I use a moisture meter I got at Harbor Freight for 19.99, and it seems to work fine. At least, it reads high for obviously wet wood and low for obviously dry wood. I've never tested it against a higher-priced one.
If you put a pen blank on top of your hot water heater, it will dry relatively quickly. My experience with this (gas water heater) is that it goes from about 14% to about 7% in less than two days, with no damage to, nor distorting of, the wood. I think 7% is about the equilibrium moisture content for this area, so that is what I would shoot for.
Some people say if you hold a pen blank to your cheek, and it seems cool, then it is too wet. I tend to agree with that.
Joe