Modulating Furnace
Automatically makes slight operating adjustments to achieve maximum efficiency
Standard furnaces operate like your car in stop-and-go traffic. Fuel efficiency goes down and you're less comfortable. A modulating furnace is like highway driving, making slight operating adjustments while achieving maximum efficiency. This new condensing furnace with a modulating gas valve operates with more finesse to reduce temperature fluctuations, providing consistent indoor temperature, quiet operation, and an annual fuel utilization efficiency (AFUE) of 94%.
The Classic 90 plus High Efficiency Modulating Upflow Gas Furnace is the first to combine a modulating gas valve with a variable-speed blower. The blower has an ICM2+ (integrated control module) motor, which is more electrically efficient than that of a multi-speed blower. The furnace's gas valve operates between 40% and 100% of total capacity, in 5% increments, continuously regulating the amount of fuel burned according to the thermostat setting. The thermostat and its remote temperature sensors provide feedback for the control board, which uses "fuzzy logic" to vary valve and blower settings.
Heating mode starts with the gas at 100% and the fan at 0%, the valve reducing and the blower increasing until maximum efficiency is reached. The fan then runs continuously, ramping up or down depending upon air delivery requirements. Since the fan and burner almost never run at full capacity and energy-robbing on/off cycling is eliminated, the unit is highly fuel-efficient.
Five models are available with input rates from 60,000 to 120,000 Btu/h. Additional choices include blower size, single or multi zone, remote thermostat sensors, humidifier, air filters, and condensate pump, return plenum, and vent termination.
Installation
The 28" deep x 24" wide (max) x 34" high furnace can be installed in a tight space like a closet. Ducts must be sized correctly for the unit to run efficiently. A standard cooling coil can be mounted on top. Connections for gas and electric and condensate drain are accessed from either the left or the right side. The unit can only be installed by a mechanical contractor certified for this particular furnace. For a four-hour class that costs $125 to $150, the contractor gets installation/operation manuals, an analyzer tool, and certification.
Benefits/Costs
The modulating furnace costs $1,300 to $1,700, depending on size. A conventional furnace with 90% annual fuel utilization efficiency (AFUE) costs about $900. A complete modulating heating system, including ducts, could cost up to $4,000 installed. In comparison, a conventional system with 80%AFUE costs approximately $2,200, and a 90% AFUE system is closer to $2,900.
The modulating furnace is a premium quality furnace. Although the costs almost three times as much as the least expensive furnaces, fuel savings eventually pay for the extra cost. The constant modulation allows consistency -- Rheem claims room temperatures to be within a half degree of the thermostat setting -- and quieter operation. The constant fan operation results in increased circulation and potentially improved indoor air quality. Because the home's air is constantly being mixed, temperature averaging could eliminate the need for multiple zones in some cases. Its self-diagnostics should make servicing easier. |
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Programmable Thermostat
Programmable thermostats save energy by permitting occupants to set temperatures according to whether the house is occupied. These thermostats can automatically store and repeat settings daily with allowance for manual override. By eliminating manual setback, which is easy to forget, they allow the setting of more comfortable temperatures in the morning before occupants wake. Temperature setback can be adjusted for both heating and cooling seasons.
Programmable thermostats can be set to adjust the temperature setting according to a user's schedule. These thermostats typically have a digital interface that allows more precise temperature control and a wider range of options or features.
Programmable thermostats typically offer a number of programming options:
- Daily programming that allows one schedule to be used each day
- Weekday/Weekend (5/2) programming that allows adjustment of timing for setbacks with different settings for weekdays and weekends, and with 5/1/1 programming that permits separate schedules for Saturday and Sunday
- Full seven-day programming that permits a different setback schedule for each day of the week.
- Other special features depend on manufacturer and model and may include the following:
- Vacation Override, which allows temporary override of the programmed settings.
- Keyboard Lock, which prevents unauthorized changes to the pre-programmed settings.
