HS110 use on water heater

Hi All,

So Sense continues to find things 1+ months in after install which is awesome! I “think” I have a batch of HS110s coming in. Sense has not found my gas water heater yet and hoping the HS110 can be used. Since it’s gas, will this water heater work with the HS110? It is a newer (~5 year old) AO Smith 50gal? I can get model # if needed. Not sure where to find max wattage on unit. I bought new a few years ago so I have owners manual somewhere.

Any help appreciated!


Not sure there’s anything electrical on a tank-based gas water heater to plug the HS110 into ? I had a similar tank-style gas heater until recently and I did have my recirc pump on an HS110. Maybe you have an electronic controller and electronic ignition ? If that or recirc pump, you’ll see the energy used by that “component” of your water heater, but not the actually heating energy.

ps: Now I use the same HS110 on my Rinnai tankless heater that has electronic controls and recirc pump built into it.

@kevin1 there are controls as well as an exhaust blower motor that plugs into the wall. My assumption is the HS110 would be able to show me at least electricity consumption. My concern is if the HS110 can handle the draw thru it however I’m not sure what the draw could be or where to look.

I also have a natural gas-powered water heater. Five weeks ago, I put the electrical portion of this unit on an HS110 and it has worked fine since then. Here is a sample output from this morning.

Please note that the wattage is well within the capacity of an HS110. Not visible in the image is a 1 watt draw continuously when idle. This is unusual for a fan, so there must be something else going on inside the water heater.

I used the Kasa app to schedule this HS110 “off” during the hours I am normally asleep. The minuscule energy savings from that schedule adjustment will never pay for the HS110, but is better than nothing since I already bought the hardware.

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My guess is that a blower, controller and igniter will not exceed the limits of the HS110. I have two furnaces on HS110’s, and they don’t really ever go over 600W, except for the startup spike.

108w is not huge but it’s interesting to ponder the amount of water you can heat using a good air-source heat pump, with say a 3.7UEF ==> 400 watts (ish)

If you start at 60F and raise to 120F I get near 3 gallons/hr.

Seems like a safe bet to use it then. As hard as these things are to find, I’d hate to burn one up or ruin my water heater. I am currently awaiting arrive of 2 HS110s however just a bit skeptical what I get won’t be HS100s.

Appreciate the info and feedback!

@jefflayman due to COVID-19, my utility company decided to delay implementation of summer peak hours for usage. As my multiple ecobees control the A/C, I’ve been trying to figure out a simple way to not run the water heater at that time so I thought this would work as well for that. I do like the idea of off time during the night as well.


As a general rule, if a device plug in to a 120V 15A outlet then the maximum amps it’s going to draw is not going to kill an HS110. That said, you should not push an HS110 (or 15A circuit) close to it’s max current/power.

I wouldn’t imagine that the modest usage of your tank blower is going to be something to get overly concerned by. If you had an electric tank, and particularly an electric-resistive element tank, then you would want to track that usage and avoid peak utility hours.

Did you check your peak hour usage? I’m guessing AC or other high-usage devices would eclipse anything the tank blower is consuming.

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@ixu when blower in use, doesn’t pull many watts as you note certainty compared to A/C however any usage I prevent at peak hours, only saves me $. Using ecobee schedules and HS110s on washer and hot water heater will help wife, teenager and younger kids not operate non-essential devices during 2-7pm. :grin: guess I need to check if dishwasher is wired or plug in. We don’t have a lot of high wattage pull devices but limiting vs full use during that time will help.

Is the tank plumbed with a thermostatic mixing valve? If you set the thermostat high and get it to temperature before 2pm you should reduce the chance of the tank activating for those 5 hours.

Ideally you would turn the thermostat down to say 122F at 2pm and back up to 140+ after 7pm!

Sense + HS110 would help you confirm the efficacy of course.

Signs on bathroom doors? Locks?

Good luck.

@ixu Not sure on water heater mixing but doubt it, just run of mill natural gas water heater.

