# Negitive pressure HWT



## PlumberDave (Jan 4, 2009)

What HWT have you used in a cafe?

Been seeing a few issues with natural draft HWT's in negitive air pressure buildings melting pilot tubes wires the whole works. My only 2 ideas hav been stop the negitive pressure ie stop the range hood fans or cut some holes in the wall, or Replace the HWT with a Direct Vent powered or not.


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## uaplumber (Jun 16, 2008)

Add combustion air.


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## ILPlumber (Jun 17, 2008)

Unfortunately make-up air is often overlooked in construction. National gas code book is what I use for figuring make-up air.

I was just in a home the other day where they couldn't run their nice big range hood and have a fire in the fireplace. Fills the place with smoke rather quickly.


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## WestCoastPlumber (Jun 17, 2008)

combustion air is in our UPC code book. Combustion air is more important then alot of people think.


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## Tankless (Jun 12, 2008)

It sure is.....most commercial usually tend to be on the positive side...keep bugs /flys out. You need to make it so there is positive clean air combustable.....Get ahold of their HVAC guys and make them do it. With a comm. hood running they need to ballance it out.


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## PlumberDave (Jan 4, 2009)

Hey I like it everybody agrees. Fix the problem not the symptom. Turns out the hvac fresh air is supposed to have an interlock of some kind to the hood fans, this time.


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## Redwood (Sep 8, 2008)

This is a situation where they need much more than just a little balancing of the HVAC system. If they are not prepared to do it right I would walk away from this customer in a heartbeat.

Things like commercial kitchen hoods and paint booths exhaust huge amounts of air and require a special make up air unit to get rid of the negative pressure in the building. This negative pressure makes everything run oh so wrong creating the problems you have described. It can also create high levels of CO because of the draft problems.

If they are not willing to have an engineered makeup air system installed that interlocks with the range hood preventing operation of the range hood without the makeup air unit being on I would recommend letting them find another plumber.


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