1 or 2 Stage Furnace

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Old 12-07-15, 07:29 AM
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1 or 2 Stage Furnace

Unfortunately, my 1992 Bryant furnace needs to be replaced. My HVAC contact is recommending a Goodman 2 stage unit. The cost of the 2 stage is only $300 more than the single stage, but how much savings can I really expect out of the 2 stage unit? Is it worth the extra cost if I plan on selling the house within 5 yrs?
 
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Old 12-07-15, 03:58 PM
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WHY did your repairman suggest that the furnace be replaced? The best reason is that you have heat exchangers that have holes and cracks which you were able to see when shown by the repairman.

Unfortunately, a lot of furnaces are changed out when its not necessary to do so.


Whether you have a one or two stage furnace isn't especially important. First I'd be sure that replacing the furnace is what you really want to do.
 
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Old 12-08-15, 05:17 AM
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The heat box is cracked and the pressure switch is failing. The overall condition of the internals is poor. The guy doing the work is a trusted friend, so I believe it when I'm told the furnace should be replaced.
 
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Old 12-08-15, 07:55 AM
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A 20+ furnace with a cracked heat exchanger needs to be replaced.
 
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Old 12-08-15, 09:06 AM
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Your question was a single or two stage unit. If my understanding is correct, you want a 2 stage. And by 2 stage (I believe there is another term) I mean a unit that will shut off the heat but the fan will still blow warm air for up to a half minute to expel the heated air from the plenum and heat ducts into the rooms. Otherwise that heat is pretty much wasted.
 
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Old 12-08-15, 09:19 AM
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A single stage furnace burns at one rate while a two stage furnace has high and low burn rates.

The two stage is a selling feature when you sell the house and will save you money.
Is it enough of a savings to recoup in five years..... doubtful.
 
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Old 12-08-15, 09:34 AM
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Thanks Pete, wasn't sure about the two burn rates. So what is the extended fan blowing feature called? I know it was a selling point when I bought my new furnace several years ago.
 
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Old 12-08-15, 09:57 AM
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Furnaces either have a fan thermostat or a timer function on the control board to control the blower. With the furnaces that have the timed function..... it's usually user changeable and can be set from 60-120+ seconds of run time after the burner shuts off.
 
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Old 12-08-15, 12:33 PM
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If you get a goodman 2-stage be sure it's a gmvc and not a gmh.

$300 more sounds like a gmh.

Gmh 90%+ looks to be discontinued. If you're in a heating dominant climate, don't get anything under 90%.

Goodman is a low end brand, and as such, they really cut corners on some of their furnaces and a/c units. opened one once - metal is thin, edges are sharp, access panels don't fit very well. Goodman apparently used to be total junk.

The GMH while being 2-stage, has a single speed ventor motor which moves too much air for combustion/exhaust on low heat, which throws off the fuel-air ratio and wastes gas. The 80% afue gmh could be in the low to mid 70s on low fire. It's not even rated for efficiency on low fire, otherwise it wouldn't even meet the minimum required by the government.

The staging on these furnaces is strictly time based, so it will only run on low for the first 1-12 minutes of each cycle and switch to high, whether the house needs it or not.

The better ones are controlled by a two-stage thermostat and only run on high if low won't keep up. Properly sized two-stage won't run on high unless you bump the stat up or it's bitterly cold.

GMVC96/8 is what i would go with for two-stage. It's is a fully featured product with a energy efficient variable speed blower and the price will reflect that. There's a GME8/9 model too which is better than the gmh, but heating fan speeds are not adjustable (different controls, different programming on the blower motor), meaning you may run into trouble if your ducts are undersized.

The blower motor in the gmv models automatically adjusts itself to deliver the correct amount of air even as filters get dirty, also uses 30-50% less electrcity, 66% less in continuous fan mode.
 
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Old 12-08-15, 01:07 PM
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For only $300 more I would definitely opt for the two-stage furnace. There isn't all that much difference in efficiency between the two firing rates but you WILL have greater comfort with the two-stage. Also, if you have a smaller house sometimes a two-stage is the only way to get a furnace that is properly sized for the house.

I have a two-stage furnace and even when the outside temperatures are in the thirties the first stage cycles on and off to maintain the inside temperature within about a half a degree of setpoint. It does have longer burn cycles on low but that helps to keep the furnace firing at top efficiency and also evens out the temperature throughout the house. With a larger furnace you will often get short firing cycles and a "freeze or fry" syndrome with varying temperatures.

As a bonus, if you use a deep temperature setback the second stage can come on to warm the house much faster than a single stage furnace while still firing at a high efficiency.


Muggle, thank you for that information on the Goodman furnaces. I have a Lennox and it DOES have the two-speed induced draft blower. I also have a two-stage thermostat.
 
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Old 12-08-15, 05:22 PM
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All the furnaces are getting cheaper and cheaper. Most new sealed units now don't have a burner box, the cold air just flows into the cabinet and the access panel makes the seal.

All the R&d seems to be in advanced controls, communicating/wifi this and that. The advanced controls are probably too complex for most residential techs and don't get used, are totally proprietary - super expensive circuit boards, $500 stats. Wish they would focus on just building a decent quality unit for a change.

Getting difficult from what i've seen online to get an affordable* non-crippled two stage furnace with a psc blower motor, two speed inducer. They're putting x13 motors in them to get the energy star certification now. The ecm is great until the repair costs come, doesn't pay for itself unless the fan is run continuously or it's used to get a high seer rating from a high end a/c, and seer above 14-15 is kind of bogus anyhow.

*For the op, i think york makes one if you don't want the ecm motor ->TM9T. the goodman gmh i would stay far away from.
 
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Old 12-08-15, 05:52 PM
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Wish they would focus on just building a decent quality unit for a change.
I'll agree with you there.
 
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Old 12-09-15, 06:03 AM
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If you are planning on selling in a few years then you are most likely not to get your money back upgrading to a two stage unit. What you would get with a two stage is a quieter system with smaller temperature swings.

The bigger choice is efficiency. A standard furnace is 80% which exhausts up a chimney. A newer high efficiency style is 90% or higher normally using a white PVC exhaust. With that setup you will notice the savings with your gas bills.

When selling the house the main thing that matters is that it will be a newer system. A selling point could be a higher efficiency unit for some people. Very few would care if it was 2 stage.
 
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Old 12-09-15, 06:34 PM
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80% is gone in canada. In the us only a few reasons to get one: warm climate, furnace installed in attic or garage, furnace in middle of finished basement with a dry-walled ceiling.

u're right though, home buyers don't care about the furnace, only the kitchen and finish materials to impress their shallow friends.

A reason not to get 2-stage is having ducts in an unconditioned space; the longer run times of these furnaces may increase thermal duct losses.
 
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