Introduction: Make a Water Heater From a Humidifier

On cold days I really wanted a source of warm water in my shop. I don't need a large tankful, and I don't need it every day. But on cold days it would be nice to wash my hands with warm water or keep my fingers from freezing when I'm doing wet-sanding or cleaning.

In the past I've used a hot plate, a crock-pot, an electric kettle and a coffee maker to heat water. They all heat up the water and it's nice to have a pot of warm water to dip things in. But I always found them inconvenient because there is no dispensing mechanism. The water was often too hot to be used immediately and safely. I had to pour the hot water into another container, maybe mix in some cool water, then dip the objects or my hands into the water. That's too much trouble. I wanted a hose and spigot so I could just spray down the dust and wash my hands easily.

I finally found a solution when someone "donated" their broken home humidifier. This humidifier (marketed under several brand names) has all the bells and whistles. It has a humidity and temperature sensor that allows you to set the fan and misting levels. And more importantly to me, it has a heating element that warms the water in the base and reservoir to a safe temperature.

I just added an old spray hose to the humidifier, and now I have warm water whenever I need it.


You will need:

  • An old humidifier that heats the water. Not all humidifiers heat the water before turning it into mist.
  • A hose and spigot along with the plumbing fittings to attach it.
  • Screw drivers.
  • Drill and bit (preferably a step bit.
  • A multi-meter to test and troubleshoot the electronics.

Your humidifier will probably be different, so the exact configurations and fittings will vary from mine.

Step 1: Could I Fix It?

I have scavenged parts from a lot of humidifiers. Every winter I get at least one broken humidifier given to me. I keep thinking that eventually I will have enough spare parts to rebuild or repair one, but so far they have all been too different and repairing them would be more expensive than buying a new one.

Except for this one, they have all been small ultrasonic humidifiers designed to condition the air in a single room. They work great for a year or two, then break. They are simple designs, just a piezo-mister and a fan. They are so cheap it's more convenient to replace them than repair them. Despite their simplicity these units have lots of components that are worth scavenging, so I continue to happily accept and salvage their components.

I even did a video (attached) showing some of the goodies you can find inside a typical unit.

A magnetic reed switch with floating magnet is perhaps the most rare part. It's used as an automatic shut-off switch to power down the unit when the water falls below a certain level. These are good for creating water sensors (of course), but they can also function as movement sensors, puzzle boxes etc. I recently had to hack one in a waterproofed flashlight.

The 110v switches and potentiometers are also handy to save. There is also the usual assortment of fans, LEDs, transistors and MOSFETS to scavenge. And many of these components are on their own tiny PCBs that come complete with a wiring harness and JST connectors. This makes them easy to re-use in my own projects. By now I have a large collection of all the typical components so this time I was looking for something else I could do with a broken humidifier besides part it out.

I took the fancy, newly acquired humidifier apart to see what was broken. It had failed at the typical point, an overheated MOSFET on the driver board for the piezo mister. Before it melted, the MOSFET was rated for 94v, so that piezo could pump out a good bit of mist. It was a much more expensive humidifier, but it failed just like the cheap machines. Luckily, the driver circuit was on its own PCB, separate from the other circuits, so everything else still worked.

I was impressed with the overall quality of the machine's build. It was probably why this machine had lasted several years instead of the usual two or three. It had a big 48v squirrel-cage fan instead of the wimpy 12v like on cheaper models. There was also a temperature and humidity sensor that fed back onto a solid control board.

The most interesting part of this machine, at least to me, was the heating element. It was the first humidifier I had seen with a heating element. The heater looks like a typical ceramic cartridge heater, although I didn't unwrap it to check. It uses 110VAC, so I was sure to be careful when tinkering with it. The heating element is attached to a metal sleeve that surrounds a silicone tube. The tube attaches to a pair of rubber angles which attach to the body of the humidifier. Cool water flows into the lower end of the heating tube, gets warmed up and rises to the higher end of the tube to create a natural circulation pattern.

There doesn't appear to be a thermistor on the heater itself, but the temperature and humidity sensor are located nearby. It seems like the heater is either always on or always off and it is not part of a feedback control system. There may be a shutdown programmed if the temperature sensor reaches a certain level, but it appears that the heating element was designed to never go above a certain temperature no matter how long it was running.

The water level sensor does, however, shut off the heater, mister and fan when all the water has evaporated and the tank is empty. The heater will warm the water to around 120F in about 20 minutes, the same temperature as my kitchen sink's hot water. Within an hour or two, the water in the reservoir tank is also heated to around 90F. (Of course it takes longer when the shop is 40F instead of 70F) That's a perfect temperature to keep my fingers warm when I'm wet sanding or cleaning. No chance of getting burned and no need to mix in cool water. A little extra insulation and the water might heat up even quicker.

