Home Furnace Monitoring System

We moved into our retirement home in July of 2006 outside the Western Slope town of Austin, Colorado.  The house is a split level, wood sided, shake shingled roofed house built in 1971.  It is located on a small round hill that overlooks the mountains in all directions except toward the West.  We fell in love with this unique place and have been working on it since then.

One area that has become a real concern is the cost of heating this 2,700 sq. ft. home.  It was originally built with electric baseboard heat, which, at time, was the most economical way to go.  Back in the 70's the local electric company offered a discounted service for home electric heating.  Some years later, they did away with this discount and immediately turned electric heating into a very expensive alternative.  Eleven years ago the then owners had a three zone baseboard hot water system installed with three zones.  Since natural gas service would be very expensive to be run 1/3rd of a mile up the hill, they settled on LP gas to be used that was equipped with a mini-therm hydronic boiler.  The unit is rated at 244,000 Btu's.  The system basically heats water to a pre-determined temperature and a water pump is activated that pumps water through 1" copper tubing to the active zone(s) where the water flows along a baseboard heating unit.  Air circulates past the unit's fins and is warmed.  This is a very comfortable heating system.  There is very little moving air and the entire room(s) are heated to the level set by the thermostat in the main room of the zone. 

The local LP supplier installed a 500 gallon tank behind the house and will drive over with a tank truck once a month to check/refill the tank.  Our first exposure to this company was in late July on 2006 and a new contract for the tank and service and a suggested pre-purchase of a full tank for several cents off the cost per gallon.  We wrote a check for over $800 for a full tank not knowing how long it would last through the winter.  In October, we were visited by the truck which topped off the tank with another 152 gallons for $288!  We were engaged with a variety of house projects at the time and did not focus on this surprise.

The Problem

From October 2006 through March of 2007, through December of 2006  we paid a total of $2,175.  At the end of the winter of 2007, we paid $1,787.08.  The cost per gallon during this period ranged around $1.89 to $2.50 per gallon of LP.  This year, the cost will probably creep toward $3.00.  What makes this scary is that during this time, I installed auto setback thermostats in the upstairs area and the downstairs den/bedroom was set as low as it would go.  During the winter months, the temperatures will drop into the low teens and only briefly rise above freezing most days.  The winter winds can suck the heat out of the house very quickly.  We keep the temperature around 62 degrees in the morning and evening hours and around 58 degrees at night or during the daytime hours.   Our house is always chilly, ask our friends and visitors!  With LP going higher, it is going to get much more expensive to live in this home we love.

Trying to sort out the overall costs of heating the house gets a bit tricky.  I needed to try and come to grips with what it costs when the actual monthly costs between electric and LP are different.  With electric, we pay each month for actual usage.  With LP, the tank gets filled when it gets low.  So, to get my hands around this, I took the LP costs for the winter months between October 2006 and March 2007 and divided it by six for the average monthly cost or, $362.62.  I did the same for 2007-2008 winter months or $297.85.  I then added these average to the monthly electric charge.  The graph clearly shows our total energy costs for these months.  Surprising!

An Opportunity

In early May of 2008, we received a flyer from our local electric company, DMEA, that discussed a new type of service they are offering called "time of use" rates.  This type of service has been around for a long time but was new to this area.  With a new dual-set meter, they can track eclectic usage during different times of the day.  The normal kil-a-watt rate is $.09703/KWH.  The new rate structure offers a rate of $.03843/KWH for the off-peak usage and $.15375/KWH during peak usage.  Obviously there is a dramatic difference between the two rates.  If one can channel their electric consumption into the off peak, serious savings can occur.  So, as an example, if you were to use an electric heater (say 1,600 watt rating) for six hours the normal cost would be $.93.  With TOU service, this would cost $1.48 during peak but only $.368 during off-peak, a dramatic savings.  We decided to change over and, for that month, we saw a reduction of about 30% over what we paid for electricity during the same period the previous year.  I took daily readings from the meter and plotted the use and costs. 

It becomes obvious that significant savings are available if you work on shifting usage to the off-peak times.

So, clearly we could use a lot more electricity to offset the cost of LP for heating.

The Complexity

To tie all this together to save some serous utility costs without freezing to death, I needed to do some things.  First, I needed to know when the existing heating system turned on and off.  It is so quiet that most of the time I am not aware that it is on.  I needed some way to track the exact usage over time because the only other method of watching LP consumption, beyond getting the monthly bill, was to inspect the gauge on the top of the tank.  This gauge has not worked since we moved into the house.  They installed a new tank with an operating gauge but it is so small that is simply impossible to track consumption beyond a very gross measurement.

What I wanted was a way to track exactly how much LP is being used on an hour/daily basis.  This furnace is rated at 244,000 Btu as mentioned earlier which translates to about 2.67 gallons of LP per hour!  That is $6.70 per hour at $2.50/gallon! At that rate of consumption, it is really important to know when it is running and for how long.  Once we knew what was actually costing on an hour/daily basis, we could start using alternative methods of heating.   To reach an optimum break point between LP and electricity, I needed to know how much and when.

Hardware and Software

I am a retired senior manager but, as a hobby, I have dabbled in both electronics and software programming for years.  It seemed to me that developing a computer program that would run on any PC (not dedicated) to track the furnace would be straight forward.  A sensor would be needed to determine the state of the furnace and I decided that I could slip a photo cell next to an little LED light that turns on when the furnace fires up and stays on until it shuts down. I used a photo cell but a temperature sensor would work as well.

