Rite Temp GPMG8085C: Informal Review

Who would've thought that this blog would be one of the most often referred to sources of information about GPMG8085C... All right, if that's what y'all want...

Ever heard of "The Golden Triangle"? "Good, Cheap, Fast - Pick Two". So, this thermostat may just as well be the closest approximation. $20 cheaper than the next guy (Honeywell RTH7500, I'll come back to it another time), does the same job, if not better.

Comparable quality and length of DIY installation.

Installation complexity: no-brainer (YMMV). A few advices, though:

• Make sure you RTFM;
• Don't drop the wires into the wall;
• Programming is best done when the thermostat is laying on the desk before you, not when you're standing next to the wall with the thermostat on it;
• At least for me, the preinstalled battery still works after a few months of operation, may want to ignore that paranoid advice to remove it.
  

Significantly bigger and nicer backlit touchscreen than the competition has (to be completely fair, they do have a big touchscreen on VisionPro, but that one is almost twice as expensive, so no cigar), and it has a nice textured button that you can grope (English experts, give me a non-ambiguous word and have my thanks in return) in the dark without being afraid to push a wrong button and reset something.

You have to really hate your customers not to provide an option like that (example: RTH7500 needs you to press any button, and, invokes the action corresponding to that button, even in the dark. So you have to be really careful where you tread, and the fact that the screen is backlit is useless - you can't comfortably use it anyway).

There's a stylus and a holder, but feel free to ignore it - fingers and/or fingernails do the job just fine. No visible scratch marks after few months of use.

7-day programmability is certainly nice, but the schedule selection is really weird - you can't set the schedule boundaries at arbitrary time, but only at one of two settings (forgot what times exactly, will update later). Kind of inconvenient, and this is probably the most annoying feature, or, rather, lack thereof. Competing device shines here - you can have your heat and cold any time.

Side note: I'm wondering why nobody figured yet that anticipation is something you're quite willing to have for a period starting, say, at 6PM, when you return from work, but not really want for the period starting, say, at 9PM - when you are on a time of day electric plan, which makes energy after 9PM three times cheaper than before. Remember, you read it here first.

If you don't need 7-day programming, there are other, cheaper Rite Temp models that offer compatible feature set, but 5+1+1 or 5+2 day programming.

I'm quite willing to forgive lack of schedule configurability for including an extremely important feature - you can manually change the hysteresis. Setting it to the maximum value makes the temperature spread quite noticeable (up to 5°F), but makes the unit cycle about three times less often than it would otherwise do. Don't have equipment to measure the actual gain, but would certainly recommend this thermostat to people who are either energy conscious and don't mind little discomfort, and to people who have grossly oversized units - you guys may suffer from temperature swings even worse, but at least your electric bill will drop like a rock because the unit won't breathe like a dog outdoors in Arizona summer anymore.

Can't say anything about humidistat - not much use for it in the middle of Arizona summer.

Another useful feature - filter usage counter. Depending on the climate, your unit may cease operating for a couple of months in mid-season, so you can afford to buy a higher quality, more expensive filter without a fear that you're wasting money (just think of how much it'll cost you to clean the inner coil when the time comes, and reconsider buying that inexpensive $3 filter).

You definitely need to read the manual provided with it in order to learn to operate - but then again, this is true about any more or less complicated home appliance - it takes significantly higher IQ to figure out how to connect the 5.1 home theater and the rest of components together without electrocuting oneself, so no big deal here.

At least all the settings have icons assigned to them, and you can figure out what is what, unlike some other designs, where features are indicated with numbers (come on, it's not 1960 anymore...)

Bottomline

Well worth the money I paid for it.

Disclaimer

God, what have we come to... Anyway - use your common sense, don't do stupid things, and read this first.

Thermostat Wars

The predominant kind of thermostat war is the one between those who understand the concept of the thermostat and those who don't. It is difficult to believe, but there are still people who don't get it. They would crank the thermostat all the way down when they feel hot and all the way up when they feel cold. I kid you not, several years ago there was a guy who came to the Residential HVAC forum with a question, "how to educate the significant other not to do that". After few days and several dozen messages, the community agreed that the only way to deal with his particular problem was to install a fake thermostat. This case is beyond repair, let's concentrate on the other.

Out of remaining, two kinds can be distilled: those that require marriage counseling and cause HR violations , and those that don't. The latter is the kind I would like to cover in this article.

The final division is the wars between the occupants of different rooms, and, those apparently happening just in the mind of a single person waging the war.

The first kind is actually pretty easy - this is what the zoning systems are for. I mean, the real ones that do allow you to set different temperature for different zones.

As for the last kind... Imagine a situation when there's a person who claims they are absolutely comfortable with a certain temperature - let's say, for the sake of argument, it's 78°F. And indeed, when put into a scientifically controlled environment, they feel just fine. But in real life...

They fiddle with the thermostat all the time. Sometimes they push it up. Sometimes they push it down. Sometimes, they claim the thermostat is not calibrated (it is). When cornered, they are claiming the temperature is not right, and demand a precision thermometer. And you know what?

Most of the time they are right.

The cause for it is trivial from a control systems engineer standpoint, but is carefully hidden in a plain view for the rest of the world.

Almost all thermostats, except the very advanced ones, are based on a very simple concept of a hysteresis. Temperature goes X degrees above the setpoint, cooling on. Temperature goes X degrees below the setpoint, cooling off. Simple?

Not quite.

First of all, not all thermostats (as a matter of fact, very few) will let you change X. According to some claims (google it up if you want), X = 2.5 (I suppose Fahrenheit) for mechanical thermostats, somewhat less for digital. 5°F spread is a lot.

Side note: Rite Temp GPMG8085C (and possibly other Rite Temp thermostats) will let you control hysteresis. Doesn't mean I endorse it, though - it's got its quirks. Doesn't mean I condemn it, either - it's doing a good job comparable to Honeywell RTH7500 for $20 (20%) less.

Then, the situation gets very interesting as temperatures get milder. The closer is the ambient temperature to the setpoint temperature, the more suffering there is (that'll be mornings, afternoons, and the whole mid-seasons). The reason?

Deviations of ambient temperature are sufficient to cause severe discomfort, but are not sufficient to kick the temperature at the thermostat beyond the dead band and thus to force the HVAC unit to actually do something.

Things can become really bad if the house is big enough, and the part of it where the thermostat is is insulated better than other parts - all in all, "mild" is a relative term. A typical case would be a tri-level house somewhere in Arizona.

Which is where and how it all started. Is there an answer? Yes, and it's been already implemented several years ago, but I'm not telling. It would suffice to say that if you want to find out, by this time you know where to look for it.