Make a Shop Water Heater out of an old Humidifier

On cold days I really want a warm water source in my shop. I don't need a whole tank full 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.

I've used a hot plate, crock-pot, 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. I had to pour the hot water into another container, maybe  mix in 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 that had a water heater built in. I just added an old spray hose to the humidifier, and now I have warm water whenever I need it.

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 in the reservoir.

Every winter, someone gives me at least one non-working humidifier. Until now, they have all been those small ultrasonic humidifiers designed to condition the air in one room. They work great for a year or two, then break. They are simple designs, just a piezo-mister and a fan, 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 the donated machines.

I even did a video about some of the goodies you can find inside a typical unit. A magnetic reed switch with floating magnet is perhaps the most rare part. These are good for water sensors, movement sensors etc. The 110v switches and potentiometers are also handy to save. There is the usual assortment of fans, LEDs, transistors and MOSFETS to scavenge. And many of these components are on their own tiny PCBs complete with a wiring harness and JST connectors. This makes them easy to install in your own projects.



By now I have a large collection of the typical components, so I was looking for something else I could do with a broken humidifier besides part it out. I toyed with the idea of a pet watering station or an irrigation system. The self-regulating water flow mechanism made old humidifiers attractive for such projects.

Then this winter, someone donated a deluxe version that turned my ideation in a completely new direction. This thing had all kinds of controls. A fancy display allowed you to select the desired humidity level, the fan speed and the option to heat the water before misting. I took the machine apart to see what was broken. It had failed at the typical point, an overheated MOSFET just like the cheap machines. But the driver circuit was separate from the other circuits, so everything else still worked.

I was impressed with the overall quality of the build. It was probably why this machine had lasted eight 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. Before it melted, the MOSFET was rated for 94v, so that piezo could pump out a good bit of mist. There was also a temperature and humidity sensor that fed back onto a solid control board.

This is the top view of the humidifier's base. The blue plastic water-reservoir sits on top of it.

This is the bottom of the humidifier's base. Normally I scavenge all the tiny breakout boards and sensors. But this time I left everything in place except for the piezo and driver. All of the other parts still worked.

Burned out, fried, broken and non-working. This is the driver board for the piezo misting disc. Like a lot of humidifiers, it was the point of failure. Without the electrical pulses from this board, the piezo did not move or produce mist. When I saw the 94v marking I decided not to even try to repair it. And the board had gotten so hot the PCB had warped and separated. 

The most interesting part, at least to me, was the heating element. The heater uses 110VAC and looks like a typical ceramic cartridge heater, although I didn't unwrap it to check. 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.

The heating element appears to be a standard ceramic resistor style running on 110v. A metal sleeve covers a silicone tube that connects with the base of the humidifier with a pair of angled rubber hoses. The heater seems to stay on as long as there is water in the base, but the temperature of the water never goes above 120F

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.

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.

The water in the base of the humidifier gets heated to about 120F, the temperature of a typical household hot water spigot. It take about 15 minutes at normal room temperature, longer when it's 40F in the shop. After an hour or two, the water in the blue plastic reservoir gets heated to about 90F.

I knew the heating element would be good for some type of fun new project, so I kept the humidifier intact while I ruminated on how best to use it. I thought about scavenging 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 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 holding pan into a hose and nozzle. That seemed simple enough, and it was, but I did it in the most difficult way possible.

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. It seemed safe.

The piezo disc that creates the mist did not work anymore because it's driver-board was burned out. When I removed it I had an aaccess hole, and when I removed the frame I had an even bigger hole for attaching the sprayer hose.

After removing the piezo mister, I had a nice hole to connect to the sprayer hose. Unfortunately, the hole was so big that none of my normal plumbing fittings worked. I had to make a custom gasket and use several adapters to get everything hooked up. If I did it all again I would leave the piezo disc in place and drill a "normal" sized hole so I could attach the spray-hose directly to the base.

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 scratch-built sci-fi models. So I had a bunch of old fittings of various sizes to work with. It still took me an hour to find a combination of fittings, adaptors and eventually, custom-made gaskets that would work with the oversized hole. Yes, it works fine... but I would do it very differently next time.

I cut a notch out of the base's side wall for the hose to run through, then reattached the base and filled the reservoir. There were no leaks, so I plugged it in and waited for the water to heat up. It worked. I had warm water on demand. I was happy.

Now I have a water heater and spray hose for the shop. I can clean things with warm water, spray off the sanding dust with warm water, or just wash my hands... with warm water.

Even though it worked almost exactly like I had planned, there are things I would improve next time. Drilling a "normal" 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.

There isn't much pressure, the water does spray but it's not going to knock anything off. You aren't going to use the scrubbing action of a typical high pressure sprayer to clean dried eggs off a breakfast plate for example.

I thought the reservoir was huge, but it's not actually a lot of 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 the sprayer. I use the sprayer a lot, but sometimes it would be nice to have a continuous drip on a sanding/polishing project.

The heater does shut off when the water tank is emptied. But I would still feel better if I had an automated shutdown system. Maybe turn it off after midnight, or if no motion is detected after an hour. And a 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 actually. But I probably won't connect a water and temperature sensor to an alarm.

Yes there are better solutions to adding warm water to your shop. There are nice portable water heaters for less than $150 USD (affiliate link) which undoubtedly work better. But for free, using nothing but donated and scavenged parts, this is one of my most successful and functional hacks.

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