High Efficiency Furnace

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Old 05-12-10, 09:42 AM
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High Efficiency Furnace

Hay all,

I am new to this forum, I joined because I have to make a decision about buying a new forced air furnace for my home, I also decided to install central air as well. I am looking into the new 92% high effect system. The mechanic that is going to install the system seems to think this is not a good idea to go with the 92% system as the they are more expensive and the parts are costly making ongoing maintenance an issue. My first question is, will I really save money in the long run? In addition these systems are so new does any one have any idea how they hold up in the field? Can I expect the same 34 years of service I got out of my old furnace?

Also does anyone have knowledge on the install? I think the mechanic wants me to purchase an 80% legacy system because it seems he does not know much about installation of high efficiency systems. He did say I'd need a dual stage thermostat, and that PVC had to be run out the foundation, and that I could not use my chimney. I assume there are local laws especially here in the suburbs of NYC governing some of this issues, any info would be greatly appreciated.
 
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Old 05-12-10, 04:28 PM
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Horses eat hay.

There is not much that is new with the 90+% furnaces, they have been around for at least twenty years in one form or another. What may be considered newER is the two-stage burners and the variable speed blower. There are some furnaces today that offer more than just two burner stages.

Installation wise all of the 90+% furnaces use PVC pipe to exhaust the products of combustion outside the house and none of them use a conventional chimney. The better units also bring in outside air for combustion so as to not upset the pressure balanced between the inside and outside of the house. They all need a condensate drain, either a floor drain nearby or a pump/tank unit nearby that can pump the condensate to a drain. This condensate is the result of cooling the flue gases to a point where the water vapor generated by combustion is condensed to liquid water.

The only parts a 90+% furnace would have that an 80% would not are the secondary heat exchanger and some fittings along with the plastic (PVC) exhaust piping. Heat exchangers were a failure point in the first (0+% models but that has been taken care of in current models. Heat exchangers will also have a pretty decent warranty, anywhere from 25 years to lifetime.

The two-stage gas valve and two-stage induced draft blowers are pretty reliable so there shouldn't be any problem with them. The variable speed room-air blowers are fairly reliable but if the motor craps out (usually due to a $3 part) the entire motor is about $1,000. On the plus side they don't crap out all that often.

There are 90+% furnaces available with only a single-stage burner but I wouldn't buy one. The beauty of the two (or more) stage system is that in milder weather (more than 80% of the time) the furnace will fire on the first stage and will run for a longer period of time. This not only saves fuel it also is quieter and makes for a more comfortable temperature maintenance. The variable speed blower enhances this comfort.

Will you save enough to justify the 90+% furnace over an 80% model? It really depends on how cold it gets and for how long a period in your neck of the woods. I live in a suburb of Seattle where temperatures below freezing are rare and it is almost unheard of for the temperature to drop to zero or below. In my climate it would generally take at least ten years (or likely more) to just break even by buying a 90+% furnace. In your climate it might take only a couple of years. Remember that through the end of the year there is a tax credit for purchasing a 90+% furnace and also a credit for the higher efficiency air conditioner and if you are able to take advantage of this credit that can be applied immediately to the return of investment on the higher efficiency units.

As for longevity I can assure you that no furnace you install today will last for 34 years. The average lifespan of a furnace is about 20 years with some lasting a bit less and others lasting a bit longer. Generally the workmanship of the installation is more important than the make of the equipment.

Whatever you decide be sure that your contractor does a complete "heat-loss / heat-gain" calculation on your home BEFORE sizing the furnace or air conditioning. He must also make certain the ductwork can support the cooling system selected. DO NOT size a new furnace from the old furnace as the existing furnace is almost certainly oversized. Also, do any work to reduce heat loss / heat gain such as additional insulation, weatherstripping, new windows, and the like BEFORE sizing the heating and cooling equipment.
 
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Old 05-15-10, 08:54 AM
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I'd look for another dealer.

Furd did a good job going over things here.

The 90% don't have that much more parts than 80% would have. Just one extra heat exchanger as Furd said.

With you being in the northern states, the 90% will see a pay back on it.

I'm with on the home updateing of new windows and what not. I am in that myself. We had our windows done last year, now my A/C is ovesized by half a ton..
 
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Old 05-17-10, 12:22 AM
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PVC sugestion

I think you are getting great advice here. The weatherization steps before you do the duct blast, etc test are especially important to get a fast pay back from your higher efficiency furnace.

