ceclmc

I installed an A-Coil in my old American standard furnace. The A/C worked great for the summer but, I was wondering if I could reduce the gas pressure to reduce the main plenum temperate on my furnace in order to melt the plastic tray that the A-Coil sets in? What is the max temperature that the A-Coil can take? I also sped up my blower by replacing the pulley for the A/C. I was told that slowing it back down for heat was the thing to do. Sorry for such a long post. But I was trying to cover all bases.

Thank you, Chuck

ceclmc

Maybe I'm not asking the right Question? What is the upper limit in degrees that an A-Coil can safely handle?

Thanks, Chuck

ohmoheknows

I would have to look that one up but in my 20+ years as a tech. i've never seen a furnace temp. so hot that it burns the plastic on an evap. coil. There should have high temperature limits inside the furnace that will protect the coils

paul52446m

Hi Paul here. Most coils are made to take the temps
of a gas furnace. Most furnaces are designed to have about a 70 degree temperature rise across the heat exchanger. So if the return temp is 70 degrees then the out going temp should be about 140 degrees. If you check this out it will give you a idea of whether you are turning your blower at the right speed. You furnace is designed by stack size and baffles to be efficient
at a proper gas pressure. So if you drop that pressure you will lose a lot of
efficiency, and it will cost you a lot more to heat your home Later Paul

ceclmc

Thank you, for your responses.

I have about 70 degrees rise. but i had to reduce gas pressure significantly. Also changed pulley on the blower to hit motor FLA. so I guess I'll Have to see what it does this winter.

Thanks, Chuck

paul52446m

If you do not have that gas pressure set right to match the input and out put of the furnace then you could be under firing it which i talked about in my last
message, and you will lose eff. and cost you more to heat your home.
Do you know what the gas pressure in on the header or out going side of the gas valve?

ceclmc

Paul, I don't know the gas pressure or how or where to check it. What type, or range of gauge to use. I have uploaded some pictures that might be helpful.

Thanks, Chuck

paul52446m

In the first pic. your two burners are coming out of the 3/4" pipe header.
Between the two burners is a little 1/8" pipe plug. We take that plug out and
hook up our U tube pressure tester at the point. The pressure at that point with the burners going should be 3and 1/2 inches of water column.
You would need a heating tech to check this because you would not have the
tester. You are testing less then 1/7 of a lb. of pressure.
If you have the pressure set way to low then your efficiency will drop way
down and it will cost you more to heat your home and you might not get enough heat out of it to heat your home. later paul

handypilot

You can test this yourself very easily with a home built manometer. I did it myself using these instructions: Manometer

Simple, easy, cheap...that's how we're suppose to roll!

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paul52446m

Yes you are right , you can build your own manometer tester. This is the most accurate way of testing low pressures. If your water is not so good then you should use distiled water. Later Paul