I want to keep track of when my furnace is on, with an eye to reducing how much energy I use to heat my house.
I could compare it with weather data (temperature, wind speed, precipitation).
I could see what it saves to turn the heat down when we're out.
I could tell my kids exactly how much it costs when they leave the front door open.
While this won't specifically isolate your furnace from the rest of your energy usage, I'd recommend getting a Blue Line PowerCost Monitor (or the Black & Decker branded version, which is cheaper) their WiFi Gateway, and a free Microsoft Hohm account.
Current Amazon links and prices:
That will give you a display that shows electricity used (and cost, if you enter the rates) and let you view some nice charts of usage over time (including temperature for your zip code) on the Microsoft Hohm site.
Here are some graphs from my account to show what I mean...
The 6-hour usage graph shows 'humps' where the (electric) fan for our (gas) furnace is blowing. Other 'humps' likely represent our refrigerator. The only real way to identify which is which is to turn off one or the other for a period of time and see how the graph changes. For the record, I haven't yet installed a programmable thermostat so our furnace will try to maintain ~68F all day and night.
The daily usage graph shows us returning home around 6:30 last night, that I was up until about 1:30 this morning, and that we were up and moving about this morning from 6:30-9:30.
The monthly usage graph shows our usage each day and what the local temperature was (which isn't available for the most recent couple days yet). You can see how the temperature affects our energy usage pretty clearly. Obviously the chart shows that our usage was lower both of the past two weekends (24-26th and 30th-1st), but you can't tell from the chart that this was because we were out of town those days. Had we been home, our usage would probably be higher than the normal weekday usage.
I'm sure there's plenty of energy trimming we can do, as we've just gotten started with this. But for only $150 invested (I got the Gateway for $103 in November), it's a pretty easy solution to help save in the long run.
The installation was easy for both the Monitor (on the electric meter outside our house) and the Gateway (setup my WiFi network info via USB cable, then reposition Gateway unit within range of both Monitor and our WiFi router and an electrical outlet).
I have an ancient oil-fired steam boiler with a "tankless" hot water heater. I built an Arduino-based board that connects in parallel to the thermostat wires at the furnace. It uses a MID400 AC optocoupler to detect when the thermostat is calling for heat (24VAC when not calling for heat, 0VAC when it is), and then sends that to a computer via an XBee module.
From that you can keep track of how long the furnace runs. It's a very simple system with several shortcomings: It doesn't make a distinction between when the main zone of the house is calling for heat vs when hot water is called for, and can't tell when heat's being called for, but it can tell you when the low water or high temperature cut-outs have kicked in.
Not perfect, but it should give you some idea of your energy consumption.
You could mount a wind speed logger in your ductwork or in front of your air intake vent. It should have negligible drag effects on airflow through the system. I'm not sure how accurate the results would be though. The air movement from your furnace running is going to be a lot less than outside wind levels, which is what most wind speed loggers are actually designed for.
You can pick one up on Amazon for about $100.
Or you could go the direct approach with a breaker-installed power use monitor. This option's about twice the price, but monitors your whole house. Unfortunately, this method won't tell you exactly when your furnace comes on, although you should be able to figure it out, since it gives you a time history of power usage. Just note when you get a big spike, and then a big drop and match it to when your furnace turns on and off. Then look for that same magnitude spike in later data, without bothering to manually keep track of furnace cycling.
All furnaces use 24 volt control systems. If you want to know the run time of it simply install a Hobbs Meter.
Jay, if you need to monitor just the furnace (what kind of furnace), a very simple Amprobe chart recorder will do the job by monitoring the electrical inputs to the burner or pumps without any invasive wiring or computer interface. Old fashioned, but used in industrial applications for decades.
Its a pricey solution, but get a Nest thermostat. It will track that and send you an email every month on how much the system has run so you can track it and the costs associated. I just installed it, took less than 20 minutes. The feature I really like is that the system is remotely accessible. I travel extensively for work and will put it in away mode (drops/raises temperature while no one is there) when I leave, but turn it back on the day I will return. When I get back, my place will be comfortable.
The Hohm power monitoring service used to be a great way to keep tabs on energy consumption (check out BQ's awesome answer), but in mid 2011 Microsoft discontinued it just as Google discontinued its competing service, Powermeter.
But while the tech giants seem to have abandoned home energy monitoring, several smaller players now offer similar services:
myEragy - A free web-based energy consumption dashboard that provides subscribers with real time, historical and projected info and sends alerts via email or SMS when you go overbudget or a specific circuit uses too much energy. myEragy supports several electricity monitors, including Blueline PowerCost Monitor with WiFi, TED 5000 and eGauge.
PlotWatt - Currently in beta, PlotWatt is a free service that plots energy usage in a user-friendly way, and according to the FAQ, tracks individual appliances using "algorithms." Suspicious, certainly, but promising. The service is compatible with TED and WattVisions monitors.
There are also more integrated options out there, such as Opower & Honeywell's thermostat product, which lets you adjust and monitor your thermostat from anywhere, and MyEnergy, which lets customers track electric, gas and water.
It's an exciting space out there with a lot of promising options. This is just a start.
Came late to the party, but just wanted to add my method (which is mostly DIY) - I have a wireless Arduino that records the temperature near a vent, sends it to the computer where it's saved in a database. There I can graph it, and (in the "near" future) be able to calculate the on/off times.
