Less water wasted, more maintenance

Aprilaire 400 is a bypass humidifier, as opposed to flow through. Unlike the Aprilaire 500 and 600 it's design reuses, rather than discharges, excess water. Water flows down through the evaporator pad as hot air passes through the pad. The excess water collects in a small pan at the bottom. Two separate water level sensors cut off water flow.  One if the pan has water in it, and another if the pan is going to overflow. Because of the wicking and the water level sensors it is very unlikely the unit would overflow making a drain to a sewer unnecessary.

Reusing the excess water is nice if the the unit will not be mounted near a drain. Unfortunately reusing water requires the evaporator to be replaced more often as the excess water does not wash out the collected mineral deposits. This will be an issue if you have hard water. Before the water enters the unit it passes through a strainer, using less water might mean less clogging of the strainer. I have no problem with the 400, but you might like the cheaper 500 or 600 as they only require one evaporator change per year. Needless to say if something went wrong and the drain was clogged the 500 or 600 might make a mess.

Installation:

I paid $715 with installation, about 4 1/2 hours labor and some additional parts. Because I had an older furnace the installer had to get a 'current sensing switch', which was not included with the unit. Installation included a pvc drain line to a basement sink. You could get away with a drain to a bucket, saving about 3/4 hour labor, as the unit does not expel any water. A 'leak frog' or other water alarm in the bucket might be a good idea.


When to replace the evaporator pads:

The unit has a little light that notifies you when the evaporator needs replacing.  The light is really a kind of counter that records the number of times the electronic water valve opens, it does not actually test the filter.  You will notice that the house feels cold when the filter needs replacing, because it stops humidifying.  You should also buy a hygrometer to measure the moisture in your home.  I bought one of those weather stations with a thermometer, barometer, hygrometer that hang from a wall for $20 inc s/h from eBay seller myestuff-usa.  There are also digital ones for about the same price.  When the moisture dropped below 40% I knew the humidifier stopped working and descaled the evaporator pad(see below).   

My experience with it:

After about 2 months of use the house seems hotter than before it was installed. Due to complaints about it being too hot the thermostat was dropped from 70 deg F to 68. Even though people think it is a joke, dry heat feels cooler than wet (humid) heat even though the temperature is the same. I have not seen any sign of water in the drain tube so the water saving features do seem to work.

Filter replacement:

In my case replacing the filter after 3 months was necessary. After about 3 months of operation in Brooklyn NY the bottom of the filter was covered with 'scale'. The unit was set on the highest level (7) as the house is un-insulated, balloon construction, aka loose. The scale prevented the wicking of the water back up the filter, which also caused the unit to stop supplying more water, as the pan on the bottom was always full.

Filter replacement is more tricky than it looks. Carefully read the instructions on the box a few times as there are things you can break, and which things need cleaning, and which shouldn't be cleaned, are not obvious. The house feels noticeably hotter after filter replacement.

In retrospect I think a unit that required only one filter replacement per year would have been better as I have a drain near by and water is not expensive in NYC. I would avoid this unit unless you are able to faithfully do the filter replacement and cleaning, or hire a competent person to do it.

Note a competent person is someone with a 'light touch', that is able to read instructions first, and then follow the instructions. For example an English speaking baby sitter might be better at it than a non English speaking handyman. In any case do it the first time yourself so you know what needs to be done.

Descaling the evaporator pad:

It is possible to descale the evaporator pads.  Because of the cold winter, the evaporator pad clogged early.  Rather than buy new pads I decided to try to descale them.  There are 2 things you can do.  First just take the pad out, drain the water in the pan at the bottom, and re install the pad upside down.  The scale forms mostly at the bottom of the pad where it stops water from being absorbed from the pan, so reinstalling it upside down solves the problem for a while.  The second thing you can do is descale by putting about 1 table spoon of Citiric Acid, Tri sodium phosphate, or even vinager into a basin about the size of the pad filled with hot water.  Gently dunk, let soak, and remove the pad a few times.  Repeat once in fresh water.  Be careful as the paper pad is very fragile.  After the pad is clean reinstall it in the humidifier.  And finally I placed a Humidex tablet (see below) in the pan.  Please note this is my own descaling procedure based on 2 heating seasons experience, and is not suggested by the manufacturer, so beware. 

Citiric Acid is used to descale espresso makers and is sold were spices are sold.  Also called sour salt or lemon salt.     

Tri sodium phosphate (TSP) is used to descale espresso makers, and for general cleaning.  It is the main component of JoeGlo and  Humidex tablets.  It is sold in bulk at paint supply stores for cleaning walls.  I use 1 Humidex tablet that I bought at an HVAC supplier.