Scheduling/planning more about making sure family is cost conscious, I’d rather spend $ on family trips, going out, etc that everyone can enjoy vs just spending it on boring electric bill. Probably compared to other homes this size, we don’t have a lot of energy hogs which is helpful but the last couple years I’ve noticed our budget pay amount continues to increase and bought Sense primarily to make sure there isn’t something I’m not aware of burning electricity but also to curb the yearly increase.

Since we are home 24/7 now, simple things like not running our high pull stuff during peak cost hours will go a long way on savings. On hot days, the A/C will definitely run during that time which is fine (I hate being hot) but I’ve scheduled to cool house down to a much cooler temp prior to peak rate time so it runs less during peak rate hours. That is more of how I’ve been during planning. Wife normally does laundry in morning so having on washer will help keep teenager on schedule to do her laundry morning or afternoon vs peak…If washer isn’t powered during peak time which isn’t real high energy hog, the dryer will not likely be needed during peak rate hours…stuff like that.

Thermostatic mixing is quite common and necessary by code in some places I believe, especially if you have a gas powered hot water tank. Basically, it’s safer to heat water well above 120F to kill bacteria (things like Legionella) but then the water is dangerously hot to use, especially with small kids around.

You could test whether you have the automatic mixing going on, which blends the tank hot water with cold water to bring the temperature down, and that’s what is fed to your hot faucets.
Cautiously (when no kids or unaware adults are around using water) make a note of what the tank thermostat is set to and then turn it up to near maximum … the gas should turn on immediately and heat the water to that setting. This is not the thermostatic mixing temperature, which is normally set (fixed) to 120F or thereabouts. Wait until the tank switches off and then go around to all of your hot water faucets and test (cautiously) whether the water temperature has increased significantly. Be careful, the water could be scolding hot. If so, you probably don’t have the automatic mixing anywhere so you should turn the tank thermostat down again to where it was at a safe temperature.

This is essentially like your pre-peak super cooling with the AC. The higher the tank temperature the less likely it will turn on during the peak period. That said, if it does turn on because a lot of hot water gets used it may run a little longer.

I’m suggesting all this more to explain how the system may work rather than exactly what to do. If you understand technically how the water is supplied then you can make judgement calls as issues arise. This matches what you are doing with the AC.

Personally I would leave the water system alone and write off the modest energy debt and focus on optimizing your AC scheme. I’m guessing you have something like 1 minute of AC “on” equals 30 minutes of hot water blower “on” in terms of power use. That’s something you can quantify in Sense of course.

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A natural gas-fired water heater on a Kasa HS-110 monitor was recently mentioned at Sense Saves (Again!) In that post, @ac.mackenzie11 explained yesterday that his model uses 1W when idle and approx 155W when the heater is running. I repeat that statistic here since it seems relevant to the above discussion.

I recently noticed something about my setup. I had known that the fan inside the unit continues to blow for a little while after the flame stops. The plumber who installed my water heater explained that manufacturers cause their units to do this on purpose. It exhausts any fumes remaining in the vent stack so that moist, acidic vapors don’t later condense and corrode things. What I just noticed is that this behavior is visible as a plateau at the tail of the Sense graph if you zoom all the way in:

This brings me to a potential disadvantage of creating a schedule for the HS-110 serving a gas-fired water heater, as I have done. The danger is that the “off” signal could come while the unit is in operation (ie, not idle). If so, safety circuits would surely close the gas valve so the flame would die, but the extra seconds of fan operation at the end of the cycle would not occur. While this happening once or twice should not be a problem, repeated instances could lead to the corrosion issue that my plumber warned me about.

I am curious about the experience of this thread’s original poster. @norenlaw, how is your setup working after the first month? You seemed interested in creating a detailed schedule, so the above comment may apply to you. In my case, I feel pretty safe with my schedule since my family typically showers in the morning rather than before bed.

@jefflayman not set up a schedule yet. So far based on water heater energy usage so low, to someone’s point earlier there is no real point. So far, HS110 just to monitor usage.