Hot tub temperature monitor

I've been using a sonoff temperature sensor floating in an iPhone bag in my hot tub for a while. It works pretty well all things considered. I recently installed some Ecowitt sensors for another purpose and realized they make a nice temperature sensor for pools and hot tubs. There's a transmitter that mounts on the outside of the hot tub with a 10m wired probe.

Here's my question: what's the best way to make sure the probe stays put and doesn't swirl around the hot tub when the jets come on? I thought maybe I would glue it to the side of the tub, but if so, what's the best kind of glue? Some sort of marine epoxy perhaps? Anyone else have any less permanent ideas?

How about a suction cup and affix the probe to that?

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I don't have a hot tub myself... but does the water get cycled through a common point internally? So a common point where the water is heated / filtered? Could you use the inlet / outlet for that point as a point to measure the temperature, with an appropriate allowance for increased / decreased temperature depending on where the sensor is located?

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Yes. Right now it's wire tied to the filter holder. That may be sufficient, we'll see.

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That's an excellent suggestion!

Fish tank suction cup tube holder. Brilliant!

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Think of all the cool additional HE apps we would have if you DID have one! I use the sensor more to check the status of the tub than anything else. Sometimes when the generator kicks in it trips the hot tub circuit breakers. Nothing like opening your hot tub a few days later to discover the water has not been circulating. It's pretty gross.

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I’ve seen pvc thermos wells that I plan on cutting into the plumbing of our hot tub once the warranty is up.

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A braver man than I.

If that's not a reason to get one, I don't know what is.... :slight_smile:

The only experience I can offer you is in home brew, so can only recommend a temperature probe used when boiling grain for producing beer. Not sure that is what you want in a hot tub.... Though maybe an extension of @potts.mike 's suggestion...

The ecowitt works great... there was actually another post on a related topic and I suggested my sonoff floating bag solution a while ago. It does work but this is cleaner.

Screen Shot 2021-11-04 at 11.09.05 AM


Silicone adhesive.
It is completely waterproof and can easily be removed, later.
Surfaces need to be dry when applying, and you'll want to wait 24-48 hours for it to cure before you get it wet.

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What about the wire? I guess it has to go up over the side and down into the tub. What about possible damage from people, or the hot tub cover?

I have a hot tub at a rental property we own, and I've been toying around with the idea of monitoring its status. I'm not as concerned about the temperature as I am about it not running at all, which means the circulation pump and ozone generator wouldn't be working.

For temp monitoring, I think I'd look into a way of getting the probe directly into the water flow somehow. Maybe by inserting a T with a threaded plug into one of the lines inside the equipment area.

Yeah same with me. I need to know if the thing has stopped running, because it will very quickly turn into an oversized petri dish. The wire is a concern. It does run up the side of the tub, over the edge, under the cover, and down. Which is why I didn't want to use 5200 to attach the probe to the tub. But there are only two of us who use it (though it is a 7-person tub) so we can be gentle. If it lasts a few years and fails, it's only $30 for the unit. And I bought two!

A probe in the plumbing, so to speak, would be a good idea. I'm just not really into drilling into the innards. This method is low impact, completely reversible, and cheap.

saw this post and wanted to add my experience - I have an ultrasonic tank that I designed and did a lot of work with temp sensors as well as bulkhead mounts and marine grade epoxy.
That Epoxy sure is permanent :slight_smile: Where you mount your sensor is critical. I was advertising .1 degree accuracy and ultimately learned about circulation and temp differences in liquids. I ended up using a bulkhead sensor than ran the wire feed over to an external controller for digital display. This allows me the ability to swap the controller (US vs EU) depending on the customer.
Because of the volume of liquid, the location of the measurement is a big deal - if you measure at the inlet vs the drain could be a 30degree swing! I realize this topic is closed, and I didn't read all of it but I want to write a huge paper. I wont tho.

What sensor are you using? Couldn't find anything but fixed temp sensors on the Hewitt web site.

Closed only because the immediate question was how to secure the sensor in the hot tub, and the fish tank tube suction cup seems like the thing!

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Damn. Sorry. My bad. Ecowitt. Not Hewitt.

They make two versions. One has a rod, one has a cable. Both require a wifi gateway but @sburke781's integration is not cloud based.

Thanks, this looks interesting. Is the probe cable permanently attached? If not I think I'd drill a small hole in the filter compartment above the water level and use a rubber grommet and have the wire end up inside the hot tub's equipment compartment.

But in my case I will be dealing with renters, so I wouldn't want an exposed wire. If it was just me and the wife, as you say we could just be careful.

"Permanently attached" is relative. It is not "user changeable" but there are screws! The threads on the post are for a mounting bracket. The probe itself is not really easy to mount other than with an adhesive.