How can I track my forced air furnace's on/off cycles automatically?

I’m trying to analyze my home energy use and one thing I want to know is how much time my hot air furnace is in use - how much time it spends heating/blowing air through the house. I can sit with a stop watch every day, of course, and that could be my life’s work this winter. Or, if I could get a way to do it automatically via the SD, I could do it that way. Anyone have any ideas on a relatively cheap and easy method I could use? Thanks, Dopers.

a person skilled in electronics and microcontrollers could build a device to do that. though i don’t think that would be of much value. compare your fuel cost to heating degree days.

Google “Data Logger”

Why not track it through your electric/ gas utility?

I think the nest thermostat can do what you want. (A friend got one and is enthralled)

You may be able to wire in clock with a dial (as opposed to a digital one) to the furnace motor power. Hopefully you could get one with a 24 hour cycle or one that includes the day or date. It would only run when power is applied.

It looks like a very nice programmable thermostat with a function that might do what I’m looking for, for about $250. I have a nice programmable thermostat, so maybe a data logger is what I’m after. Thanks.

I don’t think that will get you the data you want, though it cold save you money which sounds better then just knowing how much you are spending.

I have one that allows me to set and program it over the internet (which it appears like the nest does too) and like it a lot (cost about $100 from either Home Depot or Lowes ). When I leave I can remotely set it to a away setting and have it warm up the house as I am on my way home. Having a variable schedule this seems better then set times home and away.

Ultimately, I want to know how much it costs to run the furnace and to assess the difference that the outside temperature and the indoor setting makes in the frequency of cycling. We lose tons of heat through the walls and I’m trying to get a handle on the overall efficiency of settings, while contemplating the use of space heaters in different rooms. I’m hoping to get a better understanding of how much I could save by setting the thermostat higher or lower, and if it’s worth it to do that (given that it will take a longer time to get the house up to decent temperature if I set it at, say, zero during the day when no one’s here).

I have a 15 year old Honeywell programmable thermostat that keeps track of cumulative run time. I just checked and the current price for the Honeywell replacement, in Canada, is about $50.

You could simply plug a standard electric (not electronic) clock into the same feed the blower fan runs on. Reset it to 12 and read the hours elapsed each day. If you are handy, you can get an IO card for your computer and connect it to the thermostat. Then use logging software to track the info.

You can use a device called “The Energy Detective” I did exactly what you want to do. I now know what the heating cost versus outdoor temperature curve looks like for my house along with the energy use of all the other electric appliances. Very interesting to someone nerdy like me or baffling to someone who isn’t

You might rig up a simple switch attached to a piece of paper positioned by a vent, so when the furnace is blowing it turns on the switch. The trick is to track it; the real stupid way is to videotape it with the clock on so your camera tells you time on and off.

There are plenty of data acquisition modules for PC’s to read digital (on-off) or analog events, but they are rather specialty items. For example, this EL-USB-5 Event, State, and Count Data Logger looks like you could hook it to a wind switch; or just stick a temperature module EL-USB-1 EasyLog Temperature Data Logger by the air vent output and measure temperature, assuming hot air indicates furnace is running. Not clear what the software is for this, but I assume you can get a valid timeline.

If all you need to know is the total time the furnace is on, then a simple hour meter like those in this site will do: Hour Meters

These meters are routinely used in furnaces and boilers so any shop that deals with central heating products will carry them.