Cold Air Return. Do I Need It?

larryfoster · Post by **larryfoster** » Fri. Nov. 21, 2014 6:04 pm

Why, were you on the team that sent that probe to the comet?

No but they made several movies about me with Jeff Daniels and Jim Carrey.

Would a single centralized drop work or do me any good?

Post by **Lightning** » Fri. Nov. 21, 2014 6:39 pm

larryfoster wrote:Would a single centralized drop work or do me any good?

Yes, this is exactly what I have. Its a 24x8 inch rectangular trunk that descends from a central point on my first floor to the basement. It's not best case scenario but it is 100% better than nothing.

larryfoster · Post by **larryfoster** » Fri. Nov. 21, 2014 6:55 pm

I'm stuck with doing something like this with the layout of the basement as well as the other ductwork to work around.
I was looking at round flex duct.
Also, I don't have a lot of room between the back of the filter box and my chimney

Post by **Lightning** » Fri. Nov. 21, 2014 7:27 pm

Flex duct isn't really designed to handle negative pressure.
I suppose it would work but may choke the convection system a little.
Can you run tin round duct for your cold air return?
Where is that HVAC member? His advice here is needed..

larryfoster · Post by **larryfoster** » Fri. Nov. 21, 2014 7:30 pm

I could run round duct.
How big might I need or how small can I get away with?

Post by **Lightning** » Fri. Nov. 21, 2014 7:39 pm

larryfoster wrote:I could run round duct.
How big might I need or how small can I get away with?

Can you run two 8 inch round cold air returns to match the two that come off the furnace for warm air? I would think that this would be the bear minimum.

michaelanthony · Post by **michaelanthony** » Fri. Nov. 21, 2014 7:44 pm

Lightning wrote:
larryfoster wrote:I could run round duct.
How big might I need or how small can I get away with?
Can you run two 8 inch round cold air returns to match the two that come off the furnace for warm air? I would think that this would be the bear minimum.

you could save some cash and by the size sonotube you need...and they come in some big sizes!

larryfoster · Post by **larryfoster** » Fri. Nov. 21, 2014 8:02 pm

I'd have to measure.
The big challenge is how much room I have between the filter box and the brick chimney.

I'm guessing 8" would be pushing it but I might.

Also, the weather is mild on Sunday.
Might be a good time to let the fire burn out and check my chimney to see if I can get more heat out of the furnace or improve my draft

larryfoster · Post by **larryfoster** » Sun. Nov. 23, 2014 11:28 am

You all have been very patient and generous with me and I appreciate it.
Thank you.

Here's my plan for today.
Because it's a little nicer I let the stove burn out.

I'm thinking that I need to see if I can get more heat out of the furnace and I'm starting with the draw.

I'm going to clean it out good, disassemble the pipe from the furnace to the chimney and inspect it and, hopefully, the chimney for any obstructions.
It is brand new but installed several years ago and used for the first time this month.
The short horizontal run from the furnace to the chimney only has a very slight elevation to the chimney.
Not much.
Is that enough?

Here's my setup now.
I come out of the furnace with an ell which goes into a tee which holds my baro damper.
(I don't know if it's adjusted right or not.)
Another ell then my horizontal run, maybe 24" into the chimney.
It does draw, maybe not enough?

See if I can put a return where I'd like to

larryfoster · Post by **larryfoster** » Sun. Nov. 23, 2014 12:11 pm

Preliminary results are not good.
My grate is full of clinkers. Big unburned lumps.
But the worst was the flue was packed full of soot.
There couldn't have been any draw.
I reached up in to the chimney as far as I could and the stainless liner had a thin layer of soot.

Is this because I'm not hot enough?
At the very beginning, I burned exclusively wood.
It wasn't dry enough so I stopped and got coal.
If I clean this out will it come back now that I'm not using the wet wood?

michaelanthony · Post by **michaelanthony** » Sun. Nov. 23, 2014 12:17 pm

Berlin wrote:If your basement is very leaky this is part of the problem. Creating additional negative pressure in the basement by producing a lot of hot air down there increases infiltration which substantially reduces system efficiency. I've seen homes with basement returns require 20-30,000 BTU's more than they should need to heat the house, not to mention it's not terribly safe. Not having a return from the living space and leaving the basement door open also reduces your draft.

High coking coal that crusts over as well as poor draft or air escaping around the fuel bed cause low heat output as well. You should also have an 8" dia. stack and connecting pipe with hand-firing bit coal, the size on the hot blast collar is irrellevant. If your SS liner is 6" it can fill with soot quickly and dramatically reduce draft as well as peak cfm flow also allowing smoke spillage from the loading door while reloading.

You can and should tie your return air to your existing system, but, it should be done in this way: Cut into the return drop and slide a piece of sheet metal in OR use your existing filter slot and cut a piece of sheet steel to fit nicely and slide it in in place of your filter. You could also do this in the supply plenum if you choose (if you have a circuit board in the blower cabinet). Then connect your blowers to the return air trunk or drop before the blocking plate, make sure you have adequate flow - you probably want at least 16x8 duct on your blower return. Make sure your propane furnace is shut off when you have the plate in place. cut another slot for a baffel in the return drop for your hotblast that you can insert when using the propane furnace.

Check this out, Berlin has been doing this for a while and makes some valid points.

larryfoster · Post by **larryfoster** » Sun. Nov. 23, 2014 12:36 pm

Thanks, Michael for your speedy response.

High coking coal that crusts over as well as poor draft or air escaping around the fuel bed cause low heat output as well. You should also have an 8" dia. stack and connecting pipe with hand-firing bit coal, the size on the hot blast collar is irrellevant. If your SS liner is 6" it can fill with soot quickly and dramatically reduce draft as well as peak cfm flow also allowing smoke spillage from the loading door while reloading.

I only have a 6" stack.
If there is any other alternative to replacing it, I'm open to suggestions.
That's a $700 bill if I do it myself and a lot more for someone else.

Crap!

michaelanthony · Post by **michaelanthony** » Sun. Nov. 23, 2014 12:44 pm

Ok how about replacing the ell's with Tee's with covers on the ends for cleaning, you may need to vacuum soot and fly ash every few days.

larryfoster · Post by **larryfoster** » Sun. Nov. 23, 2014 12:51 pm

I could do that relatively cost effectively.
Would I have to let the fire burn out to do this?

michaelanthony · Post by **michaelanthony** » Sun. Nov. 23, 2014 12:54 pm

larryfoster wrote:I could do that relatively cost effectively.
Would I have to let the fire burn out to do this?

Absolutely, we have a heat wave coming how about you?