Which gas should I solder roof flashings with?
Completely adequate and acceptable soldering of seams can be achieved using a variety of methods. Hand irons, propane fueled, or acetylene fueled irons are all fully capable of producing long lasting watertight results. However, there may be reasons to suggest using one over another under certain circumstances and this will be covered below. It’s worth nothing, if you have spent your career soldering with charcoal pots and hand coppers, upgrading to a gas fueled iron will be like upgrading from a bicycle to a Tesla.
Difference in Gases
Output Temperatures – The flame temperature of propane vs. acetylene is the main factor that is considered when choosing a gas for soldering
Propane flame temperature: 3596°F
Acetylene flame temperature: 4622°F
Acetylene burns over 1000°F hotter than propane! Note that oxy acetylene combinations burn significantly hotter (5612°F) and should not be used for soldering copper as this is above coppers melting temperature (1984°F). Remember that although the flame temperatures are high, they are being applied to a copper piece that is then transferring heat to material being soldered, therefore, the exact numbers are not as important as the understanding that acetylene burns hotter than propane.
Availability to users – Propane is readily available to anyone over the age of 18 at many common supply stores like Home Depot and Lowes. You can buy a variety tank sizes including portable canisters for relatively cheap prices. Acetylene requires seeking a welding/gas supply store to purchase and will be more expensive.
Safety/Cleanliness – Without getting into the arguments over why one gas may or may not be more dangerous than another, it is fair to say that serious care should be taken when handling either gas but the general public is much more familiar with propane. Acetylene is a less stable gas with a wider range of combustibility. All tanks need to be transported upright.
The climate that you are generally working in is worth considering when making a decision on a soldering iron. If you are frequently going to be in colder field conditions and wintry temperatures, then acetylene torches may be the better choice. In windy and cold conditions you are going to want to make sure that the copper tip is getting ample heat. It is beneficial to rely of on a heavier copper tip when working in colder temperatures. Aero Acetylene torches recommend using their 1.25lb copper in temperatures at or below 45°F.
Level of Experience
Novice – If you are a DIY solderer and have little or no experience, the Express Propane Soldering units would be the direction to go. They are user friendly, reasonably priced, and will give you the tools to get professional results with minimal practice.
Experienced – The acetylene irons would be more geared to roofers who are more familiar with gas. This isn’t to say that there are not many of professionals out there who solder expertly with propane.
As stated above, for first time users, stick with a propane soldering kit like the one below and you should be able to get good results quickly. Unless you are experiencing heat issues with a soldering iron, there is no need to swap from a propane to an acetylene iron. For professional crews that are working year round in various conditions and want to go acetylene, the Aero Duplex torch is the obvious choice.