Archive for January, 2011

Wood Stove Insert

Tuesday, January 4th, 2011

I bought a wood stove and was optimistic that it would heat up the house, but was surprised on how well it did.  I bought a Jøtul C 550 Rockland model, with one of the drivers being the energy tax credit, and all the wood I have access to.  The brand generally had good reviews and it was more contemporary than most and would match the rest of the room.

Jotul 550 Stove

I was able to heat the house without running the gas furnace, on some very cold days.  Takes a while to get the room/house warm, but once it gets warm it stays and the heat rises to the 2nd floor, so the 2nd zone isn’t used when the stove is running.   The walls are cinder block and the main living space is very open, so air flows very well.

I was curious on how to optimize and instrument the stove.  Also, had a few too many days off around the holidays.  Started with measuring temperature of the room, the furnace duct (to know when it was on), and under the stove.  The white cord on the left is a temperature sensor (HA7 1 wire controller), and used to generate a chart below, of the air temperature under the stove.  The temperature at the top of the stove is about 575 F, at 8pm, and the room temperature was rising about a degree, every 6 minutes.  The stove temperature exceeded the 1-wire specs, so I bought an infared thermometer for about $40 from Harbor Freight, and put the ha7 sensor on the intake side.

The one thing that doesn’t work well is the blower auto control.  Seems to be a consistent gripe from other customers.  The blower on this model has a manual, off, and auto setting.  The auto setting is supposed to turn the blower on when the stove is hot, and off when it cools.   There’s a switch on a heat sheild on the bottom of the stove and I can measure the stove temperature to over 500, and the switch temperature to over 120F, and the blower doesn’t always turn on.  Seems like more ash, insulates the bottom, and affects the switch, and even without ash, it’s not reliable.  Ordered a few similar switches and some thermal silicone to see if I can get it to work more reliably.  For now I use the manual setting.  As an aside, I measured the blower to burn about 70 Watts using a TED 5000.

The other  variables are around the wood.  Specifically, the type of wood and moisture content. Lots of content on the web, and the basic concept is that dry firewood has a 15-20% moisture content.   In ideal conditions, as the fire heats up, the resin mixes with air and becomes combustable, generating more heat.  If there’s higher water content in the wood, the water gets mixed in with the resin and instead of adding to heat, it prevents the combustion, which is bad for allot of reasons (less heat, creosote, soot, etc..).  Tried to find a reliable DIY way to measure moisture, and many expensive tools are just glorified ohm meters.  One approach is to cut a 1 in piece of wood, measure the weight, then dry it in an oven at 215-217F.  after the weight stops dropping (~12 hours), measure the change in weight. That delta is the removed water.  Percent moisture content in the original sample content would be:

(original weight – dry weight) /  dry weight

Kitchen oven doesn’t get much use, but using this approach is interesting, but too much work.  Decided getting a moisture meter from home depot.  Ordered it online, and will see how consistent it is with some of the wood piles.

Next time I get some time off, I’ll collect some more data…..