How-To Control your furnace using your Elk:
by Squiddy
I posted a How-To monitor the status of your furnace and briefly mentioned that I had run some extra pairs into the furnace to be used for control from the Elk. I had a request for more details on this project so I thought I would write something up for this as well.
What I want to be able to do here is control the fan and the heat for my furnace from my Elk but at the same time be able to revert back to old fashioned thermostat control if the the automation panel goes down or if I'm not home and my fiance can't get it working.
Remember again that you should only use this as a guide. I cannot be responsible for any problems you cause while following these instructions. I recommend that you write some backup logic that looks at your furnace status input and if it runs for more than x minutes, do something and send an alert to yourself. You could install another normally open relay on the 24VAC power line coming from the furnace and shut that power off.
N/C Relay contacts vs. N/O Relay contacts:
Below you will see that I have got one relay with normally closed contacts and two relays with normally open contacts. There is a reason for this. In the event of an automation panel power failure, you want to think about what your controls (outputs) are doing. It wouldn't be very good if you shut your Elk down, shutting down control power to your "Elk Call for Heat" relay and have your furnace heat come on. This is why you want to use a normally open relay for the fan and heat controls. When a normally open relay loses power, the contacts "Open", breaking the Call for Heat signal back to the furnace.
The same goes for your Elk/Thermostat control line. You will want to use a normally closed relay here so that if you lose power to your control relay, control automatically reverts back to the thermostat upstairs, leaving you with control over your furnace.
Materials Required:
* Enough wire to give you 3 pairs of 300V or 600V rated, 105 degree C (for furnace use) wire to go from the furnace to your automation panel
* Enough single pair (300V or 600V AND 105 degree C rated) wire to go from the furnace to your automation panel
-- Wire in the US will probably be rated in degrees F
-- Check with local regulations regarding of wire rating for use in furnaces
* Marrettes, tie wraps, tape
* One relay with normally closed contacts (could use Elk-912)
* Two relays with normally open contacts (could use two Elk-912's)
Have a look at my amazing drawing above. The top half shows the wiring before I touched it from the Thermostat to the Furnace. The bottom half shows the modifications I made.
Take one pair of wires and connect it up to the 24VAC and COMMON at the furnace end. Run this back to your panel. You will use this power to send control signals back to the furnace. You don't really need to take the COMMON wire back to your panel but I did just in case. Take another pair of wires and connect one wire to the "Call For Heat" terminal on the furnace, and the other wire to the "Call For Fan" terminal. Label both wires accordingly. You will have to check your furnace for the location of these two terminals. Take the "Call For Heat" wire (coming from the thermostat) off of the furnace end and marrette it on to one of the wires in the remaining pair from your automation panel.
At your panel, wire three outputs up to your three relays. Label these three outputs as "Call for Heat", "Call for Fan" and "Elk/Thermostat Control" (or however you would like to label them :angry
. Take the 24VAC hot wire and connect it up to the COMMON terminal of your "Call for Heat" relay and your "Call for Fan" relay. If you are using Elk-912's, the terminal is labeled COM on the board. Next, take the wire connected up to your furnace coming back to your panel you labeled "Call for Heat" and connect it to the N/O pin of your "Call for Heat" relay AND to the N/C pin of your "Elk/Thermostat Control" relay. Then, take the wire connected up to your furnace coming back to your panel you labeled "Call for Fan" and connect it to the N/O pin of your "Call for Fan" relay. Finally take the wire you marretted onto the "Call for Heat" wire coming from your thermostat, and connect it to the COMMON pin of your "Elk/Thermostat Control" relay.
The way this will work is as follows:
When power is OFF to your "Elk/Thermostat Control" output, your thermostat will have the ability to control your furnace heat. When the power is ON to this output, signals coming from your thermostat will not make it to the furnace.
If you turn ON your "Call for Heat" output, the furnace heat will come on. When you turn OFF this output, your furnace heat will turn off and the furnace fan will blow the hot air around until the temperature drops (to a point set up in the furnace control board).
You can then turn the "Call for Fan" output ON and OFF to turn the furnace fan ON and OFF. This is usually used in the summer months to ventilate the house.
Having the "Call for Heat" output ON and the "Elk/Thermostat Control" output OFF will not hurt anything since the 24VAC source is the same and they will both end up being referenced to the same COMMON point. You will never need to have it like this because you normally either want control from your Elk OR control from your thermostat but I just wanted to make a note of it in case you were wondering.
by Squiddy
I posted a How-To monitor the status of your furnace and briefly mentioned that I had run some extra pairs into the furnace to be used for control from the Elk. I had a request for more details on this project so I thought I would write something up for this as well.
