400M

With that level of guitar, I would recommend investing a bit more and look into humidifying the room your guitars are in or humidifying your whole house. That way, you can leave your guitar out on a stand or hanging on the wall, and you get the added benefit of making your house much more comfortable. My house is \~1200 sq ft, and [this humidifier](https://www.homedepot.com/p/AIRCARE-VALIANT-Gal-Cool-Mist-Evaporative-Whole-House-Humidifier-for-4-000-sq-ft-Brushed-Nickel-HD1409/204364015) is capable of keeping the whole house at 45% (though I do need to fill it more often in the winter months). You would fill it much less often if you're just keeping a single room humidified. The other thing to look into is a [humidifier that plug into your furnace](https://www.homedepot.com/p/AprilAire-Model-400-m-Water-Saver-17-Gal-for-up-to-5-000-sq-ft-Whole-House-Evaporative-Humidifier-With-Manual-Control-400M/312148211). These are great because, once the initial water line is run and the humidifier is installed, you don't have to worry about refilling. It's literally a set it and forget it solution.

Regardless of where you mount it, the evaporated moisture will have to pass through the return and over the filter. You can't avoid that and its perfectly fine to do. Id recommend an aprilaire 400m. For that model it fills a tray and has an absorbent pad that wicks up the water in the tray. As the water evaporates it will refill the tray. It uses a lot less water than a constant flow model. They tend to work better with heat pumps that have a lower temperature output than furnaces. The water in the tray and on the pad is heated over time and evaporates better than a constant flow model as the water is usually cold.

I have this whole-house unit installed in my forced air furnace: [https://www.aprilaire.com/whole-house-products/humidifier/model-400](https://www.aprilaire.com/whole-house-products/humidifier/model-400) In 2015 it cost me $816.50 to have it installed (I'm in Pennsylvania) - including parts and labor. So maybe estimate $1100 today. We turn it on with a fresh filter, usually in December, and it runs on automatic through the winter. I should change out the filter at least once in the winter but I usually don't. We turn it off in March/April.

Just get an aprilaire 400. They work fine for that size house.

My Aprilaire 400 works just fine with cold water. My windows sweat if it's set too high.

I have Mitsubishi P series as well. I put an AprilAire 400 on my return duct. You can locate it on the front (narrow) side of your return duct. Feed it from the close by supply side. Only use your thermostat for temp sensing not return. This is configurable in function settings. Works great. Steam uses too much electricity IMO.