Wood feeding freqency

[sfriedri]

I live in Southwester Ontario in a reasonably well insulated 2500 ft2 home. I've been heating with wood for quite a while using a Pacific Energy wood stove, and am considering installing a wood gasification boiler in my garage. I'm hoping the boiler will have several advantages over my wood stove, one being the frequency that I need to feed the fire. I know that feed frequency will depend on different factors, including my plan to install 800-1000 gal of storage. For those here that have an EKO or Tarm boiler with storage, I'd appreciate any information on how often you find you need to feed the unit. My preference during the main heating season would be to rarely need to restart the fire. In the ideal case, I could simply scrape around the remaining coals and then re-feed the boiler without needing to use any kindling to help the fire get going. This is my current practice with my wood stove, and I can keep the stove going for weeks without needing to restart the fire or use any kindling. With a Tarm or EKO coupled with heat storage which would cause a relatively high burn rate, would I realistically be able to feed the fire say 3 times/24 hours (morning/noon/evening) and not need to do anything other than scrape around the coals and throw more wood on? After a 12 hour period, would there be enough coals left to restart the fire?

I also have a basic question about heat storage using open versus closed loop. Is the main reason for using a tank with a heat exchanger versus simply circulating the water in the tank to reduce the potential for corrosion in the boiler? I assume closed loop systems are used because it is easier to control the quality of the water in a smaller, closed loop system.

Thanks for your help.

Stuart

 

[Eric Johnson]

Welcome to the Boiler Room, SWF.

I pretty much ran my boiler last winter as you describe with no storage. Not that much different than my old conventional wood-fired boiler, in that I tried to build fires that would reflect the weather and always leave me with a small bed of coals in the firebox. That's a good way to keep smoke to a minimum, since a refractory mass with hot coals sitting on top of it won't usually smoke when you stoke it up, as opposed to starting a fire from scratch, with can be a little trickier, smoke-wise. At least with the EKO.

I'm not sure how storage would affect that situation, though the preferred method seems to be to fire up the boiler once a day or once every other day. But I think you could probably figure out how to take full advantage of your storage and generally have a bed of hot coals to work with.

So I guess the short answer to your first question is yes.

When we talk about closed loop vs. open, what we're really talking about is pressurized vs. nonpressurized. A non-pressurized tank is a lot easier/cheaper to build/buy than a pressurized one. You can use a 500 or 1,000-gallon propane tank for pressurized storage, but you will also need a big expansion tank for all that extra water volume. A nonpressurized tank needs an expensive heat exchanger, but the hx gives you a bit more flexibility. There are many tradeoffs to both approaches; probably everybody doing it one way at one time or another wishes he'd gone the other direction.

 

[sled_mack]

SWF,

I have a similar sized house, but not well insulated, and a bigger storage tank. I have my EKO on a timing relay. It burns for 4 hours, then shuts the fans down. (I have an aquastat to run the pumps even if the timer has expired to protect the boiler.) During the main season I load the boiler twice a day, then reset the timer for another 4 hour burn. 4 hours is enough to recharge the tank and leave plenty of hot coals and chunks of wood to easily start the next fire.

It may not be the most efficient use of the wood compare to theoretical, but it saves a lot of labor of starting fires.

 

[deerefanatic]

Welcome to the Boiler Room, SWF.

I pretty much ran my boiler last winter as you describe with no storage. Not that much different than my old conventional wood-fired boiler, in that I tried to build fires that would reflect the weather and always leave me with a small bed of coals in the firebox. That's a good way to keep smoke to a minimum, since a refractory mass with hot coals sitting on top of it won't usually smoke when you stoke it up, as opposed to starting a fire from scratch, with can be a little trickier, smoke-wise. At least with the EKO.

I'm not sure how storage would affect that situation, though the preferred method seems to be to fire up the boiler once a day or once every other day. But I think you could probably figure out how to take full advantage of your storage and generally have a bed of hot coals to work with.

So I guess the short answer to your first question is yes.

When we talk about closed loop vs. open, what we're really talking about is pressurized vs. nonpressurized. A non-pressurized tank is a lot easier/cheaper to build/buy than a pressurized one. You can use a 500 or 1,000-gallon propane tank for pressurized storage, but you will also need a big expansion tank for all that extra water volume. A nonpressurized tank needs an expensive heat exchanger, but the hx gives you a bit more flexibility. There are many tradeoffs to both approaches; probably everybody doing it one way at one time or another wishes he'd gone the other direction.

Ok, not to hijack, but........ I'm planning on using my 1250 galllon bulk tank as open (non-pressurized) with an open-top expansion tank with wax on it...... Not really open, not really closed........ I don't plan on using a HX... Just plumbing it like a closed system. Is this asking for probs? Everything in this system with the exception of my circ pumps will be either copper, brass, or pex......

 

[jebatty]

Early on I concluded that starting from coals all or most of the time would be the best, but with 1000 gal pressurized storage, I now generally go with a 2 load burn, which bring the tank up to about 170, and then not burn again for 1-2 days and even longer in really mild weather. In our coldest winter (-30F), I will do one load burn per day to maintain the tank temperature.

Firing the Tarm from a cold start is very easy, usually within 10 minutes it can be started, loaded, and walk away. I no longer give thought to insuring coals are available for a restart, although if they are present, I will use them.

The pressurized storage is closed loop, and I'm finding the most direct advantages are 1) not needing to add water or monitor water volume, 2) not needing to monitor pH and be concerned about corrosion issues, and 3) once the water is conditioned (pH, O2 scavenger, and buffer chemicals), the system is and remains "clean" and rust free with a steel storage tank and black steel pipes.

I started with an open system and the Tarm isolated by a plate hx from the storage. I'm still staying with the isolation, even with pressurized storage, for now, mainly because that's what I started with.

 

[Eric Johnson]

I would agree that starting a fire from a cold start is not hard at all.