Effificient variable speed 2 stage furnace


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Old 07-16-09, 01:47 PM
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Effificient variable speed 2 stage furnace

Hello everyone, What the difference between "EFFIFICIENT VARIABLE SPEED 2 STAGE FURNACE" -and "2 STAGE FURNACE"? The cost is $500.00 different between the 2 units, so I don't know if it's worth the extra money. If this helps, I live metro Detroit area so It gets cold in the winter. My house is framed and more than 30 years old. Any advice would greatly appreciate it. Ozzie
 
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Old 07-16-09, 02:37 PM
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"Variable speed" is the blower motor that runs on DC power and takes less watage to run it. On an avg. it about 60 to 100 watts vs a standard blower use about 500 to 700 watts.

I honestly think it's worth the extra money for a few reason.

-Less energy is used, meaning lower electric bill.

-Fan runs quieter when the fan is in "Fan On" mode.

-Fan motor ramps up to speed rather "sudden start" up.

-Blower is a larger range of speed to pick and has a better chance to matching your heating and cooling needs, rather than a "Fixed" 3 or 4 speed.

-Variable speed can be tied to a humidistat control for cooling and it will slow down the blower if the humidity in the home is very high, the slower blower helps the A/C pull the humidity out of the air.


I have a variable speed blower on my furnace, and when it's running in first stage heating or cooling, I hardly hear it running, and the furnace is about 10' away from me and I hardly hear it running.


Also with the two stage system. Be sure to get a good two stage t-stat like Honeywell IAQ, or VisionPro. That way with the cold winter, you will run longer in first stage for comfort and quiet, and 2nd stage will only cycle on as needed.
 
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Old 07-16-09, 02:40 PM
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First I will give you a short primer on the different styles/types/models of forced air furnaces.

The first thing is efficiency. The government mandates that furnace manufacturers rate their furnaces under laboratory conditions that are to simulate an average years operation in a typical home. This is called the Annualized Fuel Utilization Efficiency or AFUE rating. All manufacturers must use the same method so the test results are directly comparable across all manufacturers within the same model type. However, this does not necessarily hold true when comparing different model types. Note also that AFUE cannot be measured in the field, it is a laboratory test only. The "efficiency test" done by the furnace technician in your home is a "combustion efficiency" test and while it is an important test it is only a "snapshot" efficiency of the furnace at the exact time of the test.

Very broadly, there are two AFUE ranges; 80+ percent and 90+ percent. Unless you live in an area of mild winters like I do you will most likely want a 90+% AFUE-rated furnace. The 90+% AFUE furnaces are also called "condensing furnaces" because they cool the exhaust gases to a point where the water vapor created by burning natural gas (or propane) condenses in the final heat exchanger. Because of this most of these furnaces do not use a chimney for exhaust but instead use plastic piping that exhausts through a side wall of the house. Some furnaces can be exhausted vertically using an old brick chimney as a "chase" to contain the plastic exhaust piping. These furnaces also use plastic piping to bring in outside air for combustion and this combustion air piping will run either parallel to the exhaust or sometimes concentrically.

Once you get past the AFUE rating you have to decide on the BTU rating of the furnace and how that rating is achieved. In short, the BTU rating is how much heat the furnace delivers to your home. Most furnaces that were installed years ago are oversized, sometimes vastly oversized. When energy saving improvements have been made to a home such as more insulation, weatherstripping, new windows and doors, caulking and the like the heating requirements of the home decrease and that makes the furnace even more oversized. Ideally, a furnace installation company will do what is called a heat loss calculation (sometimes called a manual J calculation) to determine the proper size for a furnace. Unfortunately this calculation is often not done and a replacement furnace of the same size as originally installed is specified. In their defense, if your house is a common one (you live in a development of similar houses) and you haven't made any serious changes in the house since it was built the installation company may have done enough heat loss calculations on similar houses to make a pretty darn guess with your house. Still, if you have made significant changes, say an addition or triple-pane windows you should request a heat loss calculation AFTER you have decided on a particular installer.

I say to request the calculation after deciding on the installer because a heat loss calculation is not a small item. It will take at least an hour and maybe two, for the technician/salesperson to obtain all the measurements of your home to enter into the computer program. This simply cannot be done for free but the calculation should be part of the overall installation. Along those same lines of thought it must be stated that most furnaces are competitive, that is, the installation is really more important than who manufactured the furnace; a "lesser furnace" with a top notch installation will be better than the "best" furnace with a mediocre installation.

On to the different models. Within each broad category of AFUE (80+% and 90+%) there will be single stage, two stage and with at least one manufacturer, multi-stage, burners. What this means is that the furnace has one, two or several "heat output" stages that will be selected by some means, usually the indoors thermostat. Single stage is the simplest and (in my opinion) the least desirable because the heat is either full on or off. This furnace will be most efficient at the coldest temperatures (design temperature) for your locality BUT will fall off in efficiency anytime the outside temperature is above the design temperature, which will be most of the time. To get around this loss of efficiency manufacturers offer the two-stage burner. With this design the furnace will start at a reduced heat output, generally around 60% of full output, and if this satisfies the heating requirement it will never go to the second stage. Of course the furnace may run for a longer period of time but the actual amount of fuel burnt is no more (and usually less) that the shorter run at a higher output. This is true because the first few minutes of the burner operation is far less efficient.
This longer "cycle time" will also promote more even heating and greater comfort, especially when the outside temperatures are significantly warmer than the design temperature.

The other major factor is the blower speed. Standard furnaces use a three or four speed blower that is adjusted once at installation for the closest airflow to meet the needs of the house. Of course this is only approximate because of the limited selection of speeds. The upgrade from this is called variable speed and this utilizes a different motor and control that gives far more choices to the speed and therefore airflow. It also gives two distinct blower speeds for the two stage burner system and has the option of having a very slow speed that can circulate the air when the burner is off for increased comfort and for increased filtering of the air. The variable speed motor is more energy efficient than is the fixed multi speed motor and this can sometimes result in lower electricity consumption.

Then there are several "add-on" features that you might find useful. If you have more questions, just ask.
 
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Old 07-19-09, 09:43 AM
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Effificient variable speed 2 stage furnace

Wow..a lot of information to swallow, but extremely informative. Thanks for all your help. As usual, you can always count on this site for great advice. Thanks guys
 
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Old 07-19-09, 08:11 PM
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Glad to help out.

One thing I forgot to add in my post, I run my fan 24/7 in the winter, also cool weather when the windows are not open. (not on in A/C mode) With that fan on it runs at a slower speed that you don't even hear.

t moves the air just enough to provide comfort, and won't feel the "draft" as you would with most standard blower. For an example in my '68 split level home, all the room up and down are with in 1˚ from another.

And I have a Media Air filter for better indoor air for my allergy.
 
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Old 07-25-09, 06:34 AM
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There would be more comfort with the variable speed DC motor. Although $500 in your pocket provides comfort too. The additional power used by the traditional 2 speed motor would be converted to heat that is in the heating air flow so it wouldn't be totally wasted. I would be more concerned with the 30% federal tax credit.
 
 

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