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Needs calibration to ensure temp accuracy
on March 11, 2012
I ordered three Lux TX1500E thermostats. Before installing I tested them for accuracy by placing all three Lux thermostats side by side, and comparing the temperature and humidity readings with two additional thermostats and hygrometers I know to be accurate.
All three Lux units displayed different temperatures from each other. One of the three units was accurate. The temperature is easy to calibrate by setting the dial to run mode, and while holding the up button, pressing the down button once. A screen pops up allowing the temp to be set plus or minus five degrees. In this case the temperature on one of the units was 2 degrees high, so I entered -2 on the calibration, and since calibrating the temperature readings have been accurate.
The humidity readings for all three units were initially off by up to 7 percentage points. The unit allows for calibration up to +/- 15 percentage points by setting the dial to run, pressing the H button, and while holding down the up button, pressing the down button once. After calibrating the units, they are still off by a couple percent, and occasionally display a ridiculous reading like 95% relative humidity (RH) when the actual RH is 50-60%, but for the most part the RH is close enough.
The humidity reading on the unit does not display automatically. The "H" button must be pushed to display relative humidity. To clarify, the thermostat runs off temperature only, i.e. there isn't an option to run the air conditioner until the relative humidity reaches a certain level.
The display on the unit is puzzling. On the left the time is displayed prominently, and in a much smaller font the temperature displays on the right. A more helpful display would be: Actual temp, Set temp, and actual humidity all in large lettering, and then the time somewhere off in a corner.
The reason I bought a programmable thermostat is for the swing function. My old thermostat would constantly cycle the a/c (on for only 5 minutes at a time) because it was turning on the unit when the temp hit 79.25 degrees and turning it off when it hit 78.75. This 1) damages the a/c equipment, and 2) does not allow the a/c units to run long enough for effective dehumidification to occur, since the a/c doesn't really start to dehumidify effectively until it has been on for at least 10-15 minutes. Without proper dehumidification, the house feels warmer than it is (i.e. it's not the heat, it's the humidity).
This Lux thermostat has a default swing function of 1, which means that if you set the thermostat on 79, it will turn on the a/c at 79.25 and turn it off at 78.75 degrees. The swing function can be set between 1 and 9. Using a 79 degree setting, a swing value of 4 means the a/c will turn on at 80 degrees and turn off at 78 degrees. A swing value of 8 means the a/c will turn on at 81 degrees and turn off at 77 degrees. I don't understand why the default swing is at 1 (i.e. .25 degrees). A setting of at least 4 (i.e. 1 degree) seems prudent for the health of the a/c equipment and humidity control.
Moving on, I purchased this Lux unit instead of a Honeywell because 1) Consumer Reports gave the highest rating of all tested thermostats to the Lux TX1500E, which rated much higher than the Honeywell units, 2) These are $40 vs. over $100 for the Honeywell units, and 3)I called tech support for both Honeywell and Lux. Honeywell routes you to an overseas call center staffed by people who barely speak English. Lux has a call back system, but they called back within two hours, and the guy I spoke with was intelligent and located in the U.S.
Before purchasing I also considered the Lux TX9000TS, which is a touch screen thermostat that received Consumer Reports' second highest rating, right behind this unit. I purchased the TX1500E instead because 1) better pricing, 2) I read the 1-star reviews on Amazon for both products, and the TX9000TS seemed to have more problems than the TX1500E, and 3) The manual dial/arrow key set on the TX1500E is more intuitive for me to navigate than a touch screen.
I found programming the thermostat to be easy, although a little tedious, as the program settings must be entered 4 times (once for weekdays, once for Saturday, once for Sunday, and last for Special Programs).
One feature I'm not thrilled with is the fan setting. The fan can be set on "auto", meaning it runs only when the a/c or furnace runs. The other fan setting is "on" meaning it runs continuously (potentially causing some major humidity problems during the cooling season in a hot/humid climate). What I would like to have seen is a "circulate" option for the fan, meaning if the a/c or furnace hasn't kicked on in the past 30 minutes, the fan will circulate the air for 5-10 minutes in order to improve indoor air quality.
With a fan setting of "on", let's say the a/c has run for 20 minutes and the a/c coil now has water dripping off it. If the fan keeps running without a/c, much of that condensed water on the coil is going to re-evaporate into the air that the fan is blowing over it, which will raise humidity, partially defeating one of the two functions of air conditioning (lower temp and lower humidity). At least this is what happens in humid climates such as Houston where I'm located. A "circulate" function on the thermostat would avoid this problem.