No actual Duct, Just CInder Block Pathways

Formally known as a hypocaust, which dates back to Roman heating systems.

When they noticed it they should have suggested something to improve it.

Not being able to see we can't give accurate information. If possible, putting in an insulated duct would be best. An alternative is spray foam insulation. Keep in mind, anything you add can change air flow but depending on sie, it may or may not matter.

It might be easier to buy a box of insulated flex duct and bypass the block completely. Just be sure to run it as straight as possible. I really like to run it on top of a running board. Sags in the duct reduce air flow.

On Fri, 18 Jun 2021 15:36:33 +0000, Tanner posted for all of us to digest...

registers 42 degrees from the coils, so it's getting cold enough, however, when the air actually comes out of the vent it's up to 64! I believe we are losing a ton of efficiency here due to to there being no duct work and the cinderblock "ducts," not being sealed. Is there any simple fix or something that can essentially spray coat the entire duct area underneath my house to seal it and hopefully run my A/C more efficiently?

You are getting a 22 deg drop. Did you measure it when the house was hot or cool. What was the room temp when you measured it?

I would duct if possible.

If the concrete nonduct (I would call it a plenum) is very large your airflow is probably very slow.

Another possibility is that the concrete has a large capacity to hold heat, and that eventually you will cool that thermal mass down enough that the air temperature will start to drop. Of course that process would reverse in the summer.

That's what I was wondering too. If the house is 80F and that's the incoming air temp,