Furnace and Central Air experts - I need advice

[Jeff C]

Last night during a long heat spell (Temps in the mid 90's with 85% humidity) my furnace fan went out. I made up a jumper to test the fan and it works.

So it seems it is a board that blew out somewhere. One of the circuit board boxes smells of burnt plastic......

the furnace and AC unit are 27 years old, and I think it is time to get a new furnace and A/C unit.

We have Carrier now, and we are looking towards the Lennox product line (Because, frankly that is the dealer that can get here quicker than the others).

I see the A/C units are at 18+ SEER

I have a two story house about 2,500 sq ft. Single zone system

What should I be looking for.....

I am about to make a rash decision, because the wife needs A/C in the house ASAFP.

I dont have proper time to research this, but even if I did I would not really know what to look for other than stainless steel heat exchangers and basic stuff like that.

the limited reading I did on this tells of furnace burners that gradually turn on as the heating demand raises, DC fan motors ar ethe standard now.....

HELP if you can!

 

[JSCC]

Most all high efficient 90% and above furnaces will have SS heat exchangers.
Lennox is a good brand.
Two stage furnaces are good. They basically run on low for low demand or high for high demand. Saving on your power bill.
Dont get caught up in "zones". Two story homes should have two furnaces. Different demands for each floor. Folks try to get around this by doing zones. Once it's all setup two systems would not be too far off in cost.
I also have a two story and installed a single furnace. In the eight years since, I have never done that again for any customer and never will.

Think in terms of cost vs return. If you run ac more than 6 months a year, the cost savings of going to a more efficient ac may be worth it. Likewise with the furnace. I install only 92% or better furnaces in all of the homes I build. We are in a colder climate. I leave the ac upgrade up to the homeowner. Some think it is worth it, most dont.

I hope that helps.

 

[Jeff C]

JSCC:

Thanks for replying.........

Another question for you. The way my furnace is hooked up, the return air duct size is ALOT less than the outflow, probably something like 1/3-1/2 smaller than the outflow.......

We have little air pressure up on the second story. The basement door has pressure on it (Sucking pressure - air is trying to keep the door closed).

Is this a result of the pressure differential between outflow and return air?

It seems like there is not enough return air, and the furnace fan motor is working very hard to get enough air to blow.........

What is the proper relationship between the main rreturn air duct and main supply duct in terms of sizing?

 

[JSCC]

Unfortunately I do not know the formula's for sizing duct. I leave that part up to my HVAC installer.
I do know that typically our cold air returns are of similar size to the supply side. We run them to central locations in the home. The theory is that the outside of the home is the coldest and hottest, so we locate the supply side there and pull that conditioned air toward the middle of the home.
It is not uncommon to have some pressure from one side of a door. But it is not desired.
To combat the same issues you are having with my own home, in the summer I will close off a handful of lower level vents and open more upstairs, and vice versus in the winter. I never close off return air though. I feed it all the air it can get. So if you are not sized adequately for return air this may not work. If you can get another return air run upstairs or to the side of the home that is feeling inadequate, it may help.