First week burning wood

I have a good week under my belt burning wood and it is definitely a learning curve (and I still have a ways to go as it’ll change as the weather gets colder). First, I am glad I got the manometer so I can see what my draft is. A manometer uses pressure and/or suction to tell you what the pressure difference is visually using a liquid in a tube to show you the measurement. I am using this Dwyer manometer¬†along with an insertion tip (this one, but I’ll be honest that I am not sure if it is the right one or not as it was a BEAR to get the tubing on the tip, I think it is meant for the next size up but I made it work). I can easily see if I am getting my minimum .04″ of draft or exceeding the .08″ max draft; I leave it hooked up all the time right now. Without running a barometric damper I was easily hitting .08″ when the furnace first fired up and .11-.12″ with the damper open and fire raging. Running at that level for extended times is either not safe or will make my furnace not last long. The draft will only increase as the temperatures go down, so a barometric damper is a necessity. I have more thoughts on the barometric damper I’ll put in my next post.

My first fires I built a bit too close together in time and the house got up to 78 degrees. Whoops, don’t want to do that again. The next I didn’t use enough wood so while I got the house temp up to a comfortable level it didn’t sustain very well. With the wood furnace you can’t really hold an exact temp, so you’ll run it up to 73 or so and then it’ll sustain there for maybe 2-4 hours (depending on the size of the load) and then start slowly dropping a degree every 45 minutes to an hour afterwards as the coals will still let the fan kick on, but not hot enough or frequently enough to sustain the heat. Now, so far this is based on 45-50 degrees during the day and 35-50 degrees at night observations.

Right now I am decent at estimating the size of load I need to not exceed 75 in the morning and let it still be about 70 when I get home from work 10 hours later. There frequently aren’t any coals left; I am not sure that I can really expect there to be coals left after that long. This will be particularly true as it gets colder and my wife may turn the timer on to warm it up; thus burning off the coals more. But, if I have a completely stuffed fire box I’ll have the best chance at the coals lasting; but its hard to get a full load fired completely (which you must do with the furnace) unless it goes for a long time or there is a nice bed of coals already present; thats typically not the case when I wake up in the morning right now.

So I mentioned a timer. My wood add-on furnace (which I didn’t add-on, but ran completely new ducting) has an on/off switch that makes the damper either be open or closed, or there are terminals to hook up a thermostat. I put a 60 minute spa timer on my furnace (secured with a self drilling screw and hooked to the terminals) so I can crank a specific time on there for the damper to be open and then it closes again if you have the switch in the off position. When you first fire the load you have to run it hot enough long enough to completely char all the wood per the manual. This requires the damper to be open 20-40 minutes depending on how packed the firebox is and how many coals there are to jump start the fire. Well, it is very easy to forget that switch in the on position and either make the house unbearably hot, or make the furnace be WAY overfired. This is especially true if you do not have a barometric damper or a faulty one (which I did have, again, I’ll delve into that in my next post). I think it is pretty unsafe, so I have put several layers of aluminum tape over the switch so it can’t be used. As far as a thermostat goes, you’d want to be pretty careful what thermostat you use. When there is a bed of coals or charred wood, if you open the damper for 5-10 minutes and thats all, it is not going to get a good burn going again in such a short time. This means more smoke, less efficiency, and more wood use. What I think you’ll want is a thermostat that will let you adjust what the temperature swing is (really what you want is to open the damper for a minimum amount of time, you could do this with external electronics but the temperature swing is probably good enough). This probably means a digital, likely a programmable thermostat. I don’t believe honeywell units let you adjust this setting. I did some research and found this LuxPRO thermostat¬†will let you adjust that setting and it is in the $35 range so pretty affordable. I think if you set it with a +/- 2 degree F swing that would be okay. If you set it at 72 it would kick on at 70 and turn back off at 74. When the damper closes there will likely be enough heat to carry it another degree. So I’d probably set it at 71 and kick on at 69 (still warm enough) and off at 73 which may go as hot as 74 or 75 (not TOO hot to be unbearable).

I’m not sure if I’ll end up hooking a thermostat up or not or if I’ll just have my wife turn the timer for a set time to bring the house back up a few degrees. I marked the timer with a sharpie at the 30 minute mark so there is an easy visual to see that it is turned to the right spot. 30 minutes with new wood will raise the house 3-4 degrees, but on coals it takes probably 10-15 minutes just to get them firing again, so it is only good for 1 or 2 degrees. That is true right now, when the damper is closed the furnace barely reaches the .04″ minimum draft, so the coals do not burn extremely hot. As the weather gets colder the draft should increase and so the coals should be hotter and ready to burn hotly more readily. So the temperature increase may larger as the temperature drops (or the temperature may counteract that).

So at this point after a bit over a week the propane furnace has not kicked on a single time! That will be a GREAT savings in propane. My house (about 1400 square feet finished upstairs I’m heating with duct work, 1400 sq ft unfinished walkout basement) here in Michigan is insulated decently in the attic, though walls are only 2×4 construction and so pretty limited insulation in the walls. That said, when we kept it at 68 in past years we’d go through about 1000 gallons of propane per year. I figure about 700 gallons of that is used during the Nov/Dec/Jan/Feb time that I’ll be able to heat with wood. A bit more is used in the Oct / March months where it may be warm enough that I may not use the wood since its a bit awkward if it 50 or warmer. About 200 gallons or so is used for hot water, cooking, and laundry and will be a constant even with the wood heat. So 700 gallons at $1.50 a gallon is $1050 in propane savings. My home insurance is going up $150 a year for the wood burner, so $900 in actual savings since I have free wood from my property (I should use 3-4 cords per year). I am looking forward to that, and its great timing since I just noticed a lot of rustyness from my hot water. I think I’m due for a new water heater as this one is original to the house circa 2000. I’ll upgrade to a high efficiency tankless (the $300 or so difference in price will be paid back in about 4-5 years due to the efficiency difference between that and a normal direct vent water heater). Still, at least its offset with not having to buy propane! The whole stove / chimney / duct install will break even after next year.

One side benefit, the wood furnace operates with only 210 watts, and that is only when the blower is running. That is low enough I can run the thing off my boat’s deep cycle batteries (2) and an inverter for about 11 hours of blower time (that should be two full loads or about 16-18 hours total) and have power during a power outage without even having to fire up my generator!

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