produces 26Kw.

One of the nice things about the cyclone burners [I only have the larger one – the 3525], apart from the way the flame wraps around objects up to a certain diameter, is their relative quietness; they emit a much more muted sound than standard burners of comparable size, so you can solder and hear yourself think at the same time.

Hopefully the 3525 is suited to your present job, Peter.

PS I have a 3525 cyclone burner which is about 10 kw, problem I find is that the heat is soaking away into the boiler as fast as it goes in, gets there eventually of course but still seems an awful lot of heat to put in to the whole boiler just get a few square mm up to temperature.

A friend on mine was perplexed at the logic of having to do this but he is a qualified welding engineer and has a lot of experience in the use of and the science behind methods like oxy acetylene, TIG welding etc.

Bill D.

Hi all,

Some good advice has already been given.

I use both propane and oxy/acetylene to make my boilers and help society friends with theirs. With the help of an assistant who provides a good amount of background heat with the propane torch, I then use the oxy / acetylene to bring the material up to heat locally at the point to be silver soldered. I have found this works for me as using a big propane torch tends to make everything very hot all at the same time. Also when using the method I've described I find it much more controllable. I have an account with BOC [usual disclaimers] and get my gases at very excellent rates . There is of course the monthly rental but this way offsets against the cost of having a boiler commercially made. Guess you pays your money and takes your chance.