Reducing Manifold Gas Pressure

GMR

Hello all,

Just wanted to reach out to the gas heating experts out there.  What is your feeling about reducing the manifold pressure and adjusting the fan speed to achieve the proper temperature rise in order to reduce cycling?

Jamie Hall

Don't do it.

pecmsg

So, your unit is seriously oversized?
How old of a system?
LP or NG?
Moving more air will give you a cool heat and noised registers.
Without a combustion analyzer and the knowledge to use it I wouldn't do it!

GMR

I have a combustion analyser.  I would not be increasing the airflow, I would decrease it in order to maintain the minimum recommended temperature rise.

GMR

The system is Natural Gas

HomerJSmith

What is your altitude? I have come across furnaces that needed to be de-rated and weren't. Lennox had furnaces that the service instructions suggesting altitude de-rating being done by reducing the manifold pressure.

All the registers should be open and temperature rise checked.

Sometimes the temperature thermodiscs that are in the safety circuit need replacing.

EBEBRATT-Ed

You can usually go from 3.5" wc down to 3" wc without issue but not without a combustion test and make sure it lights properly