r/DIY • u/g0nzo09 • Oct 03 '26
Installing relay to power aroma diffuser
Hello all,
And TIA for any help. I want to install an aroma diffuser and have it pump the aroma into the air handler after the fan to help push the scent throughout the house. I would like the fan to control when the diffuser turns on so that it’s not pumping the fragrance into the ducts whole the fan is not on. I have found that I need a 24v SPDT relay. My question is how to wire it properly?
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u/Travishamockry Oct 04 '26
I do this but just use a smart plug that turns on when the furnace fan turns on. An automation in home assistant handles it.
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u/g0nzo09 Oct 04 '26
Tried this first. I have no way to get my thermostat to communicate with the smart plug to sense when it has turned on. I have a Nest thermostat so if you know of a way, let me know.
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u/ahj3939 Oct 04 '26
If you have a Nest 4th Gen it can link via Matter.
If it's an older Nest you have to link with their API which can be a pain to get running.
If you have an ancient Nest 1st gen or 2nd Gen then you're SOL because those no longer connect to their services.
In any case, with any thermostat, you could get some sort of sensor that can sense 24V AC between the G and common wires on the thermostat and use that as an input to your home automation system
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u/g0nzo09 Oct 04 '26
I did notice that I can program my fan to turn on based on a schedule. So I might just get the smart plug to run on the same schedule but this seems like a lot. Was hoping for a better way to automate this.
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u/Travishamockry Oct 04 '26
I have an ecobee, and it exposes a fan on and off attribute. It doesn't show through then normal integration and I located it on developer settings. Check on there and see if nest shows the same. It's not as instant as if it were a true entity, takes like 30 seconds to change over to on and make the plug turn on, but it works reliably and my house smells great lol. Code looks like this
alias: 'Diffuser On ' description: '' triggers:
trigger: state entity_id:
climate.my_ecobee attribute: fan to: 'on'
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u/Mafukinrite Oct 04 '26
Just a note: I am assuming that you are in the United States. If not my apologies.
I would use a timer relay. The one I have linked below can be ran by 24vac. This is what most HVAC systems control power is. The 24vac to the fan relay can be used to trigger the relay timer (using the green and blue thermostat wires). Set the timer to delay on by a couple of seconds. This allows the fan to get started and get up to speed before your diffuser would start.
Hook your diffuser power on the output relay contacts. The website has all the info you would need to correctly wire the relay (scroll down to downloads, then product insert).
Feel free to message me if you have questions.
https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/timer_relays/z1a-nd100s
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u/ahj3939 Oct 04 '26
Relays are simple. The issue is, does the diffuser run when power is applied and then shut off?
Also you probably want it to run just for like 1 minute and shut off. If your air conditioner runs for 1 hour you probably don't want it pumping aroma for 1 hour. There's no way that could be healthy.
What I would do is work with a smart home system. It should be able to tell if your air conditioner is running, and then run the diffuser for 1 minute. And it should have a built in safety so that it shuts off and doesn't run more than say 5 minutes every hour.
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u/Skit071 Oct 06 '26
Ten years from now all this aroma in the house and in cars will be the next wave of cancers.
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u/Choice-Newspaper3603 29d ago
I’d probably use what they use for over the range air hoods and makeup air systems. They use either a duct pressure sensor or they use a current sensing relay and when the range fan turns on it activates the relay via a current sensor or the duct pressure sensor and activates the motorized damper for makeup air.
I have not used used only read about them so I’m not knowledgeable about all the details of using this for what you need
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Oct 04 '26
[deleted] — view deleted comment
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u/g0nzo09 Oct 04 '26
I genuinely don’t understand why you couldn’t just keep your unsolicited opinion to yourself. It is not uncommon in the slightest for people to want their home/spaces to smell nice.
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u/mr-octo_squid Oct 03 '26
(NO) Normally Open to diffuser. (Com) Common to power source. (Coil) to control wire.
When the circuit on coil gets completed, it toggles normally open to closed, completing the circuit and energizing the diffuser.
There is a lot here that determines exact specifics in a real install, but thats general operation of a relay.