- Low Battery Indicator indicates whether the battery used to hold the programmed schedule is low.
- An Energy Monitor that can keep track of how many hours the HVAC system has run for any selected time period
- An Auto Season Changeover that automatically provides heat or cooling at the onset of the heating and cooling season
- A Filter Change Indicator that goes on after a pre-set time period to remind when it is time to clean or replace the filter
Different types of heating/cooling systems may require different types of programmable thermostats. For example, heat pumps require programmable thermostats that minimize the use of less efficient auxiliary electric resistance heating. Only a few companies manufacture line-voltage setback thermostats that directly control 120 volt or 240 volt line-voltage circuits connected to electric baseboard electric heaters. When purchasing a programmable thermostat, it is necessary to insure the thermostat is compatible with the HVAC system.
What you just read on this page above you can easily find on a lot of websites, but almost nobody would tell you about another one very important feature of the programmable thermostat:......
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Infinity Control™ SYSTXCCUID01
Infinity / Evolution Sequences of Operation
Programmable Comfort Control
The Effects of Thermostat Setting on Seasonal Energy Consumption at the CCHT Research Facility
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30. Thermostat Wiring* – the chapter talks about thermostat wiring and describes how to run thermostat wires at the  Rough-in.
The chapter has 2 picture; 2 page. $2.00 (Instant Access).
*Artyicle:
Thermostats
On 08.03.2011 text of this chapter was significantly modified and improved.
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53. Thermostat Installation* – the chapter gives a brief description on the thermostat installation.
 The chapter has 3 pictures; 1 page. $1.86 (Instant Access).
*Table:
Conventional heating, air conditioning and heat pump thermostat wiring labels, wire color codes and the corresponding function description.
Infinity Control™ SYSTXCCUID01 - PDF file
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Question
I have a Goodman GMH950703BX 69,000 Btu 95 % Furnace. My question is I normally set the Thermostat at 67 and it seems like the air is not that warm when you feel down by the vent, but if I go out side or don’t pay attention to it went it kicks on the house feels fine. The other question I have is My bedroom is above the garage and it seem that at 67 the room is cold but at 70 the room is fine is there a way I can program the furnace to burn at the high temp so I can run at 67,or is there not that big of a difference from 67 to 70 in my bill !
Answer
Furnace may not be set up right. As in was its input rate checked in both stages, and the blower adjusted properly? There is no way to make it go to second stage right away, 10 minutes in first then second stage is built into the board.
Probably 5 to 10% increase in heating bill between 67 and 70.
Follow-up
You said 10 minutes and the second stage should kick on. When my furnace kicks on it runs for 6 to 7 minutes and it stops, should it be running longer if so should I have someone come out and take a look at it.
Answer
It could be that the CPH is set to 4, or that the furnace is slightly over sized. That it’s not running longer. Of course at mild outdoor temps, it won't run long enough to go to second stage.
What thermostat do you have, and what size house.
Answer
Your house is heating up fast enough that it does not hit the 10 min mark to go to 2nd stage. Will go there on real cold days or if you have a true 2 stage thermostat installed. Look on the circuit board to see if there is a wire attached to W2. If not then you have 1 stage and timed switch over. Higher temp runs it longer and progressively gets the further away areas warmer. If it was going to 2nd stage the fan would blow more heat faster there. With a 2 stage stat it needs to drop more than 1 deg F B4 it switches to 2nd so in mild weather the furnace can probably keep up with the load on 1st stage and you just need to get used to it. High efficiency units supply air at 130*F which is 20* lower than the older units and feels different but you get used to it. 2 stage thermostat needs another wire from stat to furnace installed.
Answer
The Goodman GMH can't be controlled by a 2 stage stat. Goodman made it that only the furnace control board controls the staging. They decided to cash in on the customers that want the comfort of 2 stages, with a low price. But the customers don't know that they don't get the comfort that 2 stages are suppose to provide, because the board is crippled, to make it cheaper. |
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