What are the requirements for clearance and access?

[Robert Ellenberg]

I've designed houses starting back over 30 years ago and all have had the equipment in the attic, crawl, basement or occassionally the garage. I am now focused on smaller, tighter, energy efficient designs and putting all of the equipment and duct work in the condtioned space. I have also left the design of the HVAC system up to others but decided I needed to learn more so I've been studing the Mechanical System sections of the IRC which has raised some questions.

Section 13, General Mechanical Sustem Requirements, M1305.1.1, Central Furnaces, says that when they are in "compartments or alcoves", that you must have 3" of clearance on the sides and rear. However, it doesn't say how much room they must have if they are in mechanical rooms or ?? (neither can I find a definition for alcoves and compartments). But when you get to section 1402 on Central Furnaces, it says the clearance must be per the manufacturers specifications and makes no reference to location.

For access when a furnace is placed under a house, 1305.1.1 says you must have an access 30"Hx 22"W. But when you get to 1408 on vented floor furnaces it says there must be an access of 18x24.

Anyone care to give an explanation/clarification/interrpretation?

 

[Paul Sweet]

M1305.1.1 applies to furnaces in small mechanical closets, the exception allows lesser clearances as long as they meet the manufacturer's installation instructions.

I think that M1408 applies to the old floor furnaces that had one big grille where the return air came in around the perimeter and the hot air came out of the middle. http://www.empirecomfort.com/EMPIRECOMFORT/SpaceHeaters/spsub3.asp It doesn't apply to what we generally consider a furnace.

 

[Daddy-0-]

30x22 OR large enough to remove the largest piece of equipment whichever is bigger. Also need unobstructed path to the equipment and the equipment must be within a certain distance of the crawl door. (20 feet I think)