HVAC Flow Chart


Active Member
Hey all,

I put together a flowchart outlining how I’d like to program an Elk control panel to control an HVAC system.

The system, as it stands now, will consist of an Elk M1EZ8, an RCS TR16 thermostat, automated ceiling vents and remote temp sensors in each zone.

The normal state of the vents will be in the open position when the HVAC is off and closing the zones that don't need heating or cooling when the HVAC comes on.

If you wouldn't mind taking a look at the attached pdf and give me some feedback I would appreciate it.

As always, thanks guys.


  • HVAC_Flow_Chart.pdf
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Well here's what I can see:

Every 7 minutes you will be sending actuation commands to open vents and set setpoints even though the settings will most likely already be correct. This may or not be an issue. I try to program event driven operations because it reduces traffic. In your case, operations that would change a setpoint or vent condition would set a "changed" flag. then your 7 minute cycle would replace the set operation with an interrogate of the changed flag. If yes, then do the operation and reset the flag.

My system is mostly event driven. My 7 minute loop equivalent is a 1 hour trigger that interrogates thermostats to insure they're within setpoint tolerances. An out of tolerance situation indicates that a setpoint event was missed (rarely happens even with X10) and invokes a correction program. However it depends on thermostat devices that can report high or low setpoint events.

Your system may "jitter" too during those times of year where days can be cold as well as hot such as spring or fall. My system has master flags called "heating mode" and "AC mode" which are set when a 3 way when a master toggle is manually actuated (the third postion sets both to "off"). When in AC mode, all system requested heating requests are ignored and vice versa. That way, I can manually correct for "jitters" where the system is using AC to bring down a system heat related issue or vice versa.
Be aware that unless your system was set up to use dampers, you could harm it by closing down too many dampers. If airflow through the system is reduced too much, the heat exchanger on your furnace may overheat and crack.

Thanks for the replies guys.


The reason for the 7 minute check was because I was only going to have a single thermostat and was planning on using a temp sensor for a second zone (upstairs and downstairs). What I've realized is that I can use a second TR16 keypad upstairs by wiring through a return vent.

Because I'll be able to use 2 thermostats and, if I understand the documentation correctly, the thermostats will announce when the heating/AC is kicking on so I won't need to poll them and will instead be using a setup more like you described.


Thanks for your concern. I have only 9 vents in my home, 4 upstairs and 5 downstairs and I'm only planning on 2 zones, upstairs and downstairs. 1 vent upstairs and 1 vent downstairs, 1 in each in the bathrooms, will always be open. The rule that I keep running into (and has been pointed out to me by folks on this board) is that you don't want to run your system with more than 50% of your vents closed. With the way I'm planning on working this there's only 3 scenarios: 5 open, 6 open, or 9 open. I should be able to avoid overheating and over-pressurizing the system this way.

I gotta tell ya', I tried doing the balloon tied to a string trick to blow through the venting and it didn't go as smoothly as I had hoped. I bought some small water balloons from Target (because I have small venting) but they're too small to get pushed very far. I think I'm going to need to rent a tank of helium to blow them up with and see if that doesn't work a bit better next time.