FYI, I meant to add that I'm getting heatpumps, not fuel-based furnaces.

Aprilaire makes terrific products (air cleaners and humidifiers). I have an Aprilaire Model 600, which is their most popular one. If you have forced air, than this type of piggy-back design would work very well.

The Model 600 is self flushing/cleaning so it requires maintenance only 1X or 2X per heating year, which is simply installing a new evaporation pad and wipe it down. One note, because this will be used on a heat pump, which doesnÂt get as hot as a fuel based system, make sure you use the HOT line, not the cold line for the water input. This will improve the efficiency greatly.

Also, if you are concerned about water usage or do not have a way to drain excess water, than go with their Model 400 which self contained and doesnÂt require a water drain out.

Skuttle offers a timer which flushes the humidifier every two hours, thus eliminating standing water.
http://www.skuttle.com/product.html
But check out EWC:
http://www.ewccontrols.com/steam_humidifier.htm
...
The advantage of most Aprilaire models is their simplicity, easy maintenance, and relatively low cost. The disadvantages are that they require constant running water and they will only operate when the furnace runs.
When you jump up to a steam humidifier, it is expensive, and it can require more maintenance esp. if you have hard water. But it operates whenever more humidity is required.

Steam is the only way to go. It will not leave that white residue that non steam units do, and because they actually boil the water, they are much more sanitary inside. I just replaced my EWC 110 volt steam humidifier with a 220 volt skuttle steam humidifiier in my personal house.

What part of the country do you live in? I STRONGLY suggest that you make sure you spec and install a 220 volt unit. Even in Southern California, the performance of the 110 volt (12kw) unit was dissapointing. The unit could run for hours and never satisfy the humidistat and shut off. Since changing the unit to the higher steam output 220 volt model, the performance has improved incredibly. Unlike A/C, oversizing the steam humidifier is a good thing (within reason).

For what it's worth, both the EWC and the Skuttle both drain off the water to prevent junk from growing inside. The EWC drains completely after use and the water has cooled to below 140 degrees. The Skuttle has a programmable timer that opens the drain valve for 10, 20 or 30 seconds every 30 minutes depending how it is set. Both brands will turn the furnace blower on independantly of the thermostat to humidify the house if needed. You have to remember to shut down the unit for the summer because you dont need it runing during cooling season - it will put extra load on the A/C

I had a lot of problems with my EWC steam unit and can not personally reccommend it. The Skuttle that replaced it is a lot simpler of a unit and has given me NO problems.

I ended up buying my Skuttle brand new in the box on eBay. Make sure you get a good digital humidiatat with an outdoor temperaure sensor that adjusts the indoor humidity based on the OSA temp.

www.ewccontrols.com

or

www.skuttle.com

Just keep in mind that steam humidifiers use electricity (120V or 240V for larger models)to heat the water and turn it into steam. Calculate in the cost of electricity usage when comparing models too.

All good advice. No yays or nays.

Just MHO.

We have H/W baseboard heat. Very dry during the colder months.

We have a Aprilaire 350 with hot water directly into the unit. Duct work to 2 areas of the house. We can keep the humidity at 35% and as high as 45% during the winter months and only replace a water filter cartridge and screening unit once a year.

Works great.

Some humidifier manufacturers (including Skuttle) in the past had standing water designs. They did not heat the water. Many are still in use. Many are still repaired, not replaced. These are the ones that have problems.
They are no longer manufactured.