Home had a 3 year old high efficiency Lennox furnace.
The intake vent was closed. What damage can occur to the system with running the furnace without the proper intake air?
The intake had a duct damper control. It stated below with a sharpie that this should be closed in the summer. The hole intake vent seemed strange. PVC exhaust but a insulated flex duct intake. With a damper. I see this as a problem because the home owner may leave closed. Like this one.
Thanks
This is based on my furnace.
If the flue fan does not develop enough discharge pressure( an indication of its full operation) then no gas/flame/etc. So if the the intake is shut, then the fan cannot move any air, so the pressure switch will not allow the furnace to continue operating. I’m guessing after a few short cycles the home owner will remember what went wrong, or pay someone to reopen the valve.
As for the insulation, it makes sense. Cold air is coming in, allowing for condensation to develop on the piping. The insulation will allow for the minimization of the condensation.
Just guessing…
tom
Speaking of insulation. Why would you insulate the main DWV platic stack?
You can see the stack in the backround & it is wrapped with insulation & plastic. Seems like a waste. A waste stack that is.
Man hijacking your own thread. 
Was there any copper piping in the area, could be a heat recovery heat exchanger over there. And that was some person’s handyman work.
tom
You would insulate the drain stack to reduce the sound of running “water”
If the primary return air is sized properly having the outside air duct closed it would have no bearing on units operation. I would leave it closed if its not filtered unless its a business and required. If you bring out side air in to the house with out exhausting it it cause the house to become pressurized and is not very efficient. If you really want the fresh air inside invest in a air exchange system.
Agree…and fresh air is good.
Gentlemen,
What is pictured appears to show a combustion air make up with an added damper.
Unless the furnace has a closed combustion chamber(2-pipe) the make up air is needed to provide a source of air back into the building envelope. Without this make up air the house would tend toward negative pressure relative to the outside and draw outside(unconditioned) air though any opening in the building envelope and also consume the oxygen with in the house. These have been a requirement since the mid seventies in this region as buildings began to be built with much tighter construction methods. These make up air runs are sometimes terminated in the cold air return to temper the air. The purpose of the added damper is unclear and perhaps someone else can clear that issue up.
.
Thanks, Michael. The tightness of the house being the determining factor. In new construction the requirement, up here, started in the late 80’s to early 90’s.