Diagnosing negative pressure problem

[timma100]

this has been an issue since I purchased the home two years ago. Anytime the HVAC turns on a significant amount of air is drawn into the home from the attic through open back ceiling lights, cracks in the windows, and the chimney if the flue is open.. there’s enough flow, that if you had fire lit and turned the HVAC on the fire and smoke is drawn into the home.. I have inspected all the ducting in the attic and found no cuts or disconnected registers.. the only item left is the unit itself which is roof mounted.. any suggestions to diagnose this issue or should I just call an HVAC company at this point?

 

[Snoonyb]

It sounds like your system is not balanced, so I would have an HVAC service co. do that, and it could be something a simple as adding restrictors, in the way of filters, in your return air registers.

 

[timma100]

It sounds like your system is not balanced, so I would have an HVAC service co. do that, and it could be something a simple as adding restrictors, in the way of filters, in your return air registers.

You make a great point. The previous owner installed a 4Ton /1600 CFM HVAC unit. Considering this is a 1650 square foot house, it’s oversized. Originally they had a .5” thick 14x30 return filter, which restricted the flow so much the expansion coil would freeze during the summer. I’ve moved to a 4” thick return filter of the same 14X30 dimension. In both cases, a strong draft was felt coming from light fixtures when the hvac was on. In the mean time I’ll open all registers in the home to hopefully reduce the back pressure supply side…

 

[Snoonyb]

The service co. can adjust your air changes per hour ratio, which is commonly 4 to 5.