NEGATIVE PRESSURE ON FAN DISCHARGE

Jackmartin

Well, I posted a question as to how I could have a negative on the supply side of the fan. I think this is important enough to post again. I have never in 43 years see this happen. The negative at the fan discharge was -1 and the suction was-15 for the return. The house is 4 years old I am usually working on something a 100 years older. I decided to ask my eldest son, he is a P.Eng and of course he knew what was wrong immediately, sigh. He sat me down, got out his calculator ,asked if there was another fan on the system and I told him the owner has a large HRV. He then explained the HRV fan was cross connected to the supply air duct work. He did the ratio math and showed me how even a slight suction on the supply side could cause a negative ( albeit) small to occur, duh. This customer has not been able to have his electric heat come on for four years because the previous contractors never did a manometer test. They kept putting the positive static tube in the supply and the air proving switch of course saw a negative and refused to complete. We installed an A 303 Dwyer static air tube in the return ,hooked the air proving switch to negative and what do you know ,he has heat. He is also complaining of very low humidity, this is the exact opposite of most claims here ,in a house with a very high insulation vapor encapsulation,usually they have too much humidity. This hooking of the HRV to the supply would also effect his humidity readings, last year he had a humidity reading of 15% no wonder everyone had nose bleeds. All the best Jack

Jamie Hall

Thank you -- yet another bit of wisdom from the Wall!

EBEBRATT-Ed

That explains that. I was loosing sleep over that one!!