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I have an Ecobee 3 and a Keeprite two-stage gas furnace.

The furnace is currently configured to control its own staging system but I'm curious what would be the advantage of reconfiguring to have the Ecobee control the two stage system. Are there any obvious big tradeoffs?

The relevant facts I can think of are:

  • Keeprite R&D knows more about its manufactured furnace performance profile than Ecobee
  • Ecobee has sensors across the house and knows about incoming weather systems and upcoming heating requirement changes so it should theoretically be able to do a better job controlling the overall system
  • I can't find evidence of Ecobee being this smart
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Operation with better feedback from the thermostat should always give performance that is as good or better than operation without as much feedback. The obvious trade-off is that installing more stages of control may mean running extra wire which may not be easy to do.

If you have a two stage Ecobee3 and you can connect it to the furnace and set the furnace for two stage control, then that should be an improvement over the furnace controlling its own staging, which is usually just a timer that runs the furnace at stage 1 for awhile and then switches to stage 2 if that does not satisfy demand.

I do not know exactly which Keeprite model you have, but the self-control scheme for a single stage thermostat signal is probably similar no matter the model. Here is an excerpt from the Keeprite G9MXT installation guide:

For single_stage thermostats, connect thermostat W to W/W1 at furnace control terminal block. (See Figure 7) For single_stage thermostats, the control will operate for 12 minutes on low heat, then switch to high heat if heat call remains. Setup switch (TT) must be in the factory_shipped OFF position. See Figure 7 and Figure 15 for setup switch information. If a two_stage heating thermostat is to be used, move setup switch (TT) to ON position before starting furnace. This overrides built_in control process for selecting high and low fire and allows the two_stage thermostat to select gas heating modes. The W2 from thermostat must be connected to W2 on control terminal block.

The ultimate in precise control is a digital communicating thermostat if your furnace has that capability.

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The Ecobee knows how far you are away from your setpoint. ie If you set the temperature up 3 degrees C - that is a large jump so it will kick in to stage 2 right away and then later on when it is getting close ( that value you can set depending on your taste, i use 1.7) it switches to stage 1. This allows the warm air time to slowly warm up the walls so that when the thermostat shuts the furnace down the house temp is stable - If you had use stage 2 the whole time - the walls have not caught up with the room temp - so the temp drops and the furnace will cycle on - not as efficient or as comfortable.

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