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If I have an "GMPN100" furnace that is 12 years old, what efficiency% is it?

If I have an "GMPN100" furnace that is 12 years old, what efficiency% is it?

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  #1  
Old 09-25-13, 04:48 PM
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If I have an "GMPN100" furnace that is 12 years old, what efficiency% is it?

I know we can only guess but what do you folks think? I don't see an "85%" efficient, etc, marked anywhere. I'm wondering just how efficient it is compared to a new 97% one I might buy now.

Thx.
 
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  #2  
Old 09-25-13, 05:17 PM
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GMPN100-4 is probably the model you have and is rated at 90+ (92.6) percent efficiency.
 

Last edited by firedawgsatx; 09-25-13 at 05:46 PM.
  #3  
Old 09-25-13, 05:39 PM
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Yes....looks to be a 90% eff. condensing furnace. See page six in link below.

Goodman service info
 
  #4  
Old 09-26-13, 05:54 AM
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As always, thanks to the quick reply, guys! If I switch, I'd be exchanging my 92% efficient furnace for a 97% one. I don't think I'd recoup the extra expense for a long time--if ever--for such a small difference. What do you think?

I've heard 80% an less should always be swapped, at least in the Midwest where I live (Utah).
 
  #5  
Old 09-28-13, 02:58 PM
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The difference between 97% and 92% is 5%. So you'd save about 5% on your heating bills. You have to figure how much gas you use for heating and not for other purposes such as water heating or ranges and dryers. If the ONLY reason you're considering swapping the furnace is to save money, then it's likely you'll never recoup the cost of the swap.

There are still valid reasons for keeping an 80% efficient furnace. It may be financially unfeasible to install the plastic vent piping for a high efficiency furnace (as it is with my house) and the higher the efficiency, the higher maintenace and repair costs will likely be. My mother's 90%+ furnace goes through a heat exchange every 5 years, and the costs to replace them are greatly more than the small amount of gas she saves, compared to her old furnace.
 
  #6  
Old 09-28-13, 05:25 PM
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Beachboy
If your mother's heater goes thru a heat exchanger every 5 years, there is a major problem somewhere. Most likely the furnace has too much capacity for the attached ductwork.
 
  #7  
Old 09-28-13, 05:31 PM
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It's not worth changing unless the heat exchanger is bad and there's no warranty left. Goodman furnaces were apparently not great 12 years ago (they don't build em like they used to, and that's probably a good thing), so you might want to get it checked out.

As for high efficiency furnaces needing more maintenance or "going through heat exchangers every 5 years", it's total nonsense. Mid and high efficiency furnaces share the same key parts (primary heat exchanger, all controls) but 90%+ models have a secondary heat exchanger. Undersized ductwork and improper installation/setup/maintenance kills furnaces regardless of efficiency.
 
  #8  
Old 09-29-13, 07:56 PM
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I have no idea why my mother's Heil furnace goes through heat exchangers every 5 years, but it was installed by an authorized dealer and is being serviced regularily by them. The heat exchanger SHOULD be under either a 20 year or lifetime warranty, and warranty covered it the first time, but not the second time. I've written Heil about the heat exchanger warranty problem, and didn't get much satisfaction.

Also, the installer has told her she cannot turn on the heat without them checking the furnace first, and cannot switch from heat to A/C and back again. So she heats the house with electric heaters until the service agency gets around to checking her furnace. I'm not happy at all with the situation, but she refuses to make a fuss, since she lives in a very small town. She doesn't want to put any more money into replacing the furnace, as she doesn't plan on living there over a couple more years.

I don't mean to highjack the OP's thread, but based on her experience with an early generation condensing furnace, I would never consider one for my own house. I went with 80% when I replaced my own furnace in 2006.
 
  #9  
Old 09-30-13, 01:20 PM
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I'd be willing to bet a month's pay the furnace is not installed right.
 
  #10  
Old 10-01-13, 07:53 AM
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Ok, so back to "MY" thread (j/k).

Here is my updated story and I'd love to have some opinions from as many as possible.

Facts:
- Home is 4100 Sq feet rambler.
- Finished basement with insulation on walls and ceilings.
- 15 vents upstairs. 2 return registers upstairs (large and on the floor)
- 11 vents downstairs. 1 large basement return and 1 medium size in a bedroom.
- Bedrooms (up and down) furthiest away from the furnace room share ducts. Lame, I know. They suffer from poor flow and do get colder than they should.
- Upstairs is vaulted in every room with significant windows in main kitchen and family room. New insulation was blown into attic 2 years ago.
- Current furnace is GMPN100-4 that is 92.6% efficient. Installed in 2001.
- It vents in a way that does NOT pass code. Quotes to vent it properly have been given to me as low as $650 and as high as $800.
- Furnace is a 100,000 BTU.
- Live in Utah, so winters can get rough.
- Had 3 separate quotes for new furnace installation or just fixing bad venting. 2 came in similar one came in $500 less. Each was for either Carrier or Lennox 95% or 96%, 2 stage w/ variable motor furnaces. All included in price the properly run ventilation pipes.

Questions:

My GMP is still running; it's 13 years old, so one has to wonder for how much longer it will keep working. I don't like the venting issues; however, we've dealt with it for 6 years. I could deal with it for a few more. My debate is replace furnace now or wait till the GMP finally gives up the ghost.

