When a boiler (which is designed to operate as a gasifier using a fan induced draft) is allowed to operate in idle mode (with the draft fan off), it really becomes nothing more than an OWB because gasification cannot occur without the fan (the fan is required in order to mix the smoke/gases from the upper primary chamber with the oxygen coming in from the secondary draft opening and colliding with each other to create 2,000 F temperatures in the lower, secondary chamber).
Thus, because a house cannot use all of the BTU's generated by this highly efficient, high temperature combustion and because most gasification boilers are designed with very small water jacket capacities in the boiler themseleves (which cannot possibly come close to absorbing all of the BTU's generated when gasifying), there are basically two possible ways to operate a gasifier effectively/efficiently:
1.) Continually (and often) fill the upper, primary chamber with small amounts of wood in an effort to closely match the BTU demand from the house. Obviously this would require more than a few trips to the boiler in a 24 hour period and most of us would not do this for very long before become very tired and frustrated. If too much wood is placed in the primary chamber (in an attempt to reduce the amount of daily trips made to the boiler for wood filling), the boiler will hit the high limit and go into idle mode. Too much of this idle-run, idle-run type of operation will cause large amounts of creosote to form and cause sticking problems with opening the primary door, opening the chimney/flue by pass lever etc, bridging of the fire wood etc.
2.) When used with adequate storage, start a fire and fill the primary chamber full of wood when the temperature in the storage tank gets to a minimum, pre-determined temperature (on my effect lambda 35 boiler with 1,000 gallons of storage I try to let the top of the top tank not get below 145 F when it is in the teens or below outside -by doing so I am able to keep my 3,000 sq. ft. house at a very comfortable 70-72F ). On real cold days this means that I would burn the effecta lambda for approx. 6-7 hours in the evening and by doing so am able to cover my homes need for heat for 24 hours.
If a gasifier is operated in a manner different than the two listed above one can expect decreased efficiency and nagging operation problems to arrise.
I have only had first hand experience with EKO and Paxo boilers but I am assuming that most gasification boilers (Biomass, Vigas, Tarm etc) are allowed to be operated in a manner which turns the draft fan off when a preset high temp. is reached and turns the draft fan back on when a preset low temp. is reached.
The effecta boiler, due to it being manufactured in Sweden and all the Swedish regulations which accompany it, will not operate in idle mode. It must always be used with storage and will shut off the draft fan motor and fully close both the primary and secondary draft openings when the water temperaure in the boiler reaches 96C (205F). In order to start the draft fan after it has shut down, the start button must be pushed. This took me a few days to get used to but having now operated my effecta lambda 35 for over 360 hours of operation, I really like this concept. In addition, it makes me feel good knowing that I am burning wood in the most efficient manner and with minimal emissions leaving the chimney. In a way, this than forces the designer/user/installer of the boiler system to give a lot of forethought to the type, size and location of the water storage system so that the end user is happy with the operation of the gasification boiler system once its up and running.
I realize it is difficult for many of us to change our wood burning habits especially after we have grown up with the "keeping a fire in the boiler 24/7" experience. It does take a little while to get used to but as with anything, once someone does the same thing over and over it becomes a "new habit". Knowing that this " new habit" is treating the environment well and is casusing less wood to be cut, split and consumed is a good reason to continue.
NWM