Replies

1. 
   eawood | Oct 13, 2014 11:12am | #1

   Alex,
   an add on catalyst will likely do little to eliminate the smoke issue. If the gasses are dark enough and of significant quantity to annoy a neighbor most likely they are too cool to heat up and fire a cat. I would look elsewhere for a solution. What model stove/boiler are you using and what type and how dry is the wood you are feeding it? What is the general setup of the system, how many square feet are you heating and is there thermal storage?

2. Expert Member
   Dana Dorsett | Oct 13, 2014 11:40am | #2

   I'm assuming what you have is in fact an outdoor wood BOILER, not a stove(?). The problem with most outdoor wood boilers is in the controls, which throttle the dampers down to a smolder mode when the storage aquastats are satisfied.

   When the thing is running full-bore it's emissions levels are modest, but when throttled way down they soar, and having an additional catalyst won't appreciably change that condition.

   With an 8" bore that stove/boiler probably ridiculously oversized for the thermal loads it has to serve. In those cases one solution to the down-throttling issue is to use smaller fuel batches and only burn at high temp, allowing it to burn until nearly extinguished without hitting the high-limits on thermal tank aquastats or thermostats. This is less convenient for the operator, but it does mitigate the emissions by a large fraction.

3. 
   alexzan | Oct 13, 2014 11:59am | #3

   Thanks so much Eric!

   Here's some more info:

   We have one of these blue stoves installed in a shed about 50 feet from the water heater (I'm not sure of the exact model number, since we bought it many years ago and right now I don't have access to the paperwork):

   http://www.econoburn.com/

   The wood is mostly hardwoods, maple and oak, which has been drying, covered over the summer months. It's pretty dry but from what I gather oak can take longer to dry out. Our shed is waterproof.

   We're heating about 2500 square feet, with radiant heat on the ground floor, and radiators upstairs. We don't have thermal storage, but since the home has a concrete base it does hold the heat well.

   Additional question: for the first time this year we tried running the stove at 140 degrees in the late spring/early summer, rather than oil, which has become really pricey. This was when the neighbors mentioned the problem, so we switched to using oil.

   Do you think it was the lower temperature that exacerbated the issue? Maybe now that it's down to freezing at night, if we bring it up to 160 might it burn hotter and emit less?

   Again, your expertise is much appreciated!

   Alex

4. 
   alexzan | Oct 13, 2014 12:11pm | #4

   Wow, thanks Dana!

   That's extremely helpful too. I'll run this info by the family and the neighbors, and we will proceed to put it into action once the temp goes down a bit more. It'll mean more trips to the stove but less pollution.

   Also I didn't know the distinction between a wood stove and a boiler, thanks for pointing that out. (Heck, I'm a musician, so I'm way outside my field of knowledge here, hahah).

   Many thanks,

   Alex

5. Expert Member
   Dana Dorsett | Oct 13, 2014 01:57pm | #5

   A code-min 2500' house in New England will have a design heat load of about 30-40,000 BTU/hr. The smallest Econoburn outdoor boiler (EBW-150-O) has a rated output of 150,000 BTU/hr. It's way oversized for the load. While it has 37 gallons of water as internal thermal mass, it's not nearly enough mass (even with the concrete thermal mass of your radiant floor) to buffer a lot of heat. Adding 500-1000 gallons of thermal buffer would likely eliminate the need to run 5-10 small burns/day instead of 1-2 big ones, and it's a common solution. But since EBW series are pressurized boilers, large tanks with the necessary pressure & safety ratings would be pretty expensive. (Compared to a few season's worth of heating oil it might still be worth it though.)

   In the mean time you raise the temp to 160F or higher (whatever it takes as a max) it will take bigger loads of wood without tripping the dampering-down control, which would ease both the inconvenience-factor and lower the emissions by having longer higher-temp burns. When firing intermittently and allowing it to burn nearly out rather than dampering down the majority of the emissions will be in the first ~10-15 minutes as it's coming up to temperature. Once it's at temp you should see almost no visible smoke coming out the stack.

   Another "solution" would be to install a 75-80' stack to have more guaranteed dilution, but I'd be pretty surprised if the neighbors thought that really worked for them... ;-)

   In Massachusetts if a neighbor's house is within some distance of your wood boiler they have the legal right to shut it down, even if you were there first. I think the state-wide restriction is a minimum of 250' from the property line, and 300' from any house or outbuilding on the abutting property, but many town building codes have increased that to 500', 600', even 800' or more.

   With an oil-burner the "safe" MINIMUM temperature of the boiler would be 140F. Below that temperature you will begin to to have acidic flue condensation issues that will degrade the flue (unless it's stainless steel), and if the boiler is much below 135F that destructive condensation can occur on the heat exchanger plates. While there is some amount of efficiency to be gained by running it a lower temp, the bigger efficiency gains would be had by increasing the differential between the minimum and maximum temperatures, which keeps the burns long rather than short-cycling it in an narrow range between 140-145F or something. Increasing the temp increases the jacket losses of the boiler, but that's not as bad a hit as the ignition sequence losses of having 10x as many burner cycles.

6. 
   alexzan | Oct 13, 2014 02:12pm | #6

   Wow, you're amazing.

   Really REALLY appreciate all this info. You folks sure know your stuff.

   Also interesting about the property line, we'll have to measure that...

   1000 thanks from us, and we'll be putting your advice into practice sooner rather than later,

   Alex

7. Expert Member
   Dana Dorsett | Oct 13, 2014 04:08pm | #7

   Naw, I don't know anything- I just make it up as I go along (you can even ask my wife! ) I just get lucky on this stuff a lot of the time... :-)

   If it happens that you are located in MA, it's worth looking up the local code setbacks for outdoor wood boilers are in your town. This is an issue that has come up in many states, even resulting in lawsuits when neighbors couldn't figure out how to be more neighborly about it. Run a web search on these terms and you end up with a bunch of them, but if you insert the name of your town you'll probably find the more relevant numbers:

   outdoor wood boiler distance massachusetts