Replacing 50 year old Wall furnace with new one

liz k · 11-27-2009, 11:10 PM

So my old 50 year old Holly wall furnace is pumping out carbon monoxide so I thought it was time to replace it. I went and bought a Williams wall furnace at Home Depot thinking it would be a quick retrofit. We took out the old one and quickly realized that the venting needed to be replaced. It is really old big oval vent, with another smaller oval vent inside it. It also has a register venting to the room which I was told needs to come out. The biggest issue is the ceilings are vaulted so it's a bit difficult getting to the actual vent. My question is what is the best way to replace the old venting? I have basic tools, tin snips etc. I'm concerned about actually replacing the oval pipe going up through the roof with round, though. Am I in over my head here? I'm pretty handy around the house. I regularly do basic plumbing and electrical work. I'm an ME. I design and build small electro-mechanical machines for a living. This doesn't seem like it should be that hard to me.

Yoyizit · 11-28-2009, 12:18 PM

HVAC stuff is pretty hard; the equations are nonlinear and for some of it you just have to use look-up tables.

This library book
http://www.amazon.com/Mechanical-Eng.../dp/1888577681
has one or two chapters on HVAC stuff.

ASHRAE books are better but they are hard to get.

Are you sure the root cause was in the furnace?

liz k · 11-29-2009, 10:22 PM

I got it all figured out eventually. I was concerned I'd have to do major roof work or something, but it turned out the old flashing was still in good condition and it was the right size. I was able to push the old vent down and take it out through the wall opening. I then replaced the old vent with 6' of 4" oval vent and put an oval roof cap on it, and then I resealed the new vent to the old flashing. Good as new.

I'm just grateful to finally have a working furnace, with no carbon monoxide poisoning.

And yes, I'm sure the 50 year old wall furnace whose intended life time was only 20 years is the cause of the carbon monoxide. I proved that because the new one is not spewing it out at all.