As long as there is no other 115 volt AC load that is definitely the simple and "code free" way of doing it.
But if the transformer is the only load there is no reason NOT to just use a "plug-in" transformer in the first place. The transformer can be a "wall wart" style - which IS designed to be plugged in and meets all the code requirements for a "plug-in" connection for all the chicken-littles worried about being code compliant.
Most likely a 24 volt unit - possibly an 18 volr - like a doorbell transformer. About 2 amps secondary. HTP2450 Honeywell is 2 amp 24 volt AC with thermal overload protection that plugs into any 15 amp NEMA outlet.
All NORMAL DPDT switches are break before make - some specialty switches are make before break. A DPDT "reversing duty" switch HAS to be break before make
No, but as gfretwell pointed out, most boiler wiring, or replacement boiler wiring is done without inspection, because there is already a C/O on the building wiring
Nec only plays one part in the central heating system safety. We have a variety of fire safety and life safety codes. In the area where the OP lives: all central heating systems need a disconnect "within sight from" the unit. This is an Nec rule. It means within sight of, and not more than 50 feet away. If the heating system is sitting in an open basement, there must be an additional disconnect at the top of the stairs to the basement. If there is a boiler room, the additional disconnect can be outside of the boiler room The idea is that the service man kills the switch that he can see, but if the unit shouldmalfunction, it can be killed without going near it.
Hot air heat has been around a long time, and works in all climates. I grew up with hot water radiators and thought them best. Mostly because I always noticed the furnace going on in houses with hot air. Hot water is dead quiet comparatively. Now that I have a house with hot air I wouldn't have it otherwise. No radiators getting in the way, and no window AC units blocking the light. No hanging water tubs on radiators to humidify when its dry. I got used to the furnace on/off cycle in about a week, and don't even notice it any more. If it cycles right, the heat is probably more even than hot water radiators, which are slow to respond to temp changes.
The switch has a stable third state/position, in the center, where the commons aren't connected to either of the sides.
No. There are cases where you don't want an interruption between switching from one to the other. Obviously, a switch with a "center off" is also break-before-make.
It would IF there are ANY of those safety devices currently installed or required, and they are "upstream" of the main power connection. Most today, I imagine, would be low voltage controls wired out from the main control box.
Correspondence with an electrical contractor in Central Texas, another electrical/heating contractor in Albuquerque, and another in Palmer Alaska all indicate it is "common practice" to have the furnace connected by a twist-lock plug to a receptacle. An electrician in Central PA says they do it all the time - it IS against code but the inspectors all allow it.
The reason given for not allowing it is flexible cords did not stand up to the temperatures that could be expected in the furnace wiring cabinet. Flexible cords are used on electric space heaters and other heating appliances - so high temperature cord is available - and used.
Umm, No, they would not be low voltage controls wired out from the box...
The "Emergency Shut-Off Switch" is a normal single pole lighting switch installed in a remote location usually with a red switch plate, so that the heating plant can be shut down without needing to enter the basement in the event of a fire or CO leakage condition...
The "firematic" is a safety device mounted in an outlet box directly above the heating plant which will automatically break the 120v circuit in the event the temperature gets too hot which happens when things catch on fire...
Both of these devices are required in many places to be installed between the power supply at the circuit breaker and the service kill switch mounted on the side of the unit... Even *if* you installed a switched outlet to use a cord set to connect the heating plant to a gen set at the heating device, you would eliminate all of those safety devices from the circuit when running the heating plant off a generator...
Why do people see the need to do things in such over complicated ways ? If all you are concerned with is using your heating boiler during a power failure, the single circuit transfer switch at the power panel is ideal -- no lengthy extension cords all over the house leading from the boiler to outside where the generator is located... The OP could install one of those rather easily and not have to worry, with multiple circuit type transfer switches there is usually an option available with the kit to hard wire the link from the transfer switch to an outlet outside for a short cord from the generator to the hard wired outlet point rather than laying out long runs of extension cords...
Not only would installing the transfer switch equipment and dedicated outlet/hard wired link for the generator make more sense, a generator outside with a short cord on it is a less desirable target... You could pour a small slab like you might see under an air conditioning heat pump with a large size eye bolt set in it so that you could use a padlock and chain to secure the generator in place while it is being used...
I'm not convinced that putting a plug and cord on a gas furnace is unsafe. Yah, I know, Barney Fife says it violates some NEC rule but is it actually unsafe?
Besides, most of us are not exactly flush with cash right now.
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