One contractor said it would be difficult to get the normal pitch for the intake and exhaust pvc pipes for a 90% furnace. Another said that the pipes could run uphill to about halfway to the outside wall and then could run downhill to the outside wall. The second contractor said the only reason for the pitch is to prevent water from sitting in a low spot and that it didn't matter which way the fluid ran. Is this true?
Does the exhaust motor run for a few seconds after the burners shut down to clear the exhaust pipe of combustion gas or will this shallow inverted "v" setup trap exhaust at the apex or worse yet let exhaust fumes back into the furnace?
I also have a limited choice of where the intake and exhaust pipes can leave the house. There is a on that outside wall a nearby electric meter as well as a dryer vent. What problems could occur if the exhaust fumes get pulled into the intake other that reducing the supply of oxygen to the furnace.
I haven't been able to get a good answer why the exhaust or the intake shouldn't be near the electric meter. Also is it a problem for the exhaust pipe to be near the dryer vent and why?