I suppose I have 2 questions:

1) How much more comfortable will a new, variable motor furnace make my home--assuming it is installed correctly? All 3 of the bidders saw my current installation and shook their heads. Each one, individually, said the idiots that put this in when the home was built put too small of a return air exchange system in and I have really bad air flow and horrible filtration. The current system is a 1 inch 20x20x1 filter for a 100,000btu system with a 4 ton AC unit connected. All 3 said that is a shame. They all told me that return ducting needs to be replaced and each included that in their quotes.

2) Would you personally wait till the furnace dies or bite the bullet now? With local utility credits and tax credits, I could get a 95% furnace with variable speed motor--properly installed and vented through the roof, for about $3K. It would be a LENNOX EL296V, by the way.

Thoughts?
 
  #11  
Old 10-01-13, 07:13 PM
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In my opinion, correcting the venting & duct issues alone would be worth the $3K. Goodman furnaces do not have a history of being very forgiving when it comes to lack of ducts, particularly on the return side. If it were me, I'd go for it.
 
  #12  
Old 10-01-13, 10:55 PM
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That actually sounds like a pretty good price. My vote would be to change it too.
 
  #13  
Old 10-03-13, 08:01 PM
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If your comfort problems are caused by short cycling, the two stage will help.

If lack of airflow or lousy ductwork is the issue, it won't.
 
  #14  
Old 10-15-13, 11:46 AM
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Ok, time to update the crew. Not sure if this should be a thread of its own. My local crew that I contracted is installing my new furnace and revised return ducting and filtration system.

I took a look at the goodman furnace, that is on its way out. Check out the photos. 4 of the 5 heat exchangers have visible cracks in them.

Wow, so this WAS a good time to replace my Goodman. Keep in mind this furnace is only 12 years old. Shame.
 
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  #15  
Old 10-15-13, 07:46 PM
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Chances are those cracks are directly attribuatable to improper ducting. Don't blame the equipment. Blame the installer.
 
  #16  
Old 10-15-13, 08:37 PM
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Can you explain, Grady? How does improper ducting cause the exchanger to crack? Too little flow causes the metal to get too hot?

If that's the case, would a new installation with a completely revised return system (heater is up higher with much more flow below the fan for more even distribution) help? Or could it be ducting on the other end where it's too hard to push heated air out?
 
  #17  
Old 10-15-13, 08:55 PM
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Improper ducting will cause a furnace to overheat & often does cause heat exchanger failure.
Ducting a a balancing act. You need sufficient supply and return. Too much restriction on either end will cause probems.
 
  #18  
Old 10-16-13, 08:32 AM
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Grady:

So if I have a 4100 Sq. Foot home, rambler with full built out basement that is well insulated, and I like to try to warm up the basement a bit in the winter, is closing vents upstairs an issue? I wouldn't close ALL vents, just 3 or 4 out of 16 total. However, I'd have all basement vents open.

Our basement is often 10 degrees colder than the main floor. I do NOT have a door that can close off the two floors; our stairwell is wide, big and makes both floors feel like one. I know simple physics makes the temperature differences and simply always will; however, if I try to compensate a little by closing a few upstairs vents in the winter is that potentially damaging to my furnace?

16 vents upstairs and 10 vents downstairs. Upstairs I have 2 large return registers and 1 small one. Downstairs I have 2 large return (1 at base of stairs). 90,000 BTU furnace, dual stage being installed today.

Home was built in 2001. Double pain windows but upstairs has some very large windows, while basement are the usual.
 
  #19  
Old 10-16-13, 12:38 PM
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<<
Grady
Improper ducting will cause a furnace to overheat & often does cause heat exchanger failure.
Ducting a a balancing act. You need sufficient supply and return. Too much restriction on either end will cause probems.

Read more: http://www.doityourself.com/forum/newreply.php?p=2165506&noquote=1#ixzz2huoFa3jF>>



Grady's comments here are on target.


Closing too many warm air vents CAN cause the furnace to overheat. This is a fairly common problem. Having too many vents on the main floor open can cause too much heat to go to the first floor, leving not enough for the basement.

Balancing the distribution of the warm air supply to serve both floors properly and still have proper air flow through the furnace isn't something I'd recommend you try with the large number of warm air vents you have. The probability of making things worse is pretty high.

Best to have a good repairman check that out, in my view.

MANY times I've had people who had problems like yours or worse and I've been able to correct the problem Changing the fan speed might also be necessary to get thing working right.

Another possibility is that the duct system is inadequately designed and can't be made to work properly.

But you need a competent repairman to check things out, in my view.
 
  #20  
Old 10-16-13, 02:05 PM
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At least on these forums, the gmp is known to be a crappy furnace so the ductwork might be okay.

Make sure that they checked the temperature rise and gas pressure upon startup - otherwise, you'll be going through this exercise again in 12 years.
 
  #21  
Old 10-16-13, 03:23 PM
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Absoultely nothing wrong with the GMP or any other piece of equipment out there. Just crappy installation/operation.
Twenty three years ago, I wanted to install A/C in my own house. I bought the eqipment with the worst reputation on the market & installed it as it should be done. I have exactly ZERO dollars in repairs & the only "maintenance" it gets is to hose down the condenser once or twice a summer & change filters as needed.
 
  #22  
Old 10-16-13, 05:28 PM
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^You're right, except some can probably take more abuse than others.
 
  #23  
Old 10-16-13, 05:45 PM
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No debate there, Muggle. Case in point is the older Goodman heat pumps. If they didn't have enough return, it was bye-bye compressor.
 
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