furnace or boiler?
furnace or boiler?
If it's a furnace, I'll reserve comment. I usually see hot water boilers in the large sizes. The question is how much is factory wired and ships in one piece. Just bringing a feed to it may not work. You will have to know sequence of operation and wire in the external limits, accessory equipment, and zone controls.
If it's a boiler it's likely a cast iron sectional type and ships in pieces. Nothing except the burner will be prewired ... and there's no wiring digram that shows how every limit and pump control gets wired. I've done a ton of them. The limits will be hanging on the boiler, operating control, lwco, high limit, hot water reset - heat timer, gas train, combustion air. Each boiler is pretty much a custom wiring diagram depending on the trim and accessory equipment.
I've bid boilers very competitively for $3000 and the prime would find someone who has not done them before to wire for $800. caveat.
It's very easy to break boilers with thermal shock. I get called all the time to look at boilers wired by others. If it's a boiler you should know what thermal shock and flue gas condensation is ... before you cause it. Steam boilers have a condensate pump feedwater control.