Nest and Tacos

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Old 11-29-12, 09:24 AM
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Nest and Tacos

I just bought a new (very old) house. It has hot water radiator heating. It has been updated and has a fancy 3 zone Buderus boiler and 2 air conditioning (forced air electric) units for a total of 5 thermostats (2 air and 3 heat - all separate).

My goal is to get down to 3 thermostats (combine 2 of the heating and cooling thermostats) and I thought I would start off trying a Nest thermostat since it looks pretty cool. The heating zones are controlled by Taco 573-2 valves and they are wired as per Taco instructions with a single red and white wire going to each thermostat.
The system seems to work fine (it's slow to respond to increase temp but that's what I would expect for radiator) but when I looked at the existing thermostat for the heating the switches on it are for warm air furnace instead of hot water/high efficiency. Is this ok... it seems to work?

Will the Nest thermostat work for this kind of heating system and are there setup options I need to select during the installation for this type of system? Thanks for any answers.
 
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Old 11-29-12, 04:42 PM
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when I looked at the existing thermostat for the heating the switches on it are for warm air furnace instead of hot water/high efficiency. Is this ok... it seems to work?
Set it up correctly and see if it works better!

I only know about the Nest what I've read on the internet... yeah, bells and whistles it seems to have. Whether or not any of that "IPhone" stuff is of any real use remains to be seen.

I can't say that I have heard anyone raving about how wonderful they are. But have heard a few negatives... which is typical for product reviews on the internet. Nobody gives GOOD reviews because they are happy and go about their lives... but boy, if someone gets a bee in their bonnet about something they can sure write a bunch of negative reviews!

Hopefully someone with some real experience with the Nest will come by and give you some input.

My personal opinion is that a thermostat should be just a thermostat. Making it all techie is overkill. I would advise a nice Honeywell VisionPro job...

There IS a forum on DIY that caters specifically to thermostat questions, you might try asking there.
 
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Old 11-29-12, 06:07 PM
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Should not be much of a problem as long as the nest has an Rh and RC that are seperate.
There should also be setting to control the cycle length (that is what the hot water vs forced air does).

You will need to make sure that you can get the wires from the heating zone to the cooling zone or vice versa.

I have no real world advice as to the nest as a product, but if you want to try it.. why no go for it. It's only money.

Unlike Troop, I love gadgets... Controls are my friend :-)
 
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Old 11-29-12, 07:43 PM
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Relays

Hi,

I just installed a nest on a Bosch boiler (will be similar to Buderus) and had to do a lot of research regarding correct wiring.

My recommendation would be to find a permanent 24V source (perhaps your AC R / Rc and C terminals) and run this to the Nest Rh and C. This will provide the Nest with the required power without having to rely on funny switching themes to keep its battery charged. If your AC does not have R / Rc and C, you need a separate transformer.

The Nest instructions say that Rh and Rc are internally connected, so I used Rh as recommended. Any R wire is a 24V power source, the other side is C (common).

Wire the Nest Rh to the R or Rc and the C to the C of the power source (the AC terminal or a separate transformer). This will power the Nest. Use the W1 terminal on the Nest to connect to a 24V relay coil, the other side of it goes to C. The Nest will energize this relay when HEAT is called. For AC, replicate this with a second relay between Y1 and the same C.

Connect your boiler thermostat input (two wires) between the first relay COMMON and NO contacts.
Connect your AC thermostat input between R and Y.

This will do the trick and electrically separate the AC and boiler inputs, which is important. You don't want to introduce the wrong voltage into your expensive boiler board.

I had no AC to borrow the power from and found a "fan control center" Part 2E852 from Grainger, which is a 24V transformer and one relay mounted on a 4" square junction box cover, to provide my stat power and heat relay.
This required two junction boxes, one for line voltage and one for low voltage.
Mount the fan center on one 4" square box and make the line connections inside. Run the relay switch wires, one side of the relay coil, and transformer R and C into the connected box (through a chase nipple).

A lot of wiring, but works like a charm.

Good luck
 
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Old 11-30-12, 10:55 AM
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What have I gotten myself into? LOL. Nest says that if only one R wire is connected it jumpers Rc and Rh internally, but if both Rc and Rh are connected, it disconnects them internally so they are separate. I assume this takes care of me frying the boiler circuit board with input from my cooling system if both Rc and Rh are connected and does it obviate the need for a relay? Nest says that in 99% of cases a common wire is not required. The boiler has a transformer step down that powers up to 3 taco valves. Are you saying the R wire from the taco unit to the thermostat will not be sufficient to keep the Nest powered up?
 
