# Door sensors to turn off heater when doors open (wiring)



## hvactech126 (Nov 11, 2010)

Wire the sensors in series with the W circuit


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## westbank (May 4, 2010)

hvactech126 said:


> Wire the sensors in series with the W circuit


Thanks for the quick response. So *both* wires from the last sensor should be wired to the W terminal on the thermostat. 

Best technique would be to put both sensor wires into a marrette connector along with another wire that would go into the W terminal of the thermostat ? Am I right ?


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## hvactech126 (Nov 11, 2010)

each sensor has 2 wires correct? If so, the wires would break the W circuit.


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## westbank (May 4, 2010)

hvactech126 said:


> each sensor has 2 wires correct? If so, the wires would break the W circuit.


Yes, they have two wires.
Like this one


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## hvactech126 (Nov 11, 2010)

see my edited post #4


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## Bob Sanders (Nov 10, 2013)

You would install the switches in series with each other. This would allow either one or both opened doors to turn off the heater.

Disconnect the w wire from the thermostat and connect it to one of the wires on sensor 1. Take the other wire from that sensor 1 and connect it to a wire on sensor 2. Take the second wire from sensor 2 and connect it to the w contact on the thermostat.

I'm assuming these sensors are the normally open type? (They make contact when the magnet is near to it). This being the case then line the switch up with the magnet when the door is in the closed position.


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## westbank (May 4, 2010)

Thanks again ! With you wiring diagram, if only one door is open, will it shut off the heater ?


hvactech126 said:


> see my edited post #4


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## biggles (Jan 1, 2008)

switches need to be in series.... mount a utility box between the doors ceiling high. run a 2 wire bell stat wire to that utility box from the stat...run both switches to the box..connect 2 switch wires together wire nut(they are in series now)connect the remaining door switch wire to the bell stat wires "one each" wire nut....now at the stat remove the W wire ...nut it onto a bell wire and the other bell wire to the W terminal...your done


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## hvactech126 (Nov 11, 2010)

Taken from your diagram there was only 1 door/sensor... so add another in the same manner and it will work as you like.


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## Bob Sanders (Nov 10, 2013)

westbank said:


> Thanks again ! With you wiring diagram, if only one door is open, will it shut off the heater ?


Yes. One or the other, or both


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## westbank (May 4, 2010)

Thanks to everyone for your help.

My plan is to mount the thermostat on a single gang (utility) box so I would use the utility box to do all the wire connections inside.

Would it be possible to confirm if the diagram below is ok (please note that I didn't wire the C and R terminal in my diagram) ?


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## yuri (Nov 29, 2008)

Are these switches the same as they use for house alarm systems? Are they an actual switch (snap action switch) and will not reduce ANY voltage? If they are proximity sensors meant for alarms and drop any voltage to the W of the furnace then it can get damaged. I would want a switch that operates a relay (Honeywell R8222 D or K relay) that has a normally open contact and put your W wiring thru that contact.

Basically you get a extra 20 VA 24 volt transformer and run power to those sensors and operate the R8222D relay with them. run your W wire thru the normally open contacts on the relay and it is safe.


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## westbank (May 4, 2010)

*Yuri*
I was thinking about going with a garage door sensor like this one:
http://www.seco-larm.com/pdfs/PI-SM-226LR-3.pdf
It's considered a switch; only on and off are possible.




yuri said:


> Are these switches the same as they use for house alarm systems? Are they an actual switch (snap action switch) and will not reduce ANY voltage? If they are proximity sensors meant for alarms and drop any voltage to the W of the furnace then it can get damaged. I would want a switch that operates a relay (Honeywell R8222 D or K relay) that has a normally open contact and put your W wiring thru that contact.
> 
> Basically you get a extra 20 VA 24 volt transformer and run power to those sensors and operate the R8222D relay with them. run your W wire thru the normally open contacts on the relay and it is safe.


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## iamrfixit (Jan 30, 2011)

I did this in my shop years ago. 

I used a simple and cheap micro switch that has a short spring lever. The switch is mounted on a bracket fastened to the track and I fabricated a simple arm on the door to trip the switch. When the door is completely shut the normally open/common terminals close allowing the heater to run. I used the wire from these two terminals to interrupt the signal from the thermostat. It's mounted up high just below the curve track so it wouldn't get bumped. Decided to install this after I got home one morning from working the night shift to find my door standing open at -15. Installed almost 20 years ago and it still works perfectly.


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## yuri (Nov 29, 2008)

I am concerned that you have a proper strong quality switch/contacts. That one is rated for 3 W watts but I don't know the wattage of your circuit. Like iamr's method he used a actual switch which can carry some current w/o arcing etc. When you are using switches and components from alarm systems or garage door openers that are low voltage/low current that is not the same as what a furnace uses, there are safety issues. My system of using a R8222D relay (google it) uses a strong general purpose relay and I used it hundreds of times in the old days for millivolt systems to trigger them with modern 24 volt thermostats. You should be able to go to graingers and get that relay and a basic 120/24 volt 20 VA transformer and mount it in a box and screw the relay onto a beam beside it and run some wires. Use 18 gauge wire (LVT or bell wire and nothing smaller) HDepot has it.


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## westbank (May 4, 2010)

Thanks for the feedback.

