The furnace mounted humidifier had the water line feed connected to the hot water line from the water heater. Should it be on the hot side, cold side, or does it matter?
I would say cold. Lets see what the experts say…
I would say the same as James!
Reason is it is a breading ground for bacteria. According to knowledge humidifiers should be cleaned at least weekly and you will never find them clean unless they are the type with self-clean features. Hot water would be worse and create even more bacteria in the water tray containment area.
I agree .
In Canada we need dehumidifiers most of the year .
Humidifiers are a great place to breed bugs and the whole Family has no idea why so many are sick so often … Roy
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Excellent responses - Thanks!
I agree with the negative assessment of humidifiers - they create more problems than they are worth. But you will find a lot of them plumbed to the hot water under the assumption that more water will evaporate. In practice, the water cools faster than it is used.
If you have a whole house humidifier installed, be sure it is on the return air ducting. It is never a question of if a humidifier will leak, but when. If installed on the supply ducting the leakage will be onto the heat exchanger causing rust and premature deterioration potentially allowing combustion by products into the home. Newer high efficiency heat exchangers are constructed with stainless steel and designed to cope with condensate but still not a good idea to rain water down onto the thing.
Chad, Thank you for answering the asked question! 
Hot - Cold water supply does not matter for most humidifiers.
Some steam generator types back flush and use a lot of water at one time and may effect the sensors, but the other kind never see the water hot.
Thanks to all who responded. Based on what I read here, I think it would be best to yank the humidifier and explore other options. Happy New Year!
Hot side is better as it will vaporize more readily than cold water.
Some might think it best to remove the humidifier but that is wrong for my area.
We heat very cold air here and without some humidity it becomes very uncomfortable and you have a lot of static electricity build up.
It is important to control the level of humidity as the temps change throughout the season to prevent condensation on windows and frames.
This can be done manually but an automatic system that senses outdoor temps is more reliable.
I agree with ALL that Michael (as long as the hot water hasn’t passed through a water softener)
Maybe it depends on the region but many humidifiers in my area are operating on hot water because it increases the humidifying capacity so much.
The down side is 1) a little more lime/calcium build up to clean out of the orifice at the annual fall start up than there would have been with cold water and 2) Self cleaning humidifiers do run a little water down the drain when operating in order for them to be self cleaning and it does cost a little to heat water then run it down the drain but that is really pretty minimal. The main thing is that there is no water left in them when they turn off so no weekly cleaning necessary.
Most of the old time humidifiers had standing water in them and did need constant cleaning so I think that left bad impressions on folks that now say all humidifiers are included in that group.
The author in that link that James provided evidently was thinking along the same lines since the picture in the link was one of those old style humidifiers with the little cesspool.
A good self cleaning humidifier such as General or Aprilaire for example will not have bacteria and will only need maintenance once a year at start up.
I realize that many things are different in different parts of the country, so what works great here in the Midwest may not necessarily be the best way to do things in other regions.