I'm so happy to have found this forum! We have an 1800 sf single story house in North Texas (20 mi. North of Dallas. Our Lennox furnace is 18 years old and needs a new gas valve. We have decided to replace it and have received 3 bids. All bids are from reputable HVAC pros that have been in business 10+ years in the area. We have a 4 ton 10 SEER Trane AC unit that was new in 2000. The bids include a new evaporator coil as the existing one is rusted through the bottom of the pan. We also need the return duct and a few other ducts replaced. We got bids on a single stage 80 AFUE and a dual stage 80AFUE furnace - one American Standard Freedom 80 Two Stage or single stage, one a Trane TXCO49 two stage or single stage, and one Payne 4 Ton Single Stage. Two contractors said a two stage furnace would be more comfortable, one said the house was small enough that it wouldn't matter. I'm confused about which is the most appropriate furnace - the single or dual stage. All recommended a 4 ton unit. No one said anything about BTUs. Please help! Thanks, Diane
Anyone have opinions about 2 stage vs. single stage furnace as described above? Thanks, Diane
First thing that needs done is a load calculation to size equipment to your conditions.
Second item that needs to be addressed is the ductwork, to insure the new equipment operates with-in the manufacture's specifications.
The two-stage unit will fire on low, and reserve the high fire for more demanding conditions. This will allow your home to gradually rise slowly towards the set point. Which will aid in your comfort. It will also aid in filtering the air as well as providing a more even temperature throughout your home.
Two-stage equipment is for COMFORT.
Make sure you get a two-stage stat installed with a two-stage furnace. Otherwise you are not gaining the full advantage of the equipment you purchased.
Not that I like complicating things for you, but was your airflow assessed? Many (most in my opinion) 4 ton furnaces don't deliver 4 tons of air. A furnace's tonnage rating is only a nominal rating based on having a nearly ideal duct system installed. Will the proposed duct upgrades allow the 4 ton furnace to actually deliver 4 tons? I'm skeptical. But the only way to know is if they measure. Are they going to measure? Do they even own the expensive tools need to measure airflow?
A 5 ton furnace will often cost very little more than a 4 ton furnace. That extra bit of blower power will allow you to truly deliver 4 tons worth of air if it turns out your ducts are a little restrictive. And if it turns out to be too much, you can just turn the fan speed down. But if it turns out that your ducts are indeed restrictive (even after the upgrades) then you won't have any reserve power with a 4 ton furnace.
It's just a thought. I don't have real answers because I'm not there. If one of your salespeople really assessed the system then they could answer this question of airflow.
Go with the 2 stage furnace and 2 stage stat it's a no brainer
Que why get 3 prices from 3 contractors spec-ing 3 different manufactures? there's part of your confusion.
Why not 3 contractors spec-ing the same manufacture and model.
But remember it's the expertise not the brand or price that determines a proper installation
And as stated get all the perticulars looked at, duct, heat loss and gain calcs etc.
A note on the 1 stage vs 2 stage debate.
One of the issues we have here in the DFW area with heating equipment is that gas furnace heating capacity is almost always oversized. This is because we have to select a furnace that has a blower with the capacity we need for cooling.
Unfortunatly it is very common that the minimum heating capacity available in a furnace that has the blower we need is still quite a bit more heat than we need, even if the temperature outside is at our 20ºF design conditions.
This oversizing is agravated by the fact that we spend most of the winter with overnight lows in the 40's and 50's, with only a few weeks in the 30's and brief dips into the 20's.
With a single stage furnace, that is likely oversized anyway, the system short cycles most of the time. This not only leads to uncomforterable hot and cold spots, but reduces the actual efficiency of the furnace, because it doesn't run long enough for the heat exchanger to reach a steady efficient operating temperature. It also shortens the life of the equipment.
With 2 stage heat you get longer run times, so you get more even comforterable heating, and the furnace operates much more efficiently.
When it does get really cold out, if you also have a 2 stage thermostat, the furnace will run nearly constantly in 1st stage, wich is very comforterable, and cycle 2nd stage on as needed to maintain the temperature.
I would not even considder a single stage furnace. You should look into getting one that also has a varriable speed blower. It takes comfort to the next level, especially in the cooling mode, and will save a good bit of electricity over the years.
Thanks for the replies. Mark Beiser's reply is almost exactly what the contractor told me - said the 4 ton unit was necessary more for the AC than the furnace, and recommended re-doing some of the ductwork to increase comfort. Replacing some of the ductwork was nesessary anyway as it is the gray flex stuff and the outer layer has deteriorated. We had noticed this previously. This particular bid was between the other two pricewise but much more complete on all other aspects. As for the different brands, when I called places to get estimates my first consideration was whether or not they were a local (to my town) business, how long they had been established, and what our community message boards said about them in terms of service. Based on those factors, I called three companies for bids. I didn't realize there were so many brands out there, so I guess I should have compared apples to apples. Thanks for the informative replies. Diane
diane, somewhat off the subject, but can you tell me how your community bulletin boards work, and how you access them? Thanks. Is this something that you would normally go to in order to check out a service or company?
Everyone has a purpose in life..........even if it's to be a bad example.
Seek first to understand, before seeking to be understood.
community message boards
We have a community message forum very much like this one at http://www.allenonline.com. Several communities around the area have them. The owner of the site accepts advertisements and provides basic webpage services or links directly to the site. Most of the forum posters are careful not to discuss businesses that don't advertise there as we know the website is the owner's family business. However, there is a private message feature that people utilize if they need to discuss topics not suitable for the forum. I have come to rely on the businesses that advertise there - they are very attuned to the fact that they are a local entity and not a big box operation.