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Old 11-30-12, 06:26 PM
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That Nest thermostat is one pricey bugger! I do see that Lowes also has a Honeywell Wi-Fi enabled 7-day programmable thermostat for $119.00 and the nest is listed for a whopping $229.00 for the first generation and a Nest 2nd generation for $249.00!

I was wondering, do ANY of these thermostats have ANY kind of a low temp alarm? If I dropped $249.00 for a smart thermostat I would hope they have some type of low temp alarm! Looks like I might have to hop over to the thermostat threads & do some research.
 
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Old 11-30-12, 07:02 PM
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Nest themostats are being developed by refugees from Apple Computer. They are state of the art, but not in my opinion geared to DIYers who want the tech specs, wiring diagrams, voltages, etc. At $250, not sure what their advantages are. They supposedly "learn" our comings and goings, and program themselves accordingly, saving much energy. I don't think I want my thermostat learning my comings and goings, and linking it through the Internet - I don't even know my own comings and goings in advance.

And how much energy can a smart thermostat save? What is the payback period? As short as adding insulation?
 
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Old 12-01-12, 09:37 AM
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NEST with a zoned boiler system... such as a taco relay switch SR504

It can be done, but you have to add a separate 24V source and a relay for each zone. On this zoning system NEST won't recognize power because the sr504 only wants to see the circuit completed. The Taco doesn't necessarily send voltage out through the zone terminals. On MOST thermostats this fine because all the thermostat does is complete the circuit through R and W. Most thermostats don't care if they have voltage on the wires or not they simply complete a circuit.

The problem with boiler zoning and using a nest thermostat is that each system could be and usually is wired differently or uses a different type of setup.

Your system uses zone valves, and I would recommend using a C connection (there is one at each valve) to run the NEST. Nest may say that 99% don't need a C connection but I would add it anyway. I constantly see charging issues with the NEST here and at other forums. Nest really should be a professionally installed only thermostat, IMO.

For $250 X 3 = $750 I would seriously be looking at other wifi options. Honeywell has some wifi options for about half or less then that amount.



I really think Gilmorrie had a great point though. What is the payback period? What would your payback be if you spent the same amount of money on something else to make your home more efficient.
 
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Old 12-05-12, 06:41 AM
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Get an Ecobee

I have a similiar system, but my zone valves all have 24V wired to them seperate of the boiler board. I have two air handlers and 3 zones with single stage heat/ac in forced air. I had to run the C wires to the thermostats (they were there, just not connected)

I looked at the NEST and ended up buying the Ecobee Smart SI, if you are a real DIY enthusiast the SI is the way to go. It doesnt have all of the motion sensing crap, but it does have Wifi access and a website/app where you can control the temperatures, schedules, view historical logs, set vacations, etc...the best part it is only 170$, so you can 3 of them for the price of 2 Nests!

The ecobee guys are more HVAC based than NEST and you can only get their product via online stores or via a local HVAC installer.

I am not sure how much $$$ it saves me from a regular 7 day programmable thermostat, but it is useful for a few reasons

1. If I go away and forget to lower the tstats, I can always go online or to the app and set a vacation mode for a specified time

2. I have a dog and it is nice to see how hot/cold the room is at work in case I need to adjust the temp

3. I love that the SI shows the outdoor temp (via internet) next to the current temp inside - soo much nicer than those outside temp sensors they sell at CVS and such

4. The schedule feature is soo easy to use and the online portal makes adjusting a breeze


My only caution with the SI compared to the NEST is that the SI requires some HVAC knowledge (how many stage system you have, delays, etc...) but nothing too hard

It works for me great...takes a few days to learn the heating patterns so the overshoots stop pretty quickly. Feature wise they both are almost the same but the nest is more sexy, uses less weather data in its algorithms and has motion sensing, all for an added price
 
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Old 12-07-12, 09:09 AM
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I have looked into it further and the advice from ulimke seems like the only solution to replace a one zone heat thermostat with the nest.

