HVAC Fan vs Furnace


This may sound like a dumb question but hopefully, someone else may have the same one. When Sense identifies my HVAC fan as a Furnace should I leave it tagged that way? We have a gas furnace and I believe that the same fan is used for the AC unit in the summer. Which way do we think it should be tagged to be most correct? Furnace or HVAC fan? :smiley:



since its winter, I’d leave it as the heater fan until the A/C gets used and you can verify that its only the fan… and yes, the blower is the same for A/C & heat…

in heater/furnace mode, there may be other electronics that are running and the signature may be different… also, HVAC systems usually have separate stages for A/C and heat… so even though the fan/blower is the same, it may be in different stages (speeds) that detect different signatures in sense… that supports my suggestion above…




Awesome Thanks for the advice :smiley:



no problem, ask anything… I don’t know everything, but this I know… I have a single stage (compressor) package unit on my roof… and even though the unit only has a single blower and heat/cool have their own fan stage and they can’t be the same because of the way it wires up… the blower has 6 fan speeds on the circuit board… to change fan speed, on my unit, I move the blade connector to the appropriate speed on the circuit board… there is a wire for heat and another for cool… they go on whatever speed is needed… but each can only have 1 (single stage blower), but they can’t be the same… usually the heater is a lower speed, but not always… these are all things dictated by the mechanical designer… I’m one of those too… I am an energy consultant here in CA and I also design HVAC systems for homes… so in my plans, I tell the HVAC contractor which speed each stage gets to make the capacity of the unit proper for the home and duct design…



I initially left mine as Furnace Fan for both my upstairs and downstairs units, since I really use in all 3 modes

  • Heating
  • Air circulation without heating and cooling - 5 min per hour
  • Cooling

Then I put both my forced air furnaces on smartplugs, so the identified fan cycles got merged with the rest of the furnace heating components (igniter, ignition blower).



My Central Heat was discovered this morning. I am happy with the way it is being monitored by Sense. It shows on as soon as the burner ignites, switches to off only when the blower stops. When the burner starts up is shows 31w, then when the blower starts it shows 256w. The only other gas appliance in our home is the water heater. I am looking forward to that being detected. I am also looking forward to the start of A/C season, so Sense can detect that too. Same blower, but of course the condenser is outside.

I also really like the fact that today when Sense identified my Central heat, it included the entire history since January 1st when I first installed Sense.



BTW, when I dig into the energy monitor and zoom in to view the second by second wattage I can see the variable speed blower at work. As suggested by HiTechRedNeck - I think that HVAC will be detected and monitored as a different device, even though the blower is shared.

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I’d stick with the suggestion of leaving it alone for now. When A/C season gets here you can better see what’s going to happen. It is the same air handler fan but in summer it should detect your outdoor unit and you will probably merge them and call it something like “HVAC” since it covers heat and air. I’m afraid if you don’t do something like I’m suggesting with merge and rename that when your a/c outdoor unit it will force the “furnace” fan at the same time and will look like your running both heat and air. What I’m saying only applies if your heat is something other than electric like oil, natural gas or propane. You could just rename it now to “HVAC Fan”.
There is already an entry for this be navigator device page, click name, type, cooling and there is a stock entry for “Fan” there.



I suggest that it may be misleading to think of sense as a system with “binary” detection capabilities (focusing on the blower). I think about the signal intelligence. When my gas burner lights up there is a spike as the igniter lights the gas. Then things go quiet (low current) as the heating element warms up. Then the blower starts. There appear to be six blower ramp up stages in the first two minutes, followed by peak blower. Then, when the burner shuts down, the blower settles into a lower stage for 2 minutes as it cools the heating element. I suggest that that sequence of detected activity is a signature for Central Heating.

The signature for HVAC will have different characteristics. Yes, there is another distinct system starting up (the compressor, but the signals produced by the blower when it engages may be similar, or quite different. Tip of the hat to HiTechRedNeck. Sense is detecting a distinct system called HVAC. We know that the blower is associated with both. Sense could care less.

When AC season starts I might discover that I am full of beans. If so, I’ll admit it here.



When the compressor starts on mine and what I’ve seen in the past is a spike at the beginning of compressor and fan startup for the outdoor unit. They both use capacitors to help with hard starting conditions.
The inside blower is setup different and usually has the ramp up you mention unless it’s a single speed. My new system has this single speed where in heat mode low is used and in cool it uses high. It does t fluctuate except that there is more electricity used when running on high speed. There is also medium but it’s unused.
Sense has detected my heat pump which it originally named furnace. It recognizes any part of the ssytem whether all or part are running as the heat pump.