I want to use an Arduino to datalog the gas usage of my furnace. This isn't really an arduino question though, its more related to finding the best sensor/electronics to interface with the furnace.

I have an IBC DC 33-160 boiler that burns propane. The boiler can ramp up or down between 33k and 160k BTUs depending on heating requirements of the house.

Because of this ramp up/down I can't simply monitor the thermostat contact closure to determine gas usage.

A gas meter is a potential solution, but that's quite expensive and would be quite cumbersome to install.

What I would like to try and do is monitor the air flow on the boiler's fresh air intake, which is a 1.5" PVC pipe. If I know the airflow, it should be relatively easy to calculate the gas consumption.

The question is what kind of sensor would be best for this application? There are three options that I've found while searching:

  1. Mass Air Flow - a powered wire element is put into the air flow and depending on the resistance of the wire, you can determine the airflow. MAFs are commonly used by car ECUs to meter the air and spray the appropriate amount of fuel. The problem with this one is that most MAFs are 12v for auto applications and I'm not sure how I would calibrate it to a known value.
  2. Pitot Tube - these are used to measure air speed and I found that they are also commonly used in HVAC applications to measure air flow - I just don't know if its sensitive/accurate enough to calculate gas consumption.
  3. Ultra Sonic - apparently you can determine air flow using ultrasonic sensors aimed at an angle at each other in a tube - I've found some articles about it, but this option seems like the most complicated of the three
  • \$\begingroup\$ Option 4. Monitor the gas meter. This would be a good option if there is only one gas appliance in your premises. I fitted an industrial photo-sensor to monitor my rotating electricity meter. \$\endgroup\$ – Transistor Jan 10 at 16:22
  • \$\begingroup\$ "The boiler can ramp up or down between 33k and 160k BTUs depending on heating requirements of the house." Can you monitor the heat requests and summarize those over time? \$\endgroup\$ – CrossRoads Jan 10 at 16:24
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    \$\begingroup\$ Installations of these types of boilers are covered by code, including the intake venting. I'm pretty sure you can't put anything directly in the flow path and still be within code. You might try monitoring your propane - either by weighing the tank or using an stick-on ultrasonic level detector. \$\endgroup\$ – John Birckhead Jan 10 at 19:18
  • \$\begingroup\$ @JohnBirckhead I have two 420lb tanks that are 60' away from the building in the woods. Weighing them isn't an option, nor is putting a powered device near them. \$\endgroup\$ – Paul Wieland Jan 10 at 19:30
  • \$\begingroup\$ @CrossRoads unfortunately no. This is a hydronic in floor radiant heat system. The boiler uses a PID loop to try and hit its set point. The returning water temp will vary depending on how cold the floor is. \$\endgroup\$ – Paul Wieland Jan 10 at 19:33

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