The tricky part was developing an interface with the computer.  It needed to be simple and universal.  I chose the parallel printer port since virtually all PCs have one.  Most printers these days use a USB port.  A few spare parts were used to connect to one of the control lines of this port.  Anytime the furnace turned on, this port would trigger.

I used and old friend, Turbo Basic, to write the code.  I used this same package over 15 years ago on another house monitoring system.  Once the code is completed, it can be compiled and then run on any DOS PC.  I have and old Compaq laptop that I don't use anymore which will be dedicated to the project.  The program, when run,asks for some simple setup values and file names.  Once run, as long as nothing needs to be changed, you don't have to fiddle with setup.  The program is continuously checking the port to see if the furnace has turned on.  When it does, the program notes the date and time and once it shuts off, give a shut off time.  The number of seconds the furnace has run is then plotted on a simple graph at the bottom of the screen.

Each time the furnace comes on-goes off, there is a record stored in a data file in the computer.  It is a simple text file that can be copied and pasted into a spreadsheet for further analysis.  The chart below shows the raw data with the actual seconds per cycle in the far right column.  The daily summaries are in the right set of columns with cumulative costs.

Raw data



















 $    2.69

 $    2.69






 $    2.39

 $    5.07






 $   12.84

 $   17.91






 $   13.95

 $   31.86






 $   12.08

 $   43.95








It was surprising how fast the cost of LP consumption rises.  These readings were the first set of test readings I made without changing our thermostats.  In six days we burned about $45 worth of LP.  Of interest as well are the blank columns on the screen and note the "0" value in the first line of the raw data.  This tells me that the furnace tried to start and shut down.  A second later, it tried again and started.  This might be an indication of a problem with my furnace which I would otherwise not be unaware of.

Putting all this together

Now that I know exactly when and how long the furnace is on and I know how much it will cost to heat with either LP or electricity, I can determine breakpoints for how much electricity I can consume heating the house before it exceeds the equivalent amount of LP gas.  The cost of a KWH of electrify off-peak is $.034 whereas the equivalent cost of a KWH of LP is approximately $.09, or about triple.  It is more difficult to determine these cost points in the overall process of heating 2,700 sq.ft.  The furnace heats one or more of three zones whereas an electric heater is only heating the specific room it is place in.  Direct comparisons become difficult.  Dynamically, it will get down to heating individual rooms separately until the outside temperature becomes so low that they will not keep up.  At some point the furnace will be necessary to offset this and bring a zone up to a certain point.  This whole process will take trial and error to determine the right mix of heating processes.  But, in the final analysis, combining electric heat with LP will clearly result in a lower heating cost for us over time.  The beauty of this system is there are no capital costs involved, just a little ingenuity.

                Livingroom                                       Kitchen                                              Bedroom

The three heaters above provide enough heat so far.  As it gets colder for longer periods, head from the furnace will be necessary.

Initial Results

Since November 8th, we have used timers to turn on and off  these heaters (1,600 watts).  They only operate during the 'off-peak' time.  The temperatures have dropped lower (below 25 degrees) at night for the past five nights.  Today, November 22th, the LP furnace has not turned on once since November 9th!  As the afternoon temperatures drop (daily highs have averaged around 55 degrees) we may have to use the furnace some.  I will update this site as we go through the winter months.  But, it is clear to me that we can look forward to some serious reduction in LP consumption this winter!  Our cost of electricity during this period has averaged $3.39/day!

There is a Bonus

Those folks who know me know that such a set up will be inevitably expanded to do other things as well.  Since we live on a hill outside of town and are relatively remote, I have been interested in some method of providing a reliable method of knowing if we have company driving or walking up our drive.  As the picture to the left shows, we have about a 1/3 of a mile to the paved highway. If we are inside, we are not aware of someone until we hear a knock on the front door.  After living back East for twenty years, we are concerned about not being aware. 

With some additional programming and an additional port on the parallel interface, and two wireless driveway IR monitors, I can monitor comings and goings.  The IR monitors were modified to bring out a relay contact which is made when the monitors trigger. I installed two units because they tend to false trigger when the wind blows.  Now, they both have to trigger at the same time to activate the system.  These are inexpensive units I purchased at Harbor Freight. 

Once triggered, the program date/time stamps the event and also flashes lights on a star that hangs on an observation deck in front of the house.  Anyone walking or driving up will see this star flash three times indicating that their presence is known! Inside, we will be aware of their presence with a flashing LED and a small 'chirp' sound in the living room and master bedroom.

In addition to these features, I have also included an alarm that will trigger if several different things were to happen: sub-basement flooding, furnace overheating, etc.  If one of these alarms were to trigger, a much louder horn would be triggered to get our instant attention.  I will probably have the star out in front do something to signal our neighbors down the road as well.







Enhancements to Come

The obvious first enhancement to the furnace monitoring is to provide a wireless link between the furnace and the computer that is monitoring it.  At this point, a two wire line connects the two points.  This restricts where the computer sits.

Since my initial writing, I have installed a wireless sensor pictured to the left.  The top wire is for power and the bottom wire goes to the photo sensor on the furnace.  A receive module is connected to the parallel port.  It works.  The TX/RX has a range of about 40 feet.  A longer antenna should increase this.






See new schematic using a PICAXE that replaces the PC interface.



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