I don't have the code book to refer to, but from another site: "Here's what the Cdn code says, which applies to you, Pelican. Each gas furnace must have its own 15A circuit and disconnect. The breaker at the panel can serve as the disconnect if the panel is located between the furnace and the escape route. That means, if in walking away from the furnace towards your escape route you pass the panel, then you can use the breaker as your disconnect. If not, a disconnect switch is required between the furnace and escape route. It doesn't matter how you wire the switch. The loomex feed wire must be inside
7/16" flex conduit if the feed is less than 1.5m above the floor or when the loomex is subject to mechanical damage. You must bond the grounding conductor (bare) in the supply cable to the bonding terminal in the furnace connection box. Any competent furnace service person would always check the supply cable for power before servicing, regardless of the position of the disconnect switch."Also found this: "My 1981 NEC Handbook makes no mention of this, but my 1993 NEC says that central heating equipment should be on a separate circuit, but associated equipment, like pumps, humidifiers, or electrostatic air cleaners may also be on that circuit. See Article 422-7 in the '93 Code. It's also not marked in the '93 code as being a new change, so in 84, 87, or 90 this section was added. Before that, the furnace apparently could be on a shared circuit, and a separate fuse or breaker would be useful. My furnace, fairly new, installed on a shared circuit, has a 12A Fusetron in the disconnect switch box mounted on the furnace itself. The installation was a kludge, so I was going to rewire it, and now will do so on a dedicated circuit. "
All I know for sure is for at least the last 20 years it has been MANDATORY in Waterloo Region, Ontario Canada, that a furnace be on a dedicated circuit and that if the service panel is more than 15 feet from the furnace, and not in the direct escape route from the furnace, that a disconect switch must be provided as close to the furnace as is practical, and the wiring to the furnace must be via metallic sheathed cable (AKA BX) supported on a rigid structure from the ceiling (can be strapped to gas pipe) IIRC that shutoff switch must be in the same room as the furnace, and a safety lockout tab is highly recommended (so no-one can accidentally turn the furnace on while it is being serviced) Seem to remember that is mandatory if the switch is outside the furnace room/enclosure.