This is the age of the DIY homeowner, to be sure. However, there are still skills that are out of most people's leagues. Help with your furnace is an area that definitely falls under "do not do the whole thing yourself." Here are at least four good reasons why you should hire a heating contractor when you need help with your furnace.
Heating Conversions Are Complicated and Dangerous
If you are trying to convert electric heat to gas heat, or oil heat to electric heat, you have quite the tall work order in front of you. Conversions from one type of heating to the other require not just the removal and installation of a different furnace, but also different electrical wiring, pipe installations (when applicable) and fuel connections. It is not simply a removal and reinstallation process by any means, and making a mistake could result in ignition, fires, and even explosions. No amount of DIY pride is worth your life.
Welding Skills May Be Required
Most DIY homeowners do not have welding skills. Even if you understand how welding works, you technically should not be performing any welding yourself because it could void some part of your homeowner's insurance (i.e., you did something without a license and it caused extensive damage to your house which insurance will not cover). Soldering is one thing because it is not as dangerous as welding, but if you need a welder, your contractor should manage that.
You May Accidentally Install the Furnace Backwards
Let's say you go ahead and install your new furnace anyway. With an oil or propane furnace, there is little guessing involved because you know which direction the furnace has to face in order to connect to the fuel line. However, it is quite possible to install an electric furnace backwards. Now your cold air exchange vents pump out hot air and your hot air vents are blowing cold. Since you have the vents soldered on (or worse, welded), you now have to cut through the attached ventilation shafts and turn it all around. The heating contractor could make sure you avoid these kinds of mistakes.
Repairs Require Technical, Mechanical and Functional Knowledge
You probably do not have technical, mechanical, or functional knowledge regarding furnaces and heating. That said, performing repairs could cause just as much damage as attempting a DIY furnace conversion (see above). Call the heating contractor for any repairs instead, at least until you know a lot about furnaces.