Besides just being old, will a new gas boiler be more efficient, is it safer? What brand or how do I choose? Where should I get it? Should I hire my next door neighbor who does HVAC for a living? (I don't know if he does good work or not. Not much info on Angie's list in my area.) Could/should I install it myself? I'm not afraid - unless you say I should be. :) I have 4 programmable zones and valves. Also - should I be doing any maintenance on this boiler or a new one?
A few points to make: A 45 year old boiler (with an expected life of around 50 years is about at the end of its useful life. Further to that, it will be very inefficient relative to new units. So, you are facing a new installation shortly in any case. If you can sweat large pipe, use large pipe wrenches and know how to measure fittings, installing a boiler, even one of the new high-efficiency units is not rocket-science. At the same time, many manufacturers will not honor their full warranties unless a unit is installed by an approved technician. So check that. I have installed several boilers, but I always had a plumber friend check my work and sign off for the warranty. Again, there is nothing special about it other than the size of the pipe and fittings and the weights. Maintenance requirements for boilers is fairly limited - make sure the water chemistry is OK - the burners and boiler sections are clean and the controls are working properly. Make sure your circulator pump(s) are lubricated if need be. Good luck with it.
If it is still working, I would get the gas company or contractors to give an estimate of cost and projected efficiency savings. Then decide whether to replace and then decide whether to do it yourself. Check out the needs for permits and inspections and whether you can legally do it yourself.
Newer furnaces tend to be more efficient. Are you using natural gas or propane? I would have 2 or 3 different HVAC people come in and give you an estimate. They will each recommend what to get.