I'm not an expert so getting your input is helping me a lot.
I have a relay with a built-in transformer between the thermostat and the heater. This one: http://www.aubetech.com/products/produitsDetails.php?noLangue=2&noProduit=42





yuri said:


> I am concerned that you have a proper strong quality switch/contacts. That one is rated for 3 W watts but I don't know the wattage of your circuit. Like iamr's method he used a actual switch which can carry some current w/o arcing etc. When you are using switches and components from alarm systems or garage door openers that are low voltage/low current that is not the same as what a furnace uses, there are safety issues. My system of using a R8222D relay (google it) uses a strong general purpose relay and I used it hundreds of times in the old days for millivolt systems to trigger them with modern 24 volt thermostats. You should be able to go to graingers and get that relay and a basic 120/24 volt 20 VA transformer and mount it in a box and screw the relay onto a beam beside it and run some wires. Use 18 gauge wire (LVT or bell wire and nothing smaller) HDepot has it.


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## yuri (Nov 29, 2008)

That relay is a high current relay to handle the 220 volt high current heater element. You need a different/additional relay to do the 24 volt control side.


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## westbank (May 4, 2010)

If I want a reliable solution and would like to avoid a relay on the low voltage side (for thermostat and door sensors) what are my options ?

Thanks again. Much appreciated.




yuri said:


> That relay is a high current relay to handle the 220 volt high current heater element. You need a different/additional relay to do the 24 volt control side.


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## yuri (Nov 29, 2008)

None that I know. 

Trained monkey:laughing:


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## westbank (May 4, 2010)

What if I get a magnetic door switch rated for 24V ?
The thermostat is 0.5A at 24V (12w)
The door sensors are 0.41A at 24V (9.84w)

This sensor is rated for 24V: http://www.elementalled.com/magnetic-drawer-switch.html


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## yuri (Nov 29, 2008)

Then they are 2-3 watts too small. If you go the cheap route then later damage some components you will be sorry. If you create a fire hazard you will even be more sorry. One of my customers had his garage catch on fire from a staple pinching a low voltage wire to a central vac system. Did a couple hundred thousand $$ in smoke damage to the house and he had to live in a hotel for 6 months. Safety comes first not saving a couple $$.


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## westbank (May 4, 2010)

Thanks again.

I didn’t know that a minor difference in wattage could cause a serious risk. 
I don’t have a budget and I’m looking for the best reliable option. Is there a compact 24v relay that could fit in a single gang box and work with two NC door magnetic sensors ?


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## yuri (Nov 29, 2008)

The R8222D relay has been around for over 30 years and is bombproof reliable. It is easy to mount to a piece of metal or wood. Put some metal over the wood if you want to be safer. After that whatever relay you choose is up to you. You get what you pay for $$ wise. I have no others to recommend or other ideas.

https://customer.honeywell.com/en-US/pages/product.aspx?cat=HonECC%20Catalog&pid=R8222D1014/U


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## westbank (May 4, 2010)

Thanks Yuri. I will read more about that relay and hopefully I will figure out how to wire the two doors sensors and thermostat into it.




yuri said:


> The R8222D relay has been around for over 30 years and is bombproof reliable. It is easy to mount to a piece of metal or wood. Put some metal over the wood if you want to be safer. After that whatever relay you choose is up to you. You get what you pay for $$ wise. I have no others to recommend or other ideas.
> 
> https://customer.honeywell.com/en-US/pages/product.aspx?cat=HonECC Catalog&pid=R8222D1014/U


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## yuri (Nov 29, 2008)

Pretty easy. R which is 24 volts hot from the transformer goes to one side of the door sensor and thru it and into the other sensor and thru it and feeds the 24 volt coil of the R8222D and then goes back to C on the transformer. W from the thermostat goes thru a normally open NO set of contacts on the relay and then to the heater relay. The R8222D comes with a wiring diagram. This way if the door sensors fail and give off low voltage all that can happen is the R8222 gets damaged not your heater.


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## yuri (Nov 29, 2008)

Put a 120 volt switch in line with the transformer and in the Summer shut it off when you don't need the heater and it will save wear and tear on the R8222.


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## westbank (May 4, 2010)

Thanks for the help.

The difference I have from your diagram is that my heater has no W terminal so that's why I need the 24V relay (with a built-in transformer) to control it. See my diagram below:












yuri said:


> Put a 120 volt switch in line with the transformer and in the Summer shut it off when you don't need the heater and it will save wear and tear on the R8222.


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## yuri (Nov 29, 2008)

You put the NO normally open contacts on the W wire between the heater and the relay. Red circle.


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## westbank (May 4, 2010)

Thanks again Yuri. Much appreciated.

So if I understand correctly, based on your last post I could install the door sensors (in series) on the W wire between the relay and the thermostat ? I dont need the additional Honeywell R8222 Relay ?


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## yuri (Nov 29, 2008)

NO. The R8222 relay is an isolating relay. The door sensors if they fail or provide low voltage can harm your expensive heater relay. The R8222 does half the job of the other relay and protects it. The R8222 is like a pawn in case something goes wrong with the door sensors. Save the King and sacrifice the pawn and it is a safer method of doing things.

TECHNICALLY you should not be doing any of this homemade wiring without an electrical permit. I have to protect my butt with this disclaimer. If the inspector approves it then go ahead, if not then don't.


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## westbank (May 4, 2010)

Thanks for the additional details and for your help. It was really appreciated.


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## yuri (Nov 29, 2008)

Glad to help but reread my post as I added to it.


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