Q on clearance requirement for retrofit wood furnace

[motoguy]

Managed to move the Kuuma from it's storage area in a spare room, to it's new location today. Didn't hook up the flue, but did a test fit. Happy with it.

Which brings me to ducting. The Kuuma is located in our walk out basement. The trunk line runs in the center of the house, the length of the house. Branches exit the trunk at 90 degrees, straight to the registers. The trunk is insulated metal, branches are insulated flex ducting, located between joists for the upstairs flooring. Basement ceiling is unfinished.

Ducting from the Kuuma to my existing trunk won't be an issue. This flex ducting...may be. Specifically, the wiring that runs between the joists (perpendicular to joists). In several places the flex ducting is pressed against, or in some places between, electrical runs (Romex). Not an issue currently, but likely more so when replaced with rigid metal ducting.

So...this 1” to combustibles requirement...if I need to squeeze round metal ducting between wires, or against wires, can I just put a barrier there? 1" of some type of high-temp insulation? Is that acceptable, as it gives a 1" barrier from pipe to (I assume combustible) Romex? Does code require a 1" -air- barrier?

If I can do something like that, replacing all this flex tube won't be too big a deal. If I have to arrange a 1” air gap between duct and Romex...life might suck.

The plenum from the wood furnace will rise 3-4 feet, then run horizontally 10' or so before going through a wall (easy to make clearance), then make a 90 degree turn and run another 17' or so before it connects to the existing plenum for the propane furnace. It as at that point it will enter the main trunk for distribution.

Ideas?

While not my home, this is the type of thing I'm talking about. Romex spanning joists, perpendicular to the joist direction. They are not all at the same height, so the existing flex snakes "up and down" through them. No "turns" left or right...just straight runs.

 

[kingOFgEEEks]

I'm not an expert on this, but I believe that you are going to want to lower your main trunk so that the branch ducts don't have to dip and dive around these lines anyway. Going to a wood furnace means you want the heat to gravity flow, and not have to rely on the fan all the time.

Think drainage PVC plumbing, in reverse.

 

[motoguy]

Trunk line is located below the joists (running perpendicular to joists). Branch lines run between the joists (parallel with joists), so branch lines are already above the trunk line at all locations.

 

[blades]

From what I remember , first hot side ten feet of ducting off solid fuel unit is 2" clearance , after that 1" , must be metallic ducts, if insulated ducts I think there is also a spec for that, I wouldn't want that plastic wire riding on the ducts directly.

 

[Oldman47]

Welcome to the forum motoguy. I am afraid life will suck. No way do you want to get too close to that 14 gauge electrical wiring with a hot exhaust from your stove. Even if you do not manage to ignite the wiring, just melting the insulation on it will be a major problem for you. Modern wiring, the kind that shows up in all of the warnings on lighting fixtures, is only rated to 90ºC, 194ºF. That is not the maximum temperature of the outside. It is the maximum temperature of the wire in whatever location it has to live. If you run a hot air duct past that touches the outside and is a mild 160F, that does not leave much capacity for the electrical load to use up. Assumptions in wire and motor ratings are that ambient temperatures are 40ºC, 104ºF. Yes, that is quite warm but not nearly as warm as a warm air duct. I would suggest that it would probably be easier to reroute the electrical wiring than to avoid it completely with new duct work.