Yes its installed wrong, fan powered units such as this needs to be on the supply plenum (which appears to have no room) In this case a bypass type humidifier should have been used.

You could try supplying it with hot water for improvement, but at a energy cost to you.

It is supplied with hot water, but that really makes no difference. Even with it set to just "On" (humdistat dial goes up to 60% and the next mark is "On") there is no change in the RH level in the house. If I set the thermostat to 70 *F from 65 *F and it runs for a while, the humidity actually goes down in the house.

Since it is installed incorrectly, I feel like the heating and cooling company that installed it should be giving me a refund, or installing a bypass-type humidifier at no charge. However, I've read that the bypass-type humidifiers are even less efficient that than the fan-powered type that I have now.

It just doesn't make any sense to me that a supposed "trained professional" would install it this way. It's obvious that any of the moisture that's added to the air in the return before entering the furnace is removed when the air is heated, completely negating the point of the humidifier in the first place.

Yes, the system is installed incorrectly. there is insufficient heat to evaporate enough water to properly humidify a home on the return side of the system. but the statement that any moisture added to the air before entering the furnace is removed when the air is heated is wrong. moisture is never removed. the humidity % of content is changed when air is heated, due the amount of moisture capability of the air temp, but the moisture itself is NOT removed by heating.

if this were my house, and humidity is required, I would have a steam humidifier installed. far better moisture volume intake, and much simpler installation.

Bypass humidifiers are not less efficient than fan but since they use bypass air across the heat exchanger, can effect the unit fan and heat efficiency. This holds true for AC unless a damper is closed, however a great argument could be made that extra bypass air is beneficial to humidity removal.

Thanks, guys.

vstech, sorry, I guess I did not understand RH correctly when I originally posted the question. After more reading I see that when the air is heated, it's ability to hold water vapor increases, and because of this, the RH drops.

I've done a lot of reading at various places, and so many people say it is OK to install a powered humidifier on the return plenum. I just don't get this thinking, even when tapped into the hot water. In the supply plenum the air temperature is what, around 120 *F or more for my gas-fired furnace? In the return plenum it's probably no more than 70 *F. It's obvious that the return plenum is not a good place to install a powered humidifier.

I would love to have a steam humidifier installed, but that's a lot of money, especially since I've already paid for a $200+ humidifier + installation (indirectly through buying a new home; the builder paid for it, and passed the cost to me, and then some, in the price of the home). In my opinion, the heating and cooling company that installed this owes me.