Here are all the stats I could think of:
Location - suburbs of Chicago. TV weatherman said last night that weather conditions (dry and single-digits) meant inside home humidity typically about 8% in January.
Size - 2-story, 1700 s.f.
Tightness - DH just insulated all the outside walls, and it's like night and day compared to how drafty it was before. It's a '50's house, so it's still not super tight.
Water hardness - just slightly hard water, not hard enough to need water softening.

Somebody told me to get the Aprilaire 700 cause it's the one with the fan, and the fan is important, though I am not sure why. But the 700 seems to need a drain nearby. The 400 doesn't have a fan, but doesn't need a drain. DH will do the installation (he is very good, he just finished our entire kitchen himself except for the granite, so I am not worried about installation). I'm in charge of purchasing, so I am looking forward to advice from you experts as to brand and model. TIA.

Aprilaire 400 that doesn't need a drain nearby

Aprilaire 700 that has a fan

What I'm getting at, is that whenever you do replace it, it will likely be a high efficiency unit(> 90% efficiency), which will require a condensate drain. If it is located in a basement or utility room where you do your laundry, the condensate can be drained via a wash tub or standpipe. Worst case, you may have to buy a condensate pump (probably less than $100 at a home center).

If you go this route, make sure that the pump has an overflow safety switch, which should be wired through the furnace's 24v supply. This way, if the pump fails (or stops for some reason), you will not get a flood.

Another thing to consider: Units without a fan other than a drum type (not too many of those around), utilize a bypass duct to draw hot air through the wet medium, then back into the return air stream. This amount of air is 'stolen' from the supply air. With a 1, 2, or 3 stage furnace, it's not a problem. If you are considering a modulating furnace, which runs mostly at relatively low fan speeds, it could be a problem.

You might want to hook it up to the hot water supply.

Good luck.

V

http://ths.gardenweb.com/forums/load/hvac/msg0112274923415.html?1

Choose whichever unit you feel is best, based on its specifications and your needs. I'm not familiar with the model 400, but the idea of not having a drain makes me nervous. I seem to recall reading posts on another forum, where the PROs didn't think too highly of it.

Living in a cold winter climate, when my HE furnace was installed, I specified that the condensate be pumped laterally about 20 feet, then up about 20 feet to a first floor laundry room, to avoid freezing problems.

A little giant pump (probably closer to $50, could easily pump your waste water up to the ceiling via vinyl tubing, around the perimeter, or directly to your tub.

V

It would be helpful if you indicated the make and model # of your furnace. Also, any information on the pump if available.

Actually,household condensate pumps are small in size. At some point, ANY condensate pump will be full and switch on.
There is a float inside the pump which activates it, when in the 'up' position. Should it become stuck by crud or whatever, the pump will eventually overflow.

Check to see if there are 2 wires on the pump that are capped or taped, with no connection. A pump without a safety switch, is an accident waiting to happen. Think about this: If your furnace is producing condensate, and your pump becomes stuck (with no humidifier adding water), it will overflow.

V

The humidity is now consistent at 40% which is where I have it set. I have bought a couple of extra "water panels" because they recommend changes twice during the heating season.