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NJ user 02-04-2009 10:42 AM

Replacement furnace, add AC coil now??
We are replacing a 31 year old gas, forced hot air furnace in a house we moved into recently. We are upgrading from a 80,000 BTU to an approx 120,000 BTU Carrier system. We also have a fairly old central air system which does not run through the furnace. When we asked the HVAC service team if we should consider running the AC through the furnace, they advised that it would cost an additional $495 to add the coil now to the furnace and would be easier than doing it in the future. We are in NJ and not huge AC users, but do like to cool our house once in a while. We are trying to decide if we should bother with the additional expense at this time. Being newbies to this combination of a heating and cooling system, we thought we would put the question out to this group. Any feedback would be appreciated.
Thanks in advance!

beenthere 02-04-2009 11:47 AM

First. Why are you increasing the size of yur furnace. Do you just want to pay the gas company more money.

Or are you adding a BIG addition, with teh size increase you posted.

The A/C coil is part of teh A/C, not furnace. By having the coi installednow. You limit yourself as to tehchoise and efficiency of A/C you can hae later, without buying another coil.

Have a load calc done to know what size furnace you need.

After all, that bigger furnace will most likely need much bigger duct work to work properly.

NJ user 02-04-2009 12:31 PM

Part of the reason that we are increasing the size of the furnace is that the existing furnace cannot get enough flow to the outer reaches of our existing duct work. So we currently have uneven heating in our house (although part of that is just the way it is in split level homes). According to the furnace guy our current furnace btu level is not enough to heat a house our size, his impression not a measurement. There was an addition done after the original furnace was installed which used to be heated by wood stove and now is not heated at all (got to love the sun coming through the windows in the winter). Since our furnace is so old, we think we are paying far to much in gas now and expect a newer more efficient, up to code furnace to help tremendously.

Our house has a home warranty covering part of the cost of the funace, so we have to pay $2,500 while the warranty covers the other $1,500. We have young children, so are reluctant to let the old furnace linger.

The AC coil was a question that we presented to the furnace guy. My partner was the one who asked about it and I am the one trying to research and make a decision about it before Friday. I want to make an informed decision about adding a coil now, but I think a decision to add now would just be jumping the gun.

Thanks for your feedback. Any other thoughts?

beenthere 02-04-2009 02:27 PM

Unfortunately. A lot of contractors will tell customers that upsizing the furnace will get more heat to the rooms that aren't heating up evenly.

All too often, what happens is. The rooms that always heated well, just warm up faster. So the furnace shuts down sooner. And those rooms that were cold with the old furnace, are still cold with the new larger furnace.

Your duct system its self is what the problem is. Its undersized, or it isn't balanced.
Which is why your not getting enough air to those poorly heating rooms.

The new larger furnace, may use more gas then the old one did. Since it will need to move more air then the old one. But the duct will be too small.
So it will over heat and shut down on its high temp limit, and short cycle for you.

If your feeling brave. You can do your own load calc.

That is a software, you pay a fee for, that you can use for your house for X number of days.

Then you may be able to show your contractor that you need to increase the size of your duct work, not the furnace.
Although some won't believe it, since that would mean they were wrong. And that they don't get to sell you the larger more expensive furnace.

You'll also know what size A/C you need. And if your current one is oversized.

Instead of increasing furnace size.

Sealing/caulking around your windows and doors, along with sealing all receps and switches on your outside walls will save you more money then a just a new furnace will. It will save you money both winter and summer.

drtbk4ever 02-04-2009 05:26 PM

I am a real noob, but have to agree with BeenThere.

From my personal experience arbitrarily increasing the BTU size of the furnace sounds like an "upsell". When I upgraded my old furnace to a high efficiency, I believe we actually went down on the BTU slightly.

NJ user 02-05-2009 07:45 AM

Thanks for the time you took in responding to my questions. I misquoted my old furnace and we are planned to go from a 95K btu to around 120K right now. We did more research last night and are calling the furnace guy with more questions. We are looking to make sure what they are proposing is more efficient as expected.

We also wonder about the size of the ducting, since the house is over 50 years old an the ducting is original. I appreciate the information on the load calc and think we will give it a try.

We are definitely holding off on anything to do with the AC for now and appreciate all of your insights which helped us make this decision. Plenty of time for that later.

Will update when we finally finalize our thoughts and for those with any other feedback, please feel free.

Thanks again!

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