Distance Between Exhaust and Intake

[DrRTU]

Design as per ASHRAE 2007 (no addenda). If a unitary RTU with gas heating has a barometric relief or power exhaust. RTU is less than 400O CFM. What do you see as the minimum separation of exhaust or flue on RTU and its air intake hood. I have extended the FAIs 10 feet. "Other" designer is stating 15' Exhaust / relief air does not contain any hazards. Not process.

 

[ProcessHVAC]

What do you mean by ASHRAE 2007? Check your local building code, natural gas/propane codes.

 

[DrRTU]

Sorry left out the important ASHRAE 62.1

 

[EnergyProfessional]

check code and triple that at least.... take into account prevailing wind, and obstructions etc.

and do you need separation between the gas-fired RTU exhaust and the fresh-air intake? If so, warm exhaust rises, so vent that to above the air intake.

I've seen many installations where the plumbing venting stack was separated from air intake per code (code doesn't use actual obstacles, etc, just distance) and nuisance complaints required relocation of the plumbing stack. So meeting code alone may not suffice....

 

[KiwiMace]

My old US company used to cookie cutter an exhaust extension up above the unit to add a bit of distance and reduce the chance of the exhaust being entrained in the OA. Rectangular SS duct with a drain hole.

 

[DrRTU]

I don’t understand how a unitary manufacture can sell a rooftop with gas heating based upon compliance with ASHRAE 62.1. or IMC chapter 4. I understand, the design is a “system” installation and not an equipment installation. ASHRAE 62.1-2007 reads as follows: table 5-1 - air intake separation distance is listed at a minimum of 15’ from “vents, chimneys, and flues from combustion appliances and equipment (note 4)”. Note 4 “reads shorter separation distances are permitted when determined in accordance with (a) chapter 7 of ansi z223.1/nfpa 54-2002 for fuel burning appliances and equipment (b) chapter 6 of nfpa 31-2001 for oil burning, (c) chapter 7 of nfpa 21-2003 for other combustion appliances and equipment”. I believe nfpa 54-2002 requires a vertical separation of 36” of the flue above FAI. Most equipment mfgs have an accessory flue extension kits but the delta height does not meet the 36” rule. This issue is NOT limited to ASHRAE 62.1., IMC 2009 401.4.3 reads “Intake openings shall be located not less than 3 feet below contaminated source where such sources are located within 10 feet of the opening. Thus a gas heating RTU requires a minimum delta height between the FAI and flue or 36” or 10’ feet away from flue. I can count hundreds of RTUs I have seen that do not meet these requirements. Have others used different wording of an ansi/nfpa document to justify not having a delta height of 36” or FAI 10’ away from a combustion flue? Thank you.