Guns and relative humidity

[Merc]

I’ve always thought 40% was the generally accepted relative humidity level that is moist enough to keep the wood rifle stocks from shrinking and cracking but dry enough to discourage rust.

I have two cheap hygrometers that I don’t trust. One says the RH in my house is 21% and the other says 30%. I have my humidistat set at 40% RH. So, I went looking for a Bacharach Sling Psycrometer and bought one on eBay. It arrived today. It’s a very simple instrument that uses two thermometers to accurately measure RH. It tells me that the RH in my furnace room where the gun safe is located is 41%.

[jjrothWA]

May I suggest that you keep a bottle of water in that room at the ambient temperature, and use an ey dropper for wetting the "wet bulb cloth."

The should give a more consistent RH% reading.

Did you get the "miniature" chart for reading the "dry bulb" and "wet bulb" temperatures, then read off the RH value. recopy that chart and blow it up for easier reading, like 125 or 150%

[Merc]

The reference numbers chart is on the instrument case. Good idea about using room temperature water. I wet it from the sink and wait a while until both thermometers equalize which takes a few minutes. What the psychrometer tells me is that my furnace humidifier (a) is working, and (b) the humidity controller is accurate.

[jjrothWA]

Change or clean the wetted surface on the humidifier, helped a friend with his and the entire unite was plugged.

Made a weak muratic bath and let soaked for and hour which cleared the build-up and poured the solution down the plugged drain line and cleared that.

[four cups water one cup straight from commercial muratic acid jug {OTC}]

[Merc]

My Aprilaire Model 110 humidifier from the 1970s stopped working a few years ago. I ordered a maintenance kit from Aprilaire that included a new orfice and wetted surface. After disassembly, l discovered the orfice was totally plugged with calcium. I replaced all the old parts with the parts furnished in the maintenance kit and it’s been working fine. Just for fun, I dropped the old orfice in a pan of vinegar and the calcium deposit dissolved almost immediately.

One thing I’ve always wondered about was why the manual humidistat specifies changing the humidity setting based on outside temperature:

35% = plus 25 degrees
25% = 0 Degrees
15% = minus 20 degrees

The overall range of settings - 0 to 50%.

Why would I want to allow the humidity in my house to be as low as 15% regardless of outside temperatures?

[Merc]

Something else I found out about manual humidistats. You can use them to determine the actual RH in your house by slowly turning the control knob CW and CCW and listening for 2 clicks. The actual RH is supposed to be between the clicks. Comparing the 2 clicks to my psychrometer reading, the clicks occur at around 35% RH, the humidistat is set at 40% RH and my psychrometer reads 40% RH.