Considering new furnace

[catmanacman]

the savings is going to come from the varible speed motor as ecm motors consume less energy if the duct work is sized properly.no matter the brand they all use the same motor. you might need a oversized furnace to get the full seer rating .

[caincompany]

Sure, the 95% furnaces are nice, a lot more up front cost but it does save you money. Of course in Atlanta the savings wouldnt be like it would in northern Michigan. Either way you can use what ever brand you want, as long as the airflow from the furnace is set up right. You would have to do that with trane or lennox or amana.

[545GAlady]

Thanks very much! We are leaning towards the Amana, but we might have one more company come out to give us an estimate. I've always wondered what brand ECM motors are used on these three furnace brands. I know the brand of the motor won't matter much, but I'm just curious. Do any of you know?

[545GAlady]

One more question, Are Goodman/Amana furnaces loud? I've heard they are but I'm not so sure. We really want a quiet furnace. Of course condensing furnaces will still be quieter than 80% efficient furnaces.

[caincompany]

Quiet but not like lennox

[545GAlady]

Ok thanks! We are short on return on the whole system, with only 7 8 inch returns. There's a total of three ducts coming off the return box which two of them are 10 inch. The other one is either 10 or 12 inch (most likely 10). The contractor mentioned that another return will have to be added, but it can't be added through the wall unless its a new construction, according to code. A new return will have to be installed in the floor. The current returns are located low on the sidewall. A 3.5 ton system needs 1400 cfm,and our current furnace has a 4 ton blower which can go up to 1600 cfm. I'm surprised he didn't exactly say what size return should be added. What do you think? Unfortunately, I don't think we're able to downsize on the furnace since the heat pump is 3.5 ton, which requires 1400 cfm. Is there is a brand that has a 70,000 BTU furnace with a 4 ton blower? Our current furnace sometimes short cycles. It heats up the floor in short period of time.

[caincompany]

You can use the sl280v, it has adjustable airflow and two stage heat.

Ok thanks! We are short on return on the whole system, with only 7 8 inch returns. There's a total of three ducts coming off the return box which two of them are 10 inch. The other one is either 10 or 12 inch (most likely 10). The contractor mentioned that another return will have to be added, but it can't be added through the wall unless its a new construction, according to code. A new return will have to be installed in the floor. The current returns are located low on the sidewall. A 3.5 ton system needs 1400 cfm,and our current furnace has a 4 ton blower which can go up to 1600 cfm. I'm surprised he didn't exactly say what size return should be added. What do you think? Unfortunately, I don't think we're able to downsize on the furnace since the heat pump is 3.5 ton, which requires 1400 cfm. Is there is a brand that has a 70,000 BTU furnace with a 4 ton blower? Our current furnace sometimes short cycles. It heats up the floor in short period of time.

[545GAlady]

You can use the sl280v, it has adjustable airflow and two stage heat.

Thanks! We will look into that. One final question, what type of floor registers do you recommend?

[545GAlady]

I'm still concerned on the amount of return air we have currently. I need to make a correction, one of the ducts coming off the return box is a 12 inch, which feeds three 8 inch returns. The other two ducts coming off the box are 10 inch, with each feeding two 8 inch returns. I really doubt it, but does this sound enough?

[RyanHughes]

I'm still concerned on the amount of return air we have currently. I need to make a correction, one of the ducts coming off the return box is a 12 inch, which feeds three 8 inch returns. The other two ducts coming off the box are 10 inch, with each feeding two 8 inch returns. I really doubt it, but does this sound enough?

Sounds like bare minimum, rule-of-thumb sizing for me. May be fine under ideal circumstances with hard pipe (not poorly done flex). Having seen your ductwork, it is certainly not enough capacity for 3.5 tons at the time being. If adding more returns isn't necessary (seven 8" done right -- meaning pulled tight and run straight if flex if involved -- can provide ~200 cfm each), I would at minimum replace sections that come right off the plenum with solid duct. Improve the transitions to these round ducts -- don't just tap them off the top and bottom of the unit again. A new furnace, set up right, with a variable speed blower is going to help move the air better throughout your home, no doubt about it in my opinion. But your ductwork needs a lot of improvement as you've heard before and understand. I would try to minimize the flex involved. Good luck.

[545GAlady]

Thanks for the info. It is possible for another return to be added, but the contractor never mentioned what actual size is needed. He mentioned about installing a 90* elbow at the return box for the 12 inch duct since in comes off the side and currently has no metal elbow in place. Does this sound like a bright idea?

[RyanHughes]

Thanks for the info. It is possible for another return to be added, but the contractor never mentioned what actual size is needed. He mentioned about installing a 90* elbow at the return box for the 12 inch duct since in comes off the side and currently has no metal elbow in place. Does this sound like a bright idea?

The 90 deg elbows will help (to all of the returns coming off the box, the two 10" and one 12") compared to the sharp flex bends. Can you extend solid duct any further to where this flex enters the mechanical closet? All of the return runs from the unit to the grilles are flex, correct?

[545GAlady]

The 90 deg elbows will help (to all of the returns coming off the box, the two 10" and one 12") compared to the sharp flex bends. Can you extend solid duct any further to where this flex enters the mechanical closet? All of the return runs from the unit to the grilles are flex, correct?

The other two ducts are coming off the top of the return box. It might be possible for solid duct to be extended. Yes, all of the return ducts are flex all the way.