slls said:
I read you are more likely to get a hopper fire in a bottom loader, none of the Harmon owners complain of hopper fires.
hopper fires and smoke spillage generally only occur when one or more of the following apply,
1. hopper is not sealed: i once helped a lady over the phone stop a hopper fire in a harman , when the glass top in her hopper broke, used sheets of tin foil across the hopper opening to seal it long enough to get the unit shut down normally worked well in that instance (she wasnt having an actual blown out fire but it was smoking "a crap load" in her words, to credit the dealer , they came out the next morning and corrected the issue with a new glass piece, she had dropped the hopper lid down after filling accidentally and the glass broke. all was well after the incident and we still chat on occasion in a different forum, was worst case scenario, had just lit the stove , then decided to top the hopper , the pipes hadnt heated up yet so no convective draw, new owner first year with the stove.
2. excessively dirty stove: ash will build in a stove that burns wood , and pellets are wood so they make ash. ash carries through the burn chamber into the "heat exchangers" to the flue the more that accumulates the more it restricts the flow of air. during a shutdown without letting the stove clear , such as a power failure or component failure the natural convective flow removes the smoke as the fire smothers out. if the unit is loaded with ash , that flow is restricted, keep in mind that during this time there is a bunch of heat building along with the smoke in the burn chamber. this creates pressure, the pressure is releaved by the easiest path availible , if the flue is clogged then it will expand radially until releaved. if there is not a hermetic or close to hermetic seal in the hoper , then that heat is pushed there by this pressure, htis causes the pellets there to cook and in some extreme cases to ember up , though ive never seen an actual flame i have seen embers (bear in mind that i do this for testing purposes so i create this scenario to learn from it) what i learned is , keep your stove and flue clean and this wont happen in literally any circumstance , the lady i mentioned above was caught in the worst possible case, and the unit had run for quite a while with her just dumping the ash pan and not paying atention to the rest of the stove.
3. bad install: having a vent with no vertical can easily help bring this about as well. ive seen vertical DROPS! in vents , folks think , well the blower pushes it out so it is ok, NO it isnt! in a power outage this will ALWAYS cause a smoke incident. avoid long horizontal runs an multiple elbows which restrict flow , heat wants to go straight up, not sideways and around corners.
4. negative pressure: when a pellet stove is running if it is pulling air from inside the structure it is likely reducing the ambient air pressure inside the structure in relation to the outdoor pressure. this is a "vacuum" effect which when the mechanical pull of the air from the blower is removed , the vacuum pulls against the flow stronger than the convective draft of the vent can fight , smoke is then pulled right out through the intake opening for combustion air (the hopper may not catch fire but the smoke can get pretty thick in a bad case).
all this boils down to the same thing, manufacturers test their designes exhaustively (we spend a boatload of money constantly as im sure every other manufacturer does) , to reduce the possibility of this happening. but it does on occasion , virtually always due to one or more of the above criteria. to avoid this situation , read and follow VERY CAREFULLY the installations and operating instructions for whatever unit you buy and install. the odds of having an incident like this are astronomical if all is as it should be, the odds can become almost "betting odds" if the unit or its installation are ignored, neglected , or improperly done.
please keep in mind , i do not write this to scare anyone , i have worked in this field for 15 years, any stove can burn back into its hopper or release smoke into a dwelling if the right conditions exist. if they dont , they are as safe a heating appliance as you will find regardless of the fuel it burns. simple solution. do the install right , and do what the manufacturer asks in regards to maintaining your unit. and enjoy your stove.