Replacement furnace has no blend air & roof jacks

[ronmow]

I'm getting ready to install a metal roof. The original furnace was replace about 10-15 years ago with a Coleman Mdl. 7995C856. The old roof jack was maintained (Coleman 7900-8181) and it has a big square box that the vents come through that are not going to be conducive to seal around the new roofing material. I think I would like to replace the roof jack with a newer model that has a round flashing. Are alHi,
l the pipe diameters one the old model compatible with your newer roof jacks? If so, I understand all I need to do is get the length from the top of the furnace to the outside roof. I will also add an exterior extension.

Now the main question. The first furnace must have had a blend air system as there is an additional roof jack (again with the square box design). There is flexibles vent tube from there to the top of the furnace. However, whoever installed the replacement furnace did not install a blend air system. The flex pipe is just positioned over the knockout on the top of the furnace. There are some slots around the knockout that would provide a tiny amount of air to enter. However, the flex vent wasn't even taped down so I suspect that room air is all that is getting in.

Is the blend air necessary? We've been operating the furnace all these years without it. If it's not necessary, I'll just remove the blend air roof jack when installing the new roof.

[Robert]

Hi Ron,

Yes, the newer roof-jacks should fit the furnace fine.

The blend air systems are two types, standard with just a fresh air tube from roof that blower pulls in.

The other is a deluxe with same fresh air and also a roof motor to ventilate the attic cavity of humidity and moisture.

The latter is the most important of the two issues they are used for.

Below are the chimney and roof-jack page where you can see and order through PayPal needed roof-jack and extension and hydroment sealant.

Also, the blend air systems troubleshooting article for good info on both systems and how to test them.


Then, the store page for blend air parts that can be ordered same as roof-jacks

http://www.mobilehomerepair.com/ColemanChimneys.html


http://www.mobilehomerepair.com/ArticleBlendAir.html


http://www.mobilehomerepair.com/ColemanBlendAir.html



Hope these help.


Take care and best wishes,
Robert