An appropriately designed hot water storage system with proper high efficiency wood boiler would cure a lot of your air quality issues, this system will not. It may be a nice monitoring product with some basic control functions that is of value but it doesn't cure the fundamental issue that a wood boiler only burns efficiently at full load.
You didn't mention the type of boiler you own but I am guessing its an Outdoor Wood Boiler that was installed in a building for convenience. If you look at the typically European indoor wood boilers they are specifically designed to operate with hot water storage to the point that most companies will not warranty an installation without storage. Unlike a pellet boiler that can control its output by introducing more or less pellets, the wood boiler is stuck with a full load of wood in the firebox, if the amount of heat you are using equals the boilers rated output everything is fine, the problem is when the amount of heat you are using is less than the rated capacity of the boiler, there is no way to take wood out of the firebox so the only way to reduce the heat output is to starve the boiler for air by closing the inlet air damper. When that happens, you go from relatively clean combustion to incomplete combustion which puts out a large assortment of very nasty chemicals that are going to potentially make you and anyone (or any other creature) in the area sick. Some folks and animals can tolerate it better than others but ultimately its an unhealthful situation. What makes it even worse is that climatic conditions that can cause a local temperature inversion where the smoke sticks around frequently lines up with part load operation.
If on the other hand, you put in a thermal storage system, the fundamental problem of part load operation is substantially eliminated except for start up cycles. How this works is you install a much smaller more efficient wood boiler usually equipped with a catalytic combustor which raises the efficiency of the boiler and reduces emissions. Once the boiler is up to temperature, the only substantial thing coming out of the stack is water vapor. In addition to the boiler, you have a large insulated steel tank which has to be sized for the size of your heating load and the size of your boiler. These two components work in tandem, the house is heated with hot water from the tank. It should be sized for a minimum of 12 hours storage for the coldest normal temperatures. When the tank temps start to get down too low, the wood boiler is started up and then run at full load for long enough to heat the tank back up to high temperature. During this time you will need to feed the boiler a couple of times as it most likely will have a small firebox but the big benefit is the boiler is running at full load and its not generating all the incomplete combustion gases and particles. Once you get used to it you will be able to time when to put in the last load so that the boiler runs out of wood before the temperature is up to storage. As the weather warms up you may only need to run the boiler once a day or maybe every other day. At some point it may not make sense to run it during warm weather but you can easily stretch out a tank for several days if its only hot water you need.
Its pretty easy to set up this type of arrangement to keep the propane boiler as a backup. What usually is done is the propane boiler senses the temperature in the hot water tank if the temperature is over a preset low temperature the propane boiler is prevented from running, if the temperature in the hot water tank is below that preset temperature, the propane boiler turns on until the tank is above the setting. I have the same setup for my oil boiler, when I head out in cold weather I run the wood boiler to heat up the tank and then go on my trip, at some point the tank goes below setpoint and my oil boiler takes over. There are a bunch of secondary controls that improve the operation of the system but any qualified installer will take care of these details.
Along with vastly improved air quality around your farm, you get big side benefit, the amount of wood you use is going to drop by typically 1/3rd. All those nasty pollutants in the air are mostly unburnt gases. With a good indoor wood boiler those gases get burned and turned into heat. I do need to warn you about a trade off that you already may be making. Wet wood burns cooler with a much higher potential for creosote and air pollution. An outdoor wood boiler is designed to burn wet wood but lots more of it and it can do it fairly cleanly at full output but the second the air damper closes due to lack of heat demand the volume of creosote and air pollutants increase substantially over dry wood. Modern indoor wood boilers aren't intended or designed to run on wet wood, they just wont run. Therefore you need to cut wood and dry it a minimum of one entire year and with many hardwood species like oak two years. This is pain initially for a new boiler owner as they need to cut and stack twice as much wood that first year or two but once over that hurdle the reduced work for supplying 2/3rd as much wood from then on makes up for it. By the way this also works to lesser extent for an outdoor wood boiler, properly seasoned wood is going to cut down on air pollution and wood used to lesser extent.
If you have read this and understand why hot water storage is so much better than an outdoor boiler you will probably ask why didn't you hear about this before is that a properly designed indoor wood boiler with storage is an integrated system that has to be designed and installed by someone who knows what they are doing and you typical propane dealer is most likely not qualified. These system are not inexpensive figure a minimum of 15K to 25K. The outdoor wood boiler folks offer the quick fix and the dealers work on hefty commissions. They are long gone before the owner realizes that they have voluntarily decided to gas themselves with all sorts of nasty pollutants for much of the year. If they are in area with neighbors, they also are subjecting them to the same issues. This is why many US states have effectively banned or restricted the use of outdoor wood boilers.
I have skipped over one other option which typically is for very large heat users like commercial farms, if you are over 20 cords a year you may want to look into a Garn, this is somewhere between an outdoor wood boiler and the indoor system I discussed. It is effectively an outdoor wood boiler with a very large water tank around the firebox. It is far more tolerate to wet wood but the large water tank means it rarely needs to run with the air damper shut. This option is even more expensive to install.
Hi Peakbagger! Thank you SO much for your detailed response. I really appreciate you taking the time to write this.
I will share it with my Plumber/HVAC guy and we will discuss things.
I will give you a little more information.
This is a learning curve for me, so please bear with me if I say things that don't make sense!
My plumber/HVAC guy has installed a number of indoor and outdoor wood boilers and is familiar with radiant heating etc. etc.
He is pretty knowledgeable and everyone around here uses him. I have visited lots of people he has done installs for, and looked at their systems, and I am confident he knows what he is doing. However, boilers continue to evolve, so there may be things we need to change.
