My brother-in-law and I are going to be finishing my basement. We just got the permit from the building inspector. When they returned my plans there was a note that told me to make sure furnace and hot water heater clearances were to manufacturer spec or 30". 30" seems like a lot so I headed to the manufacturer spec located on the furnace itself.

A Cude with 6 arrows, Pointing down labeled C, all directions but top labeled 0, top labeled 1 and a second arrow in front labeled 24.

Does this mean 0" clearance is required on all sides and 24" in the front if the furnace is going to be enclosed in a closet? Am I interpreting this right?

2 Answers 2


I would interpret the drawing as you did,however the inspector mentioned 30". I would verify that there is not a local code that requires 30". Another thought is that if you install it with a zero clearance and it requires service acess may be an issue unless your design allows for an acess panel. Also you want to take into account that at some point the furnace will need to replaced. You don't want to add demolition and reconstruction of the space to the cost of the furnace.

  • In most cases (I haven't read the code for every area), manufacturer instructions trump code. The 30" likely only applies if manufacturer instructions don't specify clearances.
    – Tester101
    Commented Apr 6, 2013 at 13:48
  • We are actually planning to leave the front and back of the furnace completely open. The left side is flush to my chimney. I am mostly worried about the wall that is going to be constructed against the right side. According to these requirements I can put that wall flush? Commented Apr 6, 2013 at 13:51

I would read it as: the minimum clearance to combustible materials. Its saying you don't have to have clearance on the sides and back and 24 in in front. Probably more a matter of service access than combustion, but a requirement, none-the-less.

I don't understand the "1" for the vertically oriented arrow (or the 'C', either), as the description says the vent clearance is 0.

I would say yes to a flush side wall, but as mikes mentioned, a bit (several inches) might be wise.

  • I believe the C means the furnace may be installed on a combustible floor. Commented Apr 9, 2013 at 13:05

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