Considering new furnace

[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.

[dan sw fl]

Thanks for the input. I'm still having a lot of trouble deciding on what to go with. I would like to get the extra seer, but the cost is higher for the Trane. In fact, the Trane and Lennox price is the same. The Amana is cheaper. I'm still wondering about 95% efficient furnaces because we have some neighbors who have them and enjoy them. Do you think condensing furnaces are worth it down here?

The problem is, I don't want to mismatch brands due to the fact you won't receive the full efficiency of the system.

You're Best Bet will likely be to save your money for another day.
You might be able to save $40 a year with a new furnace.

What is your electric rate$?

[545GAlady]

You're Best Bet will likely be to save your money for another day.
You might be able to save $40 a year with a new furnace.

What is your electric rate$?

That does not sound much at all!

Our current electric rates are 9 cents/kw per hour.

What's your opinion on modulating furnaces? Are they worth it this far south?