I knew the heating element would be good for some type of fun new project, so I kept the humidifier and its circuitry intact while I ruminated on how best to use it. I thought about scavenging just the heating tube and hacking it onto an old pot. If I also put a spigot into the pot, I could have a miniature hot water heater. With a little drilling and sawing and soldering I could make this work.

Then I realized that I could just use the entire humidifier. So much simpler. It already had everything I needed, all the electronics and controls and safety features plus a portable water tank. All I had to do was get the water from the misting chamber into a hose and nozzle.

That seemed simple enough, and it was. But I did it in the most difficult way possible. I thought, since the driver board for the piezo mister was completely fried, I could just remove the piezo disc and use the resulting hole to connect a hose to the humidifier.

Sounded easy, but before I started I carefully tested all the electronics and feedback systems. The heater, fan and sensors all still worked after I removed the piezo and driver board from the loop. More importantly, the water-level sensor and auto-shutoff system still worked. So it would still be safe to use.

Step 2: Adding the Hose and Spigot

Now all I had to do was connect a scavenged spray hose to the piezo's mounting hole. I keep lots of junk plumbing parts that other people would throw away. I use them for my Steampunk crafts and kit-bash sci-fi models. So I had a bunch of old fittings of various sizes to work with. I could have gone to the hardware store and bought the correct fittings, but where's the challenge in that?

I thought about using a traditional hose spigot and running it through the bottom wall of the reservoir. But It would sit so close the the shelf surface that I would have to elevate it or extend it over the edge of the shelf to get a pot or my hands under the water stream.

I also thought about running a hose or pipe to a remote spigot. But that would make it a lot less portable. I wanted something I could move close to whatever workstation I was using.

I finally settled on an old sink spray hose. It still had the spray-head, the hose and the fittings. All I would need was a way to connect it to that empty piezo hose. It sounded simple.

However. it took me an hour to find a combination of fittings, adaptors and eventually, a custom-made gasket that worked. None of my standard plumbing fittings matched up with the oversized hole from the piezo. Eventually I cut a custom gasket out of a piece of PVC plate, drilled a hole in it to accept standard plumbing fittings, and used a compression ring to attach the spray hose to the gasket. Then I used silicone to seal the gasket into the hole.

(Yes, it works fine... but I would do it very differently next time. I suggest leaving the piezo safely in place. Do not remove it like I did. Instead, use a step bit to drill a standard plumbing sized hole in the bottom of the misting chamber. Then just use regular plumbing fittings to attach into the new hole. No custom gaskets or silicone caulk needed. Also, a quick trip to the hardware store to buy parts designed to work with each other would probably be a good idea. I wanted to use only free scavenged parts, which caused me more trouble than the goal was worth. )

I cut a notch out of the humidifier's side-wall and ran the flexible spray-hose through the notch. Now the humidifier could sit flat on a shelf or table. The hose was long enough to reach

Finally, I reattached the base-plate and filled the reservoir. I waited for an hour and there were no leaks around the custom gasket or my plumbing hacks. So I plugged it in and waited for the water to heat up.

It worked.

I had warm water on demand and I could carry the water heater to whatever workstation I needed. The hose dispensed a gentle spray of water, great for hand washing, dust suppression or cooling. It worked better than I had really anticipated.

I was happy.

Step 3: Conclusion

Ahhh, warm water wherever and whenever I need it. A small luxury, but it makes shop life so much better. It might even extend the working season by a couple of months. Even though it worked almost exactly like I had planned, there are things I would improve next time.

Drilling a "normal plumbing" sized hole through the case while keeping the sealed piezo in place would have been so much simpler. Just use one connector designed for the newly drilled hole and skip all the adapters and flanges and gaskets.

The water is gravity fed so there isn't much pressure. The water does spray but it's not going to knock the dirt off anything by itself. You aren't going to blast dried eggs off a breakfast plate for example.

I thought the reservoir was huge, but it actually holds a very small amount water. You can empty the reservoir fairly quickly by cleaning just a few projects. Luckily, it's easy to refill.

I wish I had designed in a "drip hose" as well, maybe with a splitter for dual use with the sprayer. I use the sprayer a lot, but sometimes it would be nice to have a continuous drip of warm water on a sanding or polishing project.

The heater does shut off when the water tank is emptied. But I would still feel better if it had an automated shutdown system. Maybe turn it off after midnight, or if no motion is detected after an hour.

An equal worry is that I will turn off the heater but forget to empty the reservoir and the water will freeze overnight and destroy the entire machine. That seems more likely.

And yes, I know there are better solutions to adding warm water to your shop. There are nice portable water heaters for less than $150 USD. They undoubtedly work better, but I don't have running water in my shop (yet) so this was a good solution.

Overall, it was a success. It was completely free, used nothing but donated and scavenged parts and was one of the simplest, yet most successful and functional hacks I've ever done.

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Second Prize in the
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