The boiler I installed this Fall is a Benjamin (used) and it's actually an indoor wood boiler (although I would never put it inside my house). It is suggested that it be used in conjunction with another heat source, and from what I have discovered, because of some of the features it is lacking, they suggest it be used as back-up and not a primary heat source, so that could be part of the problem. We have made some modifications on it though, and overall, I don't think it is too bad....but it could be better.
However....having said that, the reason I wanted to try it before trying an actual Outdoor boiler was because of my concerns about the smoke inside my shop. I thought this one might be better since it is designed specifically for indoor use. After sinking money into a Woodpecker pellet boiler for a few years, I decided to change to wood because it was costing me way too much for pellets, and I couldn't get the computer to sync up with the thermocoupler in the water storage tank, so it meant that the boiler was running constantly- totally defeating the purpose of a 600 gallon insulated water storage tank!!
The Benjamin has a draft door on the front, and then we installed a damper on the back of it, as well as a draft regulator on the pipe. I play around with these in different combinations depending on the weather, but since this is my first year, I expected to be doing some tweaking. I think I am getting better at it- finding my groove- to keep it burning hot without smoke, but I'm just not sure about a couple of things.
I am burning well-seasoned hardwood, so at least that helps!
The pex tubing from the shop to the house is about 100' so there is some heat loss there, but generally it is pretty good.
One of the issues for me is the amount of time that I spend stoking it- especially on cold days. I had to stoke it every 3 hours (at least) to keep the heat up. We were lucky this year with milder than normal temps, but if it had been like previous years where we consistently had -20 to -30 C for weeks on end, I wouldn't have been a happy camper. I keep my wood/splits as large as I can but one problem with the boiler is that the door is SO small- I bet it's not more than 14" x 14"! I want something I can throw honkin' big hunks into!!
It was taking forever to get it up to 170, but it is getting faster as I play around with it. Once it is up there, it stays there for quite awhile. But, I am limiting the air for the simple reason that if I don't burn it slower, it is just wasting the heat and I end up stoking it for nothing.
I am still not making the best use of this 600 gallon storage tank either because of the small amount of wood the boiler holds, unless I am out in the shop continually stoking it, the circulator pump only gets to run for a short time, so the water never gets heated. Have to play with this some more (or get rid of it altogether.)
My next option is to remove the Benjamin and install an Outdoor Wood boiler (but put it inside my shop). There is a guy near us who builds these, and I have seen two of them in use (both installed inside buildings) and people are thrilled with them. They are very well designed, and can hold a LOT more wood than the Benjamin- and they cost the same as I paid for that one- about $2000. The one key thing that the Benjamin doesn't have is the fan to induce burning. The damper door on the front is automatically controlled and it opens and closes slightly, but that's it.
The one thing I thought about doing is putting a vented fan (like a range hood) above the boiler (but not so close as to draw smoke out). I might vent it to outside, or I might just try and charcoal filter one. Do other people use these? Any in particular that seem to work well?
When I saw the amount that people were burning a day in their boilers, compared to what I went through, it seemed like they were burning a lot less, (but maybe not???). What I DID like was that one guy put two big pieces in (maybe 18-20" x 18-20" ) and he said that that was enough to heat his old stone farmhouse (he just added some insulation in the roof a few weeks ago but stone is still pretty tough to heat) to 70F for a good 12 hours and when he came home it would still be burning.
I have a 2500sq foot 1857 log cabin, with 5 inches of foam insulation in the ceilings, but the windows need to be replaced, so I know I have some heat loss there. I close the loft, so I am only really heating about 1900sq feet. I have infloor heating in the stone floor of the kitchen, which helps heat everything of course. I keep that at about 70 and I usually keep the thermostat for the rest of the house at 65-67, which is really very comfortable in here, even on the coldest days.
I think my issues are due to the fact that this isn't really the appropriate boiler I should be using for this situation...but hey...everybody has to learn somehow!
My plumber and I were both looking at the boilers, so I bought the Benjamin and he bought one the guy built, but we might trade because he has a tiny house and we both think it would be ideal for that. I mean- it is able to heat mine no problem, but as I said, I am not into running out and baby-sitting it every two hours!!
If we trade and I put the bigger boiler in, I might just take out the 600 gallon water storage tank altogether.
I don't know....what are your thoughts about that?
I haven't bought one yet, but I am planning on getting an indirect water heater for my domestic hot water as well, and the plumbing is in place, but not hooked up, to heat my indoor hot tub too, (and eventually a pool in the summer).
I would LOVE to be able to afford to buy a brand new Garn or Froling, or maybe a Polar (do you have those? they are indoor/outdoor boilers but I think they might only be up here in Canada right now), but unfortunately, due to a number of things, I just don't have the money right now. Down the road though....!!
I 'think" you are referring to Gassification Boilers above? Yes I agree....that is my dream machine! (lol) but not in the budget for awhile.
Apparently this WoodMinder gives you a percentage of wood that is remaining in the boiler, so that alone might be handy to have, simply because I HATE winter and I hate trudging over to the shop to check the boiler only to find out it is still full (or empty!). With this boiler especially, it will be nice to have the propane boiler hooked up that will kick in if the wood boiler isn't generating enough heat (it is a nice model- Lochinvar) because even if I stoke it at 1:00 or 2:00 am in the winter, it doesn't last much past 7:00.
Anyways, thanks again for your input. I will share with my plumber and keep messin' around with things until I find something that works for me, but at this point, I think the bigger boiler is my first step.
Patti