What I want to be able to do here is control the fan and the heat for my furnace from my Elk but at the same time be able to revert back to old fashioned thermostat control if the the automation panel goes down or if I'm not home and my fiance can't get it working.
Remember again that you should only use this as a guide. I cannot be responsible for any problems you cause while following these instructions. I recommend that you write some backup logic that looks at your furnace status input and if it runs for more than x minutes, do something and send an alert to yourself. You could install another normally open relay on the 24VAC power line coming from the furnace and shut that power off.
N/C Relay contacts vs. N/O Relay contacts:
Below you will see that I have got one relay with normally closed contacts and two relays with normally open contacts. There is a reason for this. In the event of an automation panel power failure, you want to think about what your controls (outputs) are doing. It wouldn't be very good if you shut your Elk down, shutting down control power to your "Elk Call for Heat" relay and have your furnace heat come on. This is why you want to use a normally open relay for the fan and heat controls. When a normally open relay loses power, the contacts "Open", breaking the Call for Heat signal back to the furnace.
The same goes for your Elk/Thermostat control line. You will want to use a normally closed relay here so that if you lose power to your control relay, control automatically reverts back to the thermostat upstairs, leaving you with control over your furnace.
Materials Required:
* Enough wire to give you 3 pairs of 300V or 600V rated, 105 degree C (for furnace use) wire to go from the furnace to your automation panel
* Enough single pair (300V or 600V AND 105 degree C rated) wire to go from the furnace to your automation panel
-- Wire in the US will probably be rated in degrees F
-- Check with local regulations regarding of wire rating for use in furnaces
* Marrettes, tie wraps, tape
* One relay with normally closed contacts (could use Elk-912)
* Two relays with normally open contacts (could use two Elk-912's)
Have a look at my amazing drawing above. The top half shows the wiring before I touched it from the Thermostat to the Furnace. The bottom half shows the modifications I made.
Take one pair of wires and connect it up to the 24VAC and COMMON at the furnace end. Run this back to your panel. You will use this power to send control signals back to the furnace. You don't really need to take the COMMON wire back to your panel but I did just in case. Take another pair of wires and connect one wire to the "Call For Heat" terminal on the furnace, and the other wire to the "Call For Fan" terminal. Label both wires accordingly. You will have to check your furnace for the location of these two terminals. Take the "Call For Heat" wire (coming from the thermostat) off of the furnace end and marrette it on to one of the wires in the remaining pair from your automation panel.
At your panel, wire three outputs up to your three relays. Label these three outputs as "Call for Heat", "Call for Fan" and "Elk/Thermostat Control" (or however you would like to label them :angry
. Take the 24VAC hot wire and connect it up to the COMMON terminal of your "Call for Heat" relay and your "Call for Fan" relay. If you are using Elk-912's, the terminal is labeled COM on the board. Next, take the wire connected up to your furnace coming back to your panel you labeled "Call for Heat" and connect it to the N/O pin of your "Call for Heat" relay AND to the N/C pin of your "Elk/Thermostat Control" relay. Then, take the wire connected up to your furnace coming back to your panel you labeled "Call for Fan" and connect it to the N/O pin of your "Call for Fan" relay. Finally take the wire you marretted onto the "Call for Heat" wire coming from your thermostat, and connect it to the COMMON pin of your "Elk/Thermostat Control" relay. The way this will work is as follows:
When power is OFF to your "Elk/Thermostat Control" output, your thermostat will have the ability to control your furnace heat. When the power is ON to this output, signals coming from your thermostat will not make it to the furnace.
If you turn ON your "Call for Heat" output, the furnace heat will come on. When you turn OFF this output, your furnace heat will turn off and the furnace fan will blow the hot air around until the temperature drops (to a point set up in the furnace control board).
You can then turn the "Call for Fan" output ON and OFF to turn the furnace fan ON and OFF. This is usually used in the summer months to ventilate the house.
Having the "Call for Heat" output ON and the "Elk/Thermostat Control" output OFF will not hurt anything since the 24VAC source is the same and they will both end up being referenced to the same COMMON point. You will never need to have it like this because you normally either want control from your Elk OR control from your thermostat but I just wanted to make a note of it in case you were wondering.
