Honeywell RTH8500 T-stat

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Rfsmith48

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Folks,

Just installed this thermostat. We like it.

The wireless interconnect is nice.

Is there an Internet users group for this device? (Or similar devices?)

The Tstat has a "Heating Cycle Rate" setting for a variety of furnaces. The Tstat owners manual does not explain the operating difference between a Standard furnace (less than 90%) and a high efficiency furnace (90% or higher). What does the Tstat do differently between these two settings?

TIA,

Rog Smith
 

DonL

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What is the Model of the furnace you have it connected to ?

There may be a Yahoo forum that has more info.


Good Luck on your project.
 

Jadnashua

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FWIW, each time you shut your furnace off, you tend to lose some of the heat you paid for up the flue or into maybe the basement (that's not a total loss, though). The same is somewhat true when you start it back up again...it isn't as efficient immediately after starting as it would be steady state shortly after. So, under ideal conditions, the thing could modulate to your needed load so it was adding just enough to overcome that heat that is lost, but most furnaces, if they have any adjustment, it is maybe a two-stage furnace. It is a tradeoff between comfort and efficiency how often the furnace runs. You could turn it on every time the temperature drops .25 - 0.5 degrees, or set it for more. You'd be more comfortable with it lower, but your heating bill be smaller if you let it be a bit more. The furnace itself will last longer if it doesn't short-cycle a lot. Things work better when they turn on and stay there, verses short on/off/on/off sessions.

SOme of the thermostats have an internal timer, and regardless of how far the temperature drops after a heating cycle, won't turn it back on again until that timer has expired or the temperature drop is what some may consider excessive. On some, you can play with that setting to match things up with your comfort levels and pocket book and come to a compromise. I do not know the specifics of how that one works, but this may help you understand the basics.
 

DonL

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As far as I can tell that is a Smart Thermostat. It can save money, in smart mode.

But it can not change the efficiency of a furnace.

Unless some magic is involved.
 

Rfsmith48

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Guys,

Thanks for the comments.

I found a good Tstat forum on Yahoo.

To clarify: I understand that the Tstat cannot improve/change the furnace efficiency. My question is: What does the Tstat do differently between the Hi/Lo furnace efficiency settings?

I will post on the http://www.thermostatforums.com/forum.php website, as well.

Thanks again!

Rog
 

Jadnashua

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The amount of hysteresis and the cycle lockouts based on how tightly it controls the temperature will affect efficiency and longevity of your equipment in addition to your comfort levels.

Under ideal conditions, your hvac system would be able to modulate to exactly match your heat loss or gain and run continuously. In the real world, that isn't easily accomplished. Things get much worse for efficiency when your hvac equipment isn't matched closely to your real loads. With fixed output devices, that match may only happen once every few years, so compromise is the norm.
 
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