We're moving our office space and doing a lot of the build-out ourselves. In our HVAC overhaul, we need to replace the manual thermostat with a setback model. So I bought a Nest b/c I read about it, and it sounded great. That, and it looks cool.
Our HVAC guy ripped it, though. 'Said that they don't work, they don't really do what they're supposed to do, 'worthless, and the company that makes them is being sued.
'Haven't done a lick of checking on any of this, but I wanted to touch base with this knowledgeable group first. Does anyone have any experience or knowledge about the Nest they can share?
A standard FF kit will shut off the condenser and turn on the furnace with a call for AUX heat, regardless if the thermostat is giving a Y call or not. Some FF kits have external thermostats to set the balance point where it's more economical to run the furnace. Pull the data sheet/installation instructions for your FF kit off the Honeywell website.
Did your installer have reason to think the Nest wouldn't be compatible with your system? I'm surprised your installer would have not used the DF capability built into most of the newer Honeywell stats instead of adding a separate FF kit. Most stats over $100 have DF capability built in, no separate FF kit required.
In Oklahoma gas prices are so cheap (40 cents per therm) that running a heat pump makes no sense unless you have an all electric house. Our local gas company builds most of the charges into the $27/mo meter fee. So for us it's either make your home all electric, or have as many gas appliances as possible. Most homeowners with DF setups give up on the heat pump once they feel the warmth of the gas heat.
How does the AUX lockout work? Can Nest be set to shut off heat pump when 2nd stage (aka aux heat) is activated? Can Nest be set up to lock out compressor and run 100% aux heat below a certain outdoor temperature? If Nest can be set up to not run AUX and heat pump at the same time, I don't see why it's not compatible with duel fuel.
Some background info and then the answer at the end, Bob.
AUX lockout = AUX is not needed when outdoor temp is warm. This cutoff depends on how efficient the system's heat pump is. A user can set an outdoor temperature that they do not want AUX to be used if it is warmer than that. The temp range is xx to yy.
Since the heat pump produces positive heating even when it is colder, when AUX kicks in, it is still a good idea to keep the heat pump on. So the heat pump does not get turned off just because AUX is on.
There is another lockout temp that Nest offers called "compressor lockout." This is an outdoor temperature that a user can set: below this temp, only AUX will kick in. The temp range is zz to pp.
Dual fuel works by not having compressor and alternate heat on at the same time.
Between AUX lockout and compressor lockout temperatures, compressor and AUX are commanded to run at the same time.
It is theoretically true that you could set the AUX lockout and compressor lockout temperature to be at exactly the same temperature and have the effect of controlling dual fuel. However, due to some fluctuation in outdoor temp it is not a good idea to have an overlap between these two lockout temperature when they have a strip heat as their alternate source (not dual fuel). So we do not offer temperature overlap between AUX lockout and compressor lockout. This is the reason why we do not offer dual fuel support as is at this point.
Why not make a a setting for "allow compressor to operate with aux heat". It can be set to shut down or enable the compressor depending if the customer has a DF setup. It would be a simple setting that could be done with a software update. Most thermostats in the same price range of the Nest have this capability.
Most DF setups have a separate FF module designed to work with a standard heat pump stat (electronics or mechanical). Why won't the Nest work with the FF kit?
most bang for $50 bucks: http://www.prothermostats.com/product.php?p=luxpro_psp722e&prod...
The thermostat you linked to was $104, not $50. If it was $50, it would be a bargain though...
IMHO this one is well worth the additional $25:
i only paid 50 bucks for it 3 yr ago: http://www.titanicimports.com/store/luxpro-psp722e-everything-progr... here, it is 58
I've not been impressed with Lux products overall, but for $58 the stat you linked to looks like it may be a winner.
Nest lands a utility deal! : http://www.theverge.com/2012/6/25/3116435/nest-thermostat-texas-uti...
I wonder if the utility company will in include installation or has plans to use the zigbee radio?
What equipment are you installing? Crappy equipment? Nest will run it just fine. More than 3 stages, not so much.
If you are installing high efficiency communicating equipment (Infinity or Comfortlink) you'll need the manufacturers stat. Comfortlink, while not as pretty, is wifi enabled and does a TON more than nest. If you are interested in saving energy, you'll install communicating equipment.
Lot of people find it easier and more fun to wear hats proclaiming they're green. Is this about appearances or substance?
"crappy equipment" is what is installed on most homes. Rarely do I even see VS stuff installed (1 out of 10) much less communicating (1 out of 50). Oddly about 1 out of 5 go for the 90%+ furnaces even though we are in a primarily cooling climate. IMHO the money would have been much better spent getting a VS 80% furnace vs. a 90% PSC furnace. Natural gas is currently 0.40 per therm in our area.
Communicating equipment is nice but it's cost isn't justified in most areas of the country. Of the times I've seen it installed it's almost always 2 stage and sized by the LOW stage. A house needing a 3 tons gets a 5 ton which has a 3 ton low stage. All that high SEER the customer paid for just went out the window.