Two stage furnace or Variable speed fan worthwhile?

[Carrie Simpson]

I'm replacing my natural gas furnace with a modern one and am considering a 92% AFUE single stage furnace, a ~95% AFUE 2 stage furnace, or a 2 stage furnace w/ a variable speed fan. There is a $400 utility rebate for the variable fan furnace, and a $150 utility rebate for the others. Prices are about $3700 for the 92% single stage, $4200 for the double stage, or $4400 for the variable speed furnace. For simplicity, these estimates are for one brand (American Standard) but other brands are similarily priced. All work will be one by a reputable established HVAC firm.

My house is about 1800 sq ft. Is it worth it to get the two stage and/or variable speed model (w/ an ECM motor)? Are they any less reliable? I assume they will have higher repair costs if they are. I understand that GE makes the ECM fan motors for most furnace companies. I'm also considering replacing the old inside (evaporator) A.C. coil for $400 now while the ductwork is being worked on, with the expectation of replacing the outside unit with a matched Am. Standard model in a few years.

Am. Standards also has a free humidifier in my area offered with the variable speed unit, although I'm not sure I need that-due to condensation on the cold days when you want the humididy. Thanks for any advice!

[Carrie Simpson]

I'm replacing my natural gas furnace with a modern one and am considering a

92% AFUE single stage furnace, a ~95% AFUE 2 stage furnace, or a 2 stage furnace w/ a variable speed fan. There is a $400 utility rebate for the variable fan furnace, and a $150 utility rebate for the others. Prices are about $3700 for the 92% single stage, $4200 for the double stage, or $4400 for the variable speed furnace. For simplicity, these estimates are for one brand (American Standard) but other brands are similarily priced. All work will be one by a reputable established HVAC firm.

My house is about 1800 sq ft. Is it worth it to get the two stage and/or variable speed model (w/ an ECM motor)? Are they any less reliable? I assume they will have higher repair costs if they are. I understand that GE makes the ECM fan motors for most furnace companies. I'm also considering replacing the old inside (evaporator) A.C. coil for $400 now while the ductwork is being worked on, with the expectation of replacing the outside unit with a matched Am. Standard model in a few years.

Am. Standards also has a free humidifier in my area offered with the variable speed unit, although I'm not sure I need that-due to condensation on the cold days when you want the humididy. Thanks for any advice!

[m Ransley]

VS DC are 50- 75% more efficient motors, they do break so get the 10 yr warranty. On Carrier and Lennox you can get a humidistat- thermostat and run it real slow to remove more moisture in AC mode. You can also get more even heat by running low in heat mode. 2 speed also gives more even heat . But I like te electrical savings and options with VS DC. 400 rebate on VS DC! Go for it, It can take those 74 degree days that are humid and be set to remove humidity.

[SQLit]

My last home had an AS with an vfd motor. It had preprogrammed steps that it followed.

0%-30%-80% then if needed 100%. Same for shutting down. My primary load was cooling and I noticed that when the motor actually went to 100% it was pretty loud. It did not go to 100% very often. Better check the programming of the units. You may be mis-informed about how they work. I purchased the vfd for humidity removal, which it did very well. Are the SEER numbers greater with the 2 speed and or the vfd?

[MLD]

I opted for the variable speed motor (got a $400 rebate for this model). I find that it has worked out very well and is worth while. Especially during the cold weather, it seems that the system operates mostly on the first stage, low fan speed, more often than not. This has resulted in a more even heating and a more comfortable house as compared to the off/on cycling of the older furnace which allowed the house to seemingly cool off between cycles. MLD

[John Davies]

If money is the motivator of the decision you have to figure the energy cost savings vs the number of years you think you will be living in the home. A fancy furnace adds only minimal resale value to the home. Is the extra cost worth it? Only you can answer that question.

The two speed and variable speed fans make for a much more comfortable environment. The two speed version will only kick onto high speed if the house does not warm up quickly enough to satisfy the thermostat in a certain amount of time (14 minutes I believe for Trane). The variable speed model adds a nice feature in that it ramps up to speed slowly and smoothly to reduce cold drafts. Both features reduce electrical and gas usage. I don't know if all brands offer multi-stage burners, but that is nifty because only the smaller initial stage runs unless you need max heating.

I really like my Trane variable speed furnace. It has a 10 year warranty so repair costs are a distant worry.

Don't expect an upgraded coil to work well with your old compressor - the two need to be matched for optimum efficiency. I would wait on the coil until you can replace both parts at once.

That's why you either get a manual humidistat and remember to adjust it according to outside air temp, or get an automatic one. Controlled humidity in winter makes for a more comfy place to live, and your furniture and hardwood flooring will last longer. My suggestion is accept the free humidifier and add a good control. If manual, have it placed right next to the main thermostat, not on the furnace.

John

John Davies TLCA 14732

'96 Lexus LX450 '00 Audi A4 1.8T quattro Spokane WA USA

[TURTLE]

This is Turtle.

Veriable of two stage seem to be good but if you choose the Veriable. Get the 10 year warranty on the furnace because your odds of the veriable speed motor messing up is good in the first 10 years of service.

In any case I do like the two stage heat and the 90% afue or better but I concider the veriable speeds just a option. Now I concider the Veriable option as just a cooling deal and not any real help on heating.

TURTLE

[m Ransley]

Turtle what about the fact VS DC motors consume 25-66% less power. That saves winter and summer on operation.

[toller]

The variable speed have a great property beyond HVAC efficiency/comfort. They have no startup current draw. That is great if you are trying to power your house off a small generator; you don't have to worry about the furnace coming on and overloading the system.

This might not matter to you, but it does to me.

[TURTLE]

This is Turtle.

There maybe a little saving on electric cost but i change a set speed motors for about $185.00 to $235.00 and then change Veriable speed motors in the ball park of $800.00. The saving went out the window with even a veriable going out every

10 years or so.

TURTLE

[m Ransley]

Well they have been redesigned to last longer, the circuits have been separated from the motor housing to reduce heat failure. It is to early to tell of longevity with the new design, but it will be better. So that is why the 10yr warranty should be taken. But asides I calculated a 120-145 a year savings in electrical usage at my .1250 Kwh cost a year giving a 5-7 yr payback at todays electrical rates. I expect rates to go way up in 5-10 yrs perhaps double. Therefore lowering payback time .

Increased comfort, programability, more humidity removal, a new motor design, more efficiency are worth it with a 10 yr warranty. But just considering electrical savings and a good payback make it worthwhile