More of a mechanical design question:

My reno presents some interesting challenges regarding the duct work where I’m avoiding vertical chases and bulkheads for ductwork.

I’m doing a 4 zone, low velocity forced air system.

Doing the pressure calcs, specifically the 3rd floor zone I’m getting around 0.7″w.c. Based on the Lennox unit I want, the specs say the max is 1″w.c.

Where I’m afraid is I’ve never installed a furnace on a system like this. So I was wondering if anyone as any experience in this regard of pressure drop of a duct system and unit performance (or issues)

Is 0.3″w.c. a good buffer for pressure?
Can I go right up to 1″w.c. without any issues?
Is there a standard practice pressure value I should be going by?

Thanks,

Jamie