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Modulating Furnace and Home Automation

MikeW

New Member
I have a Rheem modulating furnace and a modulating thermostat. I would like to use a communicating thermostat and integrate it into my home automation system, but I haven't seen any communicating thermostats which are compatible with a modulating furnace. I can "downgrade" and use my furnace in a non-modulating mode, but I really like the comfort that it produces. Does anybody know of any communicating thermostats that work as a modulating thermostat?

MikeW
 

IVB

Senior Member
IIRC, a modulating furnace is one that automatically changes the gas mix as well as the fan speed to maintain a consistent air-temp.

Does the thermostat have any modulating capabilities, or is that all handled by the furnace?

Or, put another way, does the thermostat just have the basic 5-wire hookup to the furnace, and the furnace has an onboard controller that intelligently determines the right fan speed & gas mix?

I would think all the thermostat has to do is tell the furnace what temp you want and what temp it is, and the furnace would handle all else. Then again, I know nothing about such things and am prone to talking out of turn to begin with.
 

compuguru

Active Member
jlehnert said:
My first question would be....What's a modulating furnace?
A quick google yielded this: http://www.toolbase.org/techinv/techDetail...echnologyID=259

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%.
 

MikeW

New Member
IVB said:
Does the thermostat have any modulating capabilities, or is that all handled by the furnace?

Or, put another way, does the thermostat just have the basic 5-wire hookup to the furnace, and the furnace has an onboard controller that intelligently determines the right fan speed & gas mix?
I will have to investigate a bit more, but I'm pretty sure the thermostat is part of the modulating system. I'll verify this in the next couple of days.

I really want to get my HVAC integrated with my CQC system, but I don't want to give up the modulating feature of my furnace to do so.

MikeW
 

Guy Lavoie

Active Member
A modulating furnace is similar to a servo system, where it varies the heat output and fan speed in order to match the heat loss rate of the house. To do this, it needs a thermostat that can send a signal indicating how far off and at what rate the air temperature is diverging from the setpoint. These systems are known for their high effeciency due to avoiding cycling, and better comfort. Unless you can get an equivalent thermostat that also communicates, I would not mess with it.
 
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