Anyway, as you install the condensing furnace (90+ efficiency) take a look at the following intake/exhaust PVC solution. Could make things easier.

http://www.hvac.amickracing.com/Furn...ll%20Guide.pdf
 
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Old 05-17-10, 10:02 AM
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My own experience with high efficiency gas furnaces is that they cost more to own over the life of the furnace. And don't expect to get anywhere the 34 years of life you got out of your old furnace.

I installed an 80% efficiency furnace in 1994, which had the induced draft blower and a computer control. In the 12 years I owned that unit, I had to replace the induced draft blower assembly, computer control board, fan motor relay, flame sensor, and ignitor. The few dollars in gas that I saved over my old 60% efficiency furnace paled in comparision to the money I spent on maintenance on the new furnace. And after 12 years, I had to replace it.

I had my HVAC tech to my house last Friday to check out my A/C unit and I asked him about high efficiency HVAC equipment and the government tax rebates. He said their company didn't recommend the super high efficiency equipment, as repair costs were high. He said the variable speed blower motors commonly touted failed quite often and cost well over $500 to replace.

If they were still available, I'd go back in an instant with a 1970's era standing pilot conventional furnace. The $10-$25 a month it cost me in additional gas would be offset by the savings in maintenance and the greater reliability. Oh yeah, did I mention my new furnace rarely ran a whole winter without some sort of electrical breakdown? Usually during the coldest part of the month and on a weekend or holiday. I'm definitately not a fan of high efficiency/high tech equipment.
 
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Old 05-18-10, 05:17 AM
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I claim no expertise with HVAC but I have done a lot of research and spoken with many experts in the topic as well as weatherization.

The variable speed (ECM) blower motors can and do save significant $$ on electrical usage, they are also really flexible during heating season, when many chose to run their furnace fan 24/7 to even out the warm/cold spots in the house. With and ECM motor, the high efficiency furnace will run the blower at a slower and quieter speed - which on an ECM motor saves operating $$. Reliability was an issue with these motors early on (which are still out there in older, high efficiency furnaces. Those motors were not protected from electrical power surges. Late model ECM motors include metal oxide varistor(s) to absorb the surges. These motors are more expensive than traditional motors and I believe some/most residential HVAC/furnace manufactures charge approximately 3 times the price of these motors. Most of the failures happen in the electronics end of the motor and are surprisingly inexpensive to fix. The problem is, when the motor fails, it does not give warning sounds like a failing bearing, etc. But, these GE motors are much more reliable now.

High efficiency, condensing furnaces have a far more reliable (and quieter) combustion vents compared to the 80% power venting combustion furnaces. A huge difference.

Because the condensing furnace drains the (acidic water) condensate to drain, the heat exchanger is not exposed to the damaging oxidation that less efficient furnaces.

Before you choose your furnace, do not assume that that your existing duct work is correct, both the return and the supply duct size needs to be evaluated.

Finally, one of the best ways to preserve a furnace is to weatherize the home, including sealing all vents and ducts, sealing _all_ openings between the living space and both the attic and the basement/crawl space, and insulating up to R-30. After doing that work, get an air infiltration test and a duct blaster test so you know what else needs to get sealed up and it will help to know the size (BTU) and A/C tonnage your will need.

Good Luck.
 
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Old 05-18-10, 06:19 PM
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It has been six days since the original post and that poster has not returned. I think it is safe to call him a one-post wonder.

I just knew I shouldn't have wasted my time in a long response.
 
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Old 05-18-10, 08:21 PM
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... but I get over it ...

My philosophy is to reply so future readers can learn from my experience. But I agree it is disappointing how few folks who pose questions come back with an update.

No closure .... but I get over it.
 
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Old 05-19-10, 04:11 PM
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Originally Posted by furd View Post
It has been six days since the original post and that poster has not returned. I think it is safe to call him a one-post wonder.

I just knew I shouldn't have wasted my time in a long response.
I knew that too, and was surprised since......didn't you start a thread by that title in the chat forum?

......I shouldn't have wasted my time in a long response.
I read it. Nice post.
 
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Old 06-15-10, 07:54 AM
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I got a lot out of your reply also. Definitely not wasted effort!
 
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Old 08-08-10, 05:01 PM
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Originally Posted by furd View Post
It has been six days since the original post and that poster has not returned. I think it is safe to call him a one-post wonder.

I just knew I shouldn't have wasted my time in a long response.
Thanks, Furd, you answered quite a few of my questions as well.
Look on the bright side... you can copy&paste your answer for the next one.
 
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