910.4 Clearance below the furnace
The lowest portion of the furnace is at least 6 inches above grade. Section 910.4 permits a reduction to not less than 2 inches only where the manufacturer has sealed the lower 6 inches of the furnace against water entry. Confirm that construction on the selected unit before using the reduced dimension.
If the required vertical clearance is unavailable, excavate beneath and around the unit to form a pit that provides it. Show the actual grade and pit on a section, rather than relying on a plan note.
910.4 Side and control access
Provide at least 12 inches on all sides and at least 18 inches on the control side. The control-side dimension preserves access for adjustment and service, so orient the selected unit before detailing the pit or adjacent foundation elements.
What changes in the field
A crawlspace with enough nominal depth can still fail once the furnace body, grade, water exposure and service envelope are drawn together. Review a section through the actual selected model before permit.
Field check
Draw the lowest part of the unit against actual grade.
Dimension all sides, especially the control side.
Show an excavated pit where the available depth does not meet the required clearance.
Where to show it
Furnace section
Crawlspace or foundation plan
Model installation data
Code basis
2024 IMC Sections 910.4 model-code education. Confirm the locally adopted edition and amendments, the selected product listing and manufacturer instructions, and the authority having jurisdiction. Read the ICC 2024 IMC Chapter 9 for the complete model-code provisions.