A blowlamp is not too fierce. It depends on the lamp and the way in which you use it, either way it is far more controllable for the majority of soft and silver soldering jobs.
I have now put together my plany of boiler, engine, gas tank, seperator, water pump and all pipework and it has all been assembled with silver solder and a blowlamp. The most important factor is control and to give you that control you need a good working area that will maintain the temperature.
I use a number of small, very lightweight bricks, obtainable from most shows and suppliers, and arrange them into a small hearth. You have to think for each job how the heat is going to dissipate and then prevent it from doing so. If you put your copper pipe in the vice for instance the heat will go straight into the vice and you will never get it hot enough. If you put it into a little drilled hole in your fire brick the brick will prevent the heat loss and the pipe will heat up and stay hot considerably easier. If you put another brick behind it to prevent any radiation losses as well you will transform the whole process.
All my brass fittings were silver soldered to the copper pipe using these type of techniques. For very small work I use a very small petrol blow lamp, which is very handy and for anything bigger I use the B&Q type of blow torch with the appropriate nozzle fitted. You can easily control the flame to suit the job and after a bit of practise you will be turning the flame up and down as you need while you are applying the rod with the other hand. I usually aim the flame at the brass fitting to get the heat into that in the knowledge that the copper pipe will be already up to temperature as soon as the brass is. If you aim the flame at the copper pipe the brass fitting will never get up to temperature.
If you want to use an iron you will not be able to use silver solder and even for soft solder it is more of a struggle to get the temperature into the parts evenly. For a steam plant I would highly recommend a blowtorch and silver solder rods with a flux coating as this will give you a much stronger and higher heat resisting joint.
Colin hit the nail on the head when he said that soldering is really very simple if you think about what is happening and apply a few very basic laws of physics. When you get it right all you have to do is rub off the flux with a bit of wet and dry, polish with a bit of brasso and you will amaze yourself at what a neat proffessional job you can achieve.
