Based on this site:


It looks like nest recently added support for multi-speed fan control for some furnaces.

I'm looking to buy a new furnace (mine is old and past its life), but really like using the nest thermostat. It's the first thermostat I've ever used that I actually like. I would like to be able to control as much of the new furnace's features with the nest as possible.

My understanding is that sticking with Nest means I can't use "modulating" or "variable speed" furnaces. However, I think I should be ok with a 2 stage multi speed furnace. 95% efficiency is obviously not as ideal as 98%, but I think I can live with it if it comes with substantial UX benefits.

However, I don't seem (for the life of me) to be able to find any info on what multi-speed furnaces are actually compatible with nest control. In other words, what furnace models use 2 thermostat wires for fan speed control?

Do any of you guys have an info?

  • Shopping questions are off-topic; however, if you have specific furnace models in mind but can't find info on whether they'll be compatible with two stage fan control, we can help with that. – ThreePhaseEel Dec 18 '16 at 3:13
  • Ok... The website for the Trane XL95 says it has a 4 speed blower motor. Do you know if this is compatible with the nest multispeed fan control? Will the nest be able to independently set the fan speed? – Scott Wisniewski Dec 18 '16 at 3:17
  • Try asking Nest what to look for to determine compatibility. They should have documentation which covers that. – keshlam Dec 18 '16 at 3:21
  • They do, it's in the link in the OP. It says that it can control multispeed fans if the system has 2 fan wires instead of one. I can't find any info on what furnaces support that, and which ones don't. – Scott Wisniewski Dec 18 '16 at 3:23
  • Additionally just because a furnace has a 4-speed blower motor it doesn't mean that 4 speeds are available at the thermostat. Most furnaces have multi speed blower motors that are installer configurable via jumpers. – Tyson Dec 18 '16 at 3:41

I am familiar with two basic control schemes for residential units: (1) Relay logic (old school 24vac on/off), and (2) Communicating (direct digital control via serial communication).

I believe what you seek is any multi-stage furnace that is not exclusively a communicating furnace. This type of furnace will have a W1 and a W2 for stage 1 and stage 2 heat, and might control the blower speed automatically or it might have multiple discrete fan speed selections labeled G1, G2, etc, which the multi-stage Nest should handle.

I say this based on a brief review of the literature online and I have never actually installed one of the multi-stage Nest thermostats.

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