Replies

1. 
   Virginbuild | Feb 09, 2007 09:41am | #1

   Hi Charette

   Ref:  It cycles on and off quite a bit.

   Reasons are It is darned cold outside :-) , House is poorly insulated, furnace is over sized for heated area, and possibly the anticipator in your thermostat is not adjusted correctly. also; noise factor could be caused by improperly installed isolation dampers between the plenum and the duct runs.

   I have Carrier Infinity furnaces installed. The are infinitely variable speed furnaces and they are very quiet. At full rate burn and full delivery capacity the noise naturally ramps up a bit which is rare because they usually operate at lower settings and at longer run times. I am very well satisfied with the units that I have. 

   By the way; my fuel bills dropped fifty percent when I installed the Carrier Infinity units.

   Do evaluate your geographic area for heating degree days, your house construction, The tightness of your house for air infiltration, Insulation "R" rating and insulation type, in addition to the health of your present heating system.

   Regards,

   Virginbuild

2. 
   lcdeyes | Feb 09, 2007 10:30am | #2

   A "yes/no" response cannot be justified without knowing the system age, condition, state of maintenance, design and installation quality of the ductwork. The location within the house, common walls, and furnace sizing are also a big factor in answering your question. Even the register grills can add noise.

   As far as "cycling on and off" frequency, that could be due to the weather, house construction, oversizing the furnace (typical), or a mis-adjusted limit switch.

   That said, a variable speed unit is usually perceived as more quiet since the blower will operate at a lower speed than a single speed unit, until the heat demand is not met within a time limit. Also, for those who operate the fan continuously (suggested for comfort) the drive motor in the variable speed unit is much more efficient and runs at an even lower speed in the continuous fan mode, decreasing noise. In my opinion, that is one of the better reasons to go with variable speed.

   Do not assume that buying a new variable speed furnace will solve the noise issue entirely. If the furnace has a common wall to the family room, for example, a 90% plus unit will add the noise of the condenser fan, which is higher pitched and can be even more annoying than the blower fan. Generally, my preference are the 80-85% units if possible.

   There are more than enough hack outfits who will gladly replace your furnace. You might just need your system cleaned and serviced. Otherwise, try to find someone who will take the time to diagnose and advise you competently without whipping out the new furnace brochure. Don't expect that kind of professional for free.

   On that note, good luck- the residential HVAC business is a can of worms.

   
   

   ---

   Edited 2/9/2007 2:33 am ET by lcdeyes

3. 
   DanH | Feb 09, 2007 02:05pm | #3

   Too little info. Are you talking about swapping out just the fan, or the entire furnace?

   If just the fan: How do you propose to adjust the speed of the fan? How old is the furnace? What's its claimed efficiency?

   What do you mean "cycles"? Is just the fan going on and off, with the burner still burning, or is the entire furnace cycling? If the motor only is cycling then likely (in a conventional furnace) the fan/limit control needs adjustment. If the entire furnace is cycling then either the furnace is simply too large or you need to adjust the anticipation setting on the thermostat.

   Note that there are "multi-speed" fans that have speed changed by selecting taps on the fan, and "variable speed" fans that are DC fans driven by a variable voltage circuit. The latter style must be matched to the control board, but uses much less electricity than a standard fan motor.

   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
1. 
   charette | Feb 10, 2007 07:11pm | #4

   Since my posting I have discovered the complications of going to a variable speed fan, ie DC conversion, different controls.  It seems that the variable speed fan option would most reasonably be installed with an entirely new furnace.  My current furnace is but six years old, so I have taken variable speed off the table.  Do you agree that a variable speed unit would run quieter?

   I am now looking at wiring options on the existing fan to slow the speed and thereby quiet it and have it run for a longer time.  I see two potential problems: overheating of the burner and the cost tradeoff between gas and electricity with the longer run time.  Other than the cool down period after the thermostat is satisfied, I presume that the burner is on while the fan is on.  Do you see any other considerations?

1. 
   DanH | Feb 10, 2007 08:45pm | #5

   You'll mess up the furnace efficiency, especially if you don't cut down the burner flow.What's bothering you? The sound of air rushing, or vibrations from the fan or something else?
   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin

1. 
   charette | Feb 10, 2007 09:38pm | #6

   Thanx.  My main complaint is the noise from the air flow.

1. 
   charette | Feb 10, 2007 09:42pm | #7

   virginbuild,

   are Carrier Infinity units high efficiency? 90% or above%?

2. 
   lcdeyes | Feb 10, 2007 11:56pm | #8

   In a new tract home, I once had a rushing air noise problem from a register in my den. The noise was caused by the duct being close to the furnace, so there was too much air volume. There was also poor ducting technique (panning the joist space instead of using duct), allowing the air to whistle around some floor structure prior to entering the room through an undersized register.I solved the problem entirely by doing three things, one or more of which might help. A manual damper was added to that room's supply duct (where it attached to the main trunk) to lower the air volume, which was too high for the small room anyway. A 4 ft length of R-8 insulated flex duct was substituted for some of the joist panning after the new damper. (I had access from the basement). The remainder of the panning was not accessable. The flex duct does not transmit noise as much as sheet metal does.Lastly, I bought several square feet of sound-deadening mat from the local sheet metal shop and used contact adhesive to glue it on the INSIDE walls of the plenum directly under the register. To do this I reached through the register opening. The mat is the same stuff you find on the interior of your furnace's blower compartment, and is approved for this kind of use.After all this I couldn't hear the air at all, and my desk was only a few feet from the register.No doubt your situation is different than mine was, but I thought I'd provide a few ideas to help you or someone who has a similar problem.