You're interpreting NEC 440.8 correctly, and it's a good catch on the attic scenario. Let's break down the nuances: NEC 440.8 and the 8-Foot Rule

This section of the National Electrical Code (NEC) deals with the clearance requirements for air-conditioning and refrigeration equipment. The intent is to prevent electrical shock hazards in areas with water. The 8-foot distance (measured horizontally) is a safety buffer.

Attic Above a Tub/Shower

If an AC unit (or parts thereof) is directly above a tub or shower in an attic, and any part of it is less than 8 feet horizontally from the edge of the tub/shower, it would indeed violate NEC 440.8. This is a common oversight.

Bathroom/Furnace Closet Sharing a Wall

This is where it gets a little more nuanced. Here's how to assess it:

Penetration

If the furnace closet is fully enclosed (walls, floor, and ceiling) and the wall separating it from the bathroom doesn't have any penetrations (holes, vents, etc.) that could allow moisture into the furnace closet, then technically, NEC 440.8 might not apply as strictly. The furnace is in its own dry environment.

Direct Contact

Even with a shared wall, you need to be mindful of the 8 ft rule. If there is anything on the Furnace that can be touched from a person in the tub or shower that is less than 8ft away, you still have a violation.

Local Amendments and Interpretations

Keep in mind that local jurisdictions can amend the NEC. Some might have stricter interpretations or specific rules regarding shared walls and clearances in these situations. It's always best to check with your local electrical inspector or building department.

General Considerations



Moisture and Condensation

Even if you technically meet the code, consider the potential for moisture and condensation from the bathroom to affect the furnace. High humidity can cause corrosion and other problems. A good vapor barrier and adequate ventilation are crucial.

Service Access

Ensure that any maintenance or repair of the furnace can be done safely without any risk of contact with water sources.

Alternative Locations

Whenever possible, explore alternative locations for the furnace or AC unit that avoid these potential conflicts altogether.

In conclusion: While a shared wall could* be permissible if the furnace closet is a sealed, dry environment, it's a situation that requires careful evaluation, clear separation, and consultation with local authorities. The safest course of action is generally to avoid these configurations whenever feasible. Flag for review