What one gentleman in northern Minnesota did to increase the amount of heat his woodstove put into his living space
I have two weaknesses in my ability to roll up the sidewalk and tell folks to get off my lawn.
One of my shortcomings involves water. The water table is 45 feet below the surface so I need some kind of submersible pump should the grid go down. Suction can pull pure water up about 30 feet and water with dissolved gasses about twenty feet.
The other shortcoming involves heat. The average nightly low for January is 20F and the average high is 30F but there have been weeks when a Polar Vortex kept the windchill below -20F for the entire week.
The fireplace insert
I have a fireplace insert. When I have electricity it can put between 15,000 and 20,000 BTU per hour into the house. Not enough to run around nekkid when it is -20F but enough to keep the pipes from freezing.
The problem is that the blower pulls 140 Watts of 120V alternating current. No electricity means almost no heat out of the unit AND not running the fan will overheat the firebox and damage can result.
Being the smart fellow that I am, I bought a small, very efficient "inverter" generator. At low load, defined by the manufacturer as 400W draw, it can run 11 hours on a gallon of gas.
Sounds great, right?
One gallon of gas has about 115,000 BTU of heat-energy. Running the fireplace insert for 11 hours at 15k BTUs will net me 165,000 BTUs. Not quite the slam-dunk I was hoping for.
Battery assist
At 400 Watts, there is enough power (on paper) to run the fan and charge a glass-mat, deep-cycle battery. A battery that holds 1200 Watt-hours costs about $250 and has a five-to-ten year life.
In our perfect, theoretical world at 400 Watts the generator could run the fan and fully charge the battery in about five hours. That would be fifteen hours of heat (15 times 15k BTU/hr equals 225k BTU) at a cost of 57k BTU. In round numbers, that is 4 BTU of heat for every BTU of gasoline burned.
Solar + batteries + genny back-up
Stand-alone solar without batteries is non-starter in the north. Days are short. Nights are long and cold.
1200 Watts of solar capacity might provide enough energy to run the fan on the fireplace insert for 16 hours most days. Sixteen hours being the amount of time there is a responsible adult awake to feed the fire.
The smart money would have at least two deep-cycle batteries. They really do not like to be fully drained. Two batteries cycling in the top-half of their capacity will last far longer than one battery being 100 percent drained daily.
And there will be weeks when the clouds shut down the solar. That is when the generator comes into play.
The fine print
Lots of detail about inverters and such were left out. Batteries are Direct Current storage devices.
Universal motors can miraculously run on either AC or DC current as long as the voltage is appropriate. Unfortunately, that means a boatload of 12V batteries (for DC mode) or an inverter.
Why not a stand-alone woodstove?
Great question.
The ever-wise and ravishingly beautiful Mrs ERJ and I engaged in years of negotiation.
Her concerns were the risk of a child or grandchild (or one of us once we are old) falling into a stand-alone, middle-of-the-room woodstove. If you watch the video at the top of this post you will see the inventor recording temperatures on the outside of his woodstove of 400F.
My proposal to surround the woodstove with a fence was objectionable from an aesthetics standpoint.
Our resolution was the fireplace insert and blower .AND. I have a woodstove in the garage that can be moved into the living space if/when things get REALLY bad.
Note to self: I need to get additional stovepipe, thimbles to pass through ceiling and other hardware. Just in case.
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