Replies

1. 
   hvacnut | Oct 20, 2002 07:18am | #1

   John, I think you may be getting some of the terminologies used with the new furnaces confused. Variable speed has to do with the air flow through the furnace. Most of the manufacturers also match these blowers up with 2 STAGE  burners, not 2 speed. Am I right or are you asking about 2 speed blowers?

1. 
   JohnHens | Oct 20, 2002 07:37pm | #2

   I went on the Carrier website and they featured both variable speed and 2 speed

   blowers. There was a difference in price and I was wondering whether there was

   enough of a performence difference to warrant the price difference. I understand

   that there is a supposed electric savings over a year to recoup the additional cost    

   of a variable speed furnace over time, but if the performence is comparable to a 2 

   speed blower, why spend the additional money? What is the reliability/ life of  the

   variable speed vs the 2 speed blower?  Thanks  

2. 
   Chicagobob | Oct 20, 2002 07:44pm | #3

   I have the same question, as I will be in the market for a forced air furnace in the near future.  I heard a commercial over the radio which described a furnace, (I think the brand was Trane) which compared heating your house to driving your car.  When you drive, you don't floor the pedal, and then ease up, then floor it, then ease up, etc.  They stated you should not do the same for your house either.  This furnace runs the blower at a lower speed (and maybe less gas) and then when the house needs heat, the furnace kicks it up a notch.  Is this a new technology?  Is it a good solution compared to  normal furnaces?

   Thanks,

   Bob

1. 
   hvacnut | Oct 21, 2002 04:06am | #4

   I went to Carrier's web site and I can see where you are confused, they are a little loose with their wording. Let me describe how these 2 STAGE, or 2 speed as Carrier calls them, furnaces work. They use a special 2 stage thermostat to activate either of the furnaces stages. During mild weather the furnace's gas control opens to it's low setting which is typically 60% of the high setting. This makes the furnace produce an amount of heat that more closely matches the requirements of the home, which in turn makes the home more comfortable by running longer and better circulating the warm air throughout the house. When the outdoor temperatures drop, the thermostat will detect the need for more heat and bring the furnace to high stage. These furnaces have been in use for more then 10 yrs with great success. Now let's talk blowers, these furnaces are available with either a standard multi-speed blower or a true variable speed blower. The standard blower typically has 4 speeds to choose from and your installer will set the furnace to use just 3 of them, one for low heat, another for high heat, and the third for air conditioning. A true variable speed blower is capable of running at any speed from very, very slow to very, very high. Your installer will actually program the blower to move a certain amount of air in cfm (cubic feet per minute) and the blower will set it's speed accordingly taking into account your complete duct system and even the cleanliness of your air filter. These variable speed blowers also offer greater energy savings by being more electrically efficient then the standard multi-speed blowers. I can tell you from my own experience that these variable speed blowers are much quieter and make your home more comfortable then the standard ones because I have had one in my own home for about 6 yrs. I think they are well worth the extra money. Their dependability has been excellent, however the repair parts if you ever need them, will cost more then the standard blowers so you may want to check out the warranty and possibly get an extended warranty on them.

2. 
   TLRice | Oct 21, 2002 03:13pm | #5

   John,

   I have been designing and specifying systems with variable speed furnaces (whenever the project budget allows) for years and I finally got one for my house just recently. My house is under going a considereable renovation and currently the furnace is in a very exposed location. Every furnace sound is readily observable. Compared to the unit that was replaced, it is very quiet. The combustion fan is as loud as the the main blower, not that the combustion fan is loud, just that the other is quiet.

   The pros: greater control flexibility, quieter, more energy efficient. Variable speed blowers are, in residential furnaces, usually if not always, packaged with two-stage, high efficiency furnaces. The increased cost is not just in the blower drive, but in the entire unit, which tends to be the high end of most product lines. You get better heat exchangers, cabinet insulation, a better gas valve, and better controls.

   The cons: greater upfront cost, "need" for a two stage thermostat. The 2-stage stat is not a requirement, but it is a good idea. Other than the cost, the sound that the DC motor makes ramping can, in certain ranges, produce some odd sounds due to harmonics. These sounds are less noticeable than the typical sound of a PSC (standard) blower starting.

   The difference is cost between a 92% efficient 2-stage with a mulitispeed vs. variable speed will be paid back over the life of the unit in decreased fan energy usage alone. The rest is "extra" benefits. I highly recommend the variable speed furnace over any other.

1. 
   JohnHens | Oct 21, 2002 06:49pm | #6

   Tim,

   Thanks for your reply to my question. It is always helpful to get actual imput

   from an enduser especially if the person is in the business.  

3. 
   whoover | Oct 21, 2002 08:51pm | #7

   I know several people who have furnaces with a variable speed blower and claim they will never, ever go back to fixed speed or speeds no matter what the cost!  The quiet and comfort can not be matched.

   Bill