Hey there all, new here and I am looking for some advice.
I am getting ready to install a Goodman GMVC 95% 2 stage, variable furnace and I am revising my ducting in the house, it was a good design but I want to make sure that the furnace is going to run to it's best potential.
Some specifics on the house 1200 SQ FT. Cape cod style house, built in 1938, located in SW Michigan. We had new windows installed in the house, which is a drastic upgrade over the single pain units
I purchased all the software and tools and what not and did a ton of research on equipment sizing and all of that. That being said with everything calculated out I bought a 70K, well actually 69K input furnace and 2 ton 16 SEER AC.
Currently the 30 year old furnace heat exchanger has a small hole in it and the gas meter is humming when it is running, it is currently 105K input 80% eff. with no AC. So I need to get all this done in a rather quick fashion.
Now for the supply ducting what I have calculated out is that the current supply from the furnace is 8X16, to 8X14 to 8X12, isn't adequate and I need to up size the supply ducting to 8X20, to 8X16 to 8X14 Forgot to mention that the furnace is on one side of the basement. This is one portion that I am modifying, but I am also going to convert the supply registers in the bedrooms to return air ducts and move the supply's to the outside wall as they are all on the inside wall except for the living room. I am also going to cap off the big return in the kitchen, add a supply register in it's place, run another supply to the upstairs as there is only one feed currently and it needs at least two more as well as return air up there.
This brings me to the question on the return air duct, currently the duct right above the plenum down to the furnace is 8X24 then as it runs down it drop down to 8X12 about 4 feet after the furnace. Question is being that I am converting the supply vents in the lower bedrooms to returns, then I should upsize this return duct as well, correct. It should note that the 8X12 duct also has the return air from the kitchen, which I really think is grossly undersized. as there is only two returns in the house currently, one directly above the furnace near the front door and one in the kitchen which is on the other end of the house.
Any advice would be great, thanks for the help. Also attached is the PDF of the drawing that I made of the way the system is currently, yes I am an engineer
Anyway, thanks again in advance.