Heating, Air Conditioning, Fridge, HVAC/gas hot water heater backdraft


QUESTION: Hi. I have a gas 40 gallon hot water heater that is back drafting. The vent duct rise is greater than 1/4 per foot. I have a high efficiency hvac and a 4inch chimney sleeve for the water heater.
It seems the back draft is due yo negative pressure in basement since I feel air coming from water heater vent duct from chimney. Also back draft resolves when I open basement window. What could be wrong with my set up or whet can I do to resolve.  Thanks in advance.

ANSWER: My guess is the a/c or furnace and the water heater share the same space in the basement?  Does the back draft stop if the a/c is turned off?  Is there anything else in the basement moves air from the basement to the outside, like a fan or clothes drier?


---------- FOLLOW-UP ----------

QUESTION: Hi thank you.yes the furnace is a high-efficiency and has separate intake and exhaust and there is a dryer in the same area.
However the back draft occurs when nothing else is running. We also have a radon mitigation system that is constantly on but that should be pulling air from under the basement slab. It sounds like there's a negative pressure in the basement caused by potentially many things so not sure how to address that. Do you have any suggestions of how to address that or is there some type of power vent for hot water heater's or something similar? Thanks

You can not add a fan or a damper to the existing water heater.  There are safety concerns with a damper and it was not designed to work with forced air.  They do make water heaters with induced flow on them.  They are suppose to be more efficient.  I am not sure if you are at a point where replacing what you have makes sense.  There could be several reasons for the backdraft.  Sitting here is a nearly impossible for me to give a solution to your problem.  There are websites out there that might give you some ideas.  


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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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