I looked at my 3 heat zones further and discovered an interesting additional fact. The zone 1 taco valve was set in the open position whereas the other two zone valves are set in auto. I set zone 1 valve to auto and checked the voltage across terminals 1 and 2 when I turn up the thermostat to call for heat and there is 0 voltage. There is the proper voltage (24V) at both the zone 2 and zone 3 valves when these thermostats call for heat across terminals 1 and 2. At this point I will have to trace the wiring but I believe either the thermostat is not even wired to the zone valve or that it is faulty (it is an old rectangular honeywell programmable with a mercury switch and an analog clock and pin settings to turn the thermostat on and off as the clock operates (which it does not appear to do)). I also have to check that the tstat is not stuck in the off position where the clock died. My guess is that the installer set the zone valve in open recognizing that the thermostat would not complete the circuit and that heat would go to zone 1 when one of the other zones called for heat. My thinking is that it is open all the time so when one of the other zones calls for heat water would also flow into zone 1 since the valve is always open.

Zone 1 and 2 are on the same floor and the thermostats are in adjacent rooms. If this is correct I can just remove the zone 1 thermostat and replace the zone 2 thermostat and run both the zone 2 taco heating wires (rh and w) and zone 1 ac wires to this thermostat as long as there is a common wire from the ac unit to power the nest properly. This will be simpler than adding a 24v transformer and relay for zone 1 heat. Since the zone 1 and zone 2 heat thermostats are so close the only drawback would be that I would could not separately heat zone 1 and 2. Are there any drawbacks from this approach and leaving the zone 1 valve open all the time?
 

Last edited by hydrodude; 12-07-12 at 09:27 AM.
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Old 12-07-12, 04:16 PM
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My thinking is that it is open all the time so when one of the other zones calls for heat water would also flow into zone 1 since the valve is always open.
Sounds like correct thinking to me.

run both the zone 2 taco heating wires (rh and w) and zone 1 ac wires to this thermostat as long as there is a common wire from the ac unit to power the nest properly.
I can't seem to get my head around what you are describing, but it sounds VERY risky to me! Not sure I would understand it without a wiring diagram, I'm too darn 'visual'. Can you draw what you are thinking?
 
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Old 12-08-12, 04:15 PM
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Nest and Tacos

I believe I have attached a picture of what I propose to do. Here would be my steps.
1. Remove faulty TSTAT for Zone 1 heat
2. Rewire Tacos so Zone 2 controls Zone 1 valve
3. Taco Zone 2 Wires (R + W1) go to relay by AC instead of Zone 2 HW TSTAT (i.e. remove TSTAT for Zone 2 heat)
4. Replace AC1 TSTAT with Nest
4. Wire Nest W1 to relay to close circuit for Zone 2 heat
5. Wire AC common (BK) to Nest (C) and relay (power for Nest)
6. AC1 wired normally to Nest (no 2nd relay as suggested by ulimke)

Here is what should happen
a) Nest calls for heat
b) Nest energizes relay which closes Zone 2 HW circuit
c) Zone 2 HW valve opens closing contact between Zone 2 terminals (1+2) then 2+3
d) When terminals 2+3 connect on Zone 2 taco, terminals 1+2 connect on Zone 1 taco opening up Zone 1 valve which connects terminals 2+3 completing circuit for boiler
 
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Old 12-08-12, 06:23 PM
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Yes... I do believe that the diagram with the thermostat at zone 2 would work.

I don't know enough about the Nest to say whether or not the relay idea would work in place of thermosat 2 though.
 
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Old 12-09-12, 11:23 PM
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OK I think I need to shoot my home inspector. Remember I said Zone 1 Taco was set in the open mode. I checked the wires for continuity from the TSTAT for zone 1 and they are connected. I replaced the old Honeywell TSTAT on zone 1 with an old T87 Honeywell non programmable TSTAT to see why zone 1 was set to Open.

I called for heat and I get 24 V between terminals 1 and 2 on the Taco indicating it is receiving power to open. But the boiler never fires indicating the end switch is not working. I register 24 v between 1 and 2 and also 24 v between 2 and 3. The head gets really hot. The voltage does not drop to zero on 2+3 and accordingly the boiler doesn't fire. My guess is the end switch is kaput!. The end switch is part of the power head, so that if I buy a new power head this should hopefully get the boiler to fire on zone 1, correct?
 
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Old 12-10-12, 09:50 AM
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My guess is the end switch is kaput!. The end switch is part of the power head, so that if I buy a new power head this should hopefully get the boiler to fire on zone 1, correct?
Sounds like it... but it might not be the endswitch. The valve itself might simply be not opening. Yes, the heating element in the 'heat motor' is working, getting hot, but it is possible still that the valve itself is not even opening.

In any case, replacing the head should solve either or both failure modes.
 
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