Jump to content


Bill Kibbel

Recommended Posts

Click to Enlarge

32.24 KB

This furnace and A/C replacement resulted in the system being located directly under a steel beam. The evap. coil is very tall. I suspect the previous system was shorter, allowing for a reasonable oblique duct connection.

I need some ammo to counter the response from the installer regarding this offset..

Link to comment
Share on other sites

I take it that we're looking at the front of the evap with the steel beam over it on the left hand side? Then it looks like the supply plenum hugs the beam yes?

Now there is an offset from the outlet of the evap to the supply plenum. It also looks like they put sheet metal over the bottom part of the supply plenum where it use to line up but is now capped off. Was there a reason they couldn't line everything up?

If what I've said is correct about the installation then they have dramatically changed the air flow pattern around the evap. The end result will be air stratification and most likely freezing the part of the coil that isn't seeing correct air flow. Low superheat because of bad airflow & liquid coming back is a possibility. You'd need gauges and a few strap on t/stats the see how the system is functioning.

Last, but not least, is how much air flow has been cut down? If you have a duct-o-lator, you can get the cfm for the original size of the plenum then get the new dimensions to see exactly how many cfm they're now losing.

It's incorrect no matter how you slice it.

edit: I doubt a manufactures warranty would hold up if they saw how it was installed. When systems are installed incorrectly, as this one is, they are a nightmare until ripped out and installed correctly.

Link to comment
Share on other sites

I would liken that install to a hole hacked into a cast iron or PVC vent stack for the AC condensate pipe. A proper fitting is needed.

That offset is without a proper 'fitting'. I'd counter the installer by asking him to show the documentation that gives the friction loss of that exact arrangement, right down to each and every measurement. Most likely, that documentation doesn't exist because it's the installer's own tribal invention.


Link to comment
Share on other sites

Air is a lot like a fluid in this case.

Trying to force 300 CFM through an opening that will only accept 50CFM is like trying to push water from a 2-inch pipe through the ice supply line for a fridge - volume coming out of that little pipe will be greatly reduced regardless of the pressure behind it and overall performance is gonna suffer.

That system will probably take four or five times longer than it used to take to heat/cool that house.



Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...