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[charlie]

Anyone running an Aspen 175?

[maine owb]

I am,

here is my post.

I own the Aspen 175 and live in Maine and began using it in mid january. I am working out a few problems but i do like the unit. During the 4 week period from mid january to mid february i used 1.5 cords of wood, this was a colder than normal month well below 0 many nights. I am heating a 3100 square foot house which includes a 600 square foot garage with 10' high ceilings. I am also heating my hot water. once the temp gets into the 30's the wood usage goes down. I estimate that i will use 6 cords of wood to heat my house and provide me hot water from November to May. I have kept track of every time i have loaded wood, what the weather was and how much wood i went through from week to week. During the coldest times of the winter i got a 12 hour burn time and once it's close to 40 degrees outside i get close to 24 hours. I used 1 1/4" pex buried 30 - 36" deep. Each line i insulated with 3/4" wall thickness foam and then wrapped with one layer of reflextix(looks like bubble wrap 1/4" thick). I then put each line in its own schedule 35, 4" pipe. For good measure i  put a 2' wide sheet of 2" rigid insulation on top of that. I have the boiler 75' from my house.

My wife is in the health field so it was very important to have a clean buring unit.

A few problems  i have had are that the  unit tends to drip a small amount of condensation in the front of the aspen during certain temps and i do from time to time get a bit of brown like condenstation on the foof of the boiler from the chimney. I believe this may be because the low stack temps along with dew point. You wouldnt see this in an older style wood boiler as much because the stack temps are higher. but that also means you will burn more wood and pollute more.

Freeze protection: My system has a 30% glycol solution giving me a low burst point. One good thing about the aspen is it only uses 75 gallons of water plus whats in the pex and it only costs a little over $200 to glycol the system. I believe this system has the lowest amount of water. It would cost a lot more to glycol most other systems.

My system also is isolated from my heating system using a heat exchanger. I believe this is important because the aspen like most or all outdoor wood boilers is an open loop system and hooking them directly to a closed loop system is not a good idea in my opinion. Because of this i have an aquastst that shuts the wood boiler circulator off if the water goes below 140 degrees. If the circualtor didn't shut off the oil burner it would heat the wood boiler water through the heat exchanger wasting oil. I also have a low temp aquastat on the wood boiler that turns the wood boiler circulator back on if the water drops below 35 degrees. This aquastat keeps the water between 35 and 45 degrees to further protect the system. I can now leave my house whenever for any lenghth of time without worry and without burning a bunch of oil to keep my house and wood boiler heated.

You also need a dump zone to keep the boiler from boiling over, my dump done has only come on a few times, less as i get better at understanding the wood loading part of things.

[willieG]

i must admit i do know NOTHING of your type of OWB but a dump zone?   I would try and see if i could heat my home with the aquastat set a little lower or add another 50 or so gallon tank to the system to absorb the extra heat before i dumped good heat to a "dump zone'

you are likely boiling yor stove now and again as you have only 75 gallons of water in your system...your stove is burning hard to heat your water and when it reaches (i am guessing) 180 and your damper (or blower quits) the fire takes a while do die down... and if the house is not calling for heat it is in this time that the water takes on exess heat and boils?

if you had more gallons in the system (a tank in the line in the basement)  or you heated your water to a lesser temp, this syndrome would not likley happen ...if that is indeed what is happening, as i stated i am only guessing at your setup

[maine owb]

ALL OWB will overheat. Most are an open loop system and if there is little demand for heat the system does not stop burning all together, Although It may not happen much I doubt most people have never experienced this. I am in the plumbing business and every system I know of has a dump zone. If not the water boils out the vent in the OWB. Most dump zones are a modine heater which removes heat from the OWB and puts it into the house or a garage. This is usaully set at 195 degrees. It is more important if you have glycol in your system. That stuff is too expensive to replace. Many OWB will only "warranty" their product if it has such a safe guard. The more water you  have, the more heat you have stored and if everything is satisfied that heat needs to go somewhere. Although nice, wood heat is not as exact a science as oil.

[willieG]

ALL OWB will overheat. Most are an open loop system and if there is little demand for heat the system does not stop burning all together, Although It may not happen much I doubt most people have never experienced this. I am in the plumbing business and every system I know of has a dump zone. If not the water boils out the vent in the OWB. Most dump zones are a modine heater which removes heat from the OWB and puts it into the house or a garage. This is usaully set at 195 degrees. It is more important if you have glycol in your system. That stuff is too expensive to replace. Many OWB will only "warranty" their product if it has such a safe guard. The more water you  have, the more heat you have stored and if everything is satisfied that heat needs to go somewhere. Although nice, wood heat is not as exact a science as oil.

i dont want to argue or cause trouble but the statement ALL OWB will overheat is not quite right to me. i agree with this statement ALL OWB CAN OVERHEAT (so can any hot water system,that is why pressured systems  have safety valves)

if your OWB is operating properly ,it will,  when the dampers close, smother the fire down to a smolder that will not produce enough heat to boil the water (if there is enough)  lets say you have 75 gallons of water in your stove..it heats to 180 and then the air supply is shut down (except for the amount  the factory has set to leak by too keep the fire alive) now the fire does not die down instantly and may continue to heat the water for several minutes..it is in this time that your stove may boil over because the 75 gallons is recieving enough btu to boil it...now if your system has 150 gallons in it when this "past the shut off" boiling takes place it has to heat an extra 75 gallons that 30 or 40 degrees before boiling and this gives the furnace enough time to smother the fire before this happens

i know for a fact that not all stoves do not have a dump zone...mine does not and i have never seen it boil under normal operations...now i agree it will boil out the top if a blower never shut off or an air feed stuck open  that is the "safety" of an OWB

many OWB have an overflow tank or the tank of the stove is big enough that it is not filled to the top to take care of expansion of the fluid but they are not a "dump zone" for unusable heat

this is the very first post i have ever seen about a dump zone on an OWB

i would be interested to know how many OWB brands actually have them?

[willieG]

[
i would be interested to know how many OWB brands actually have them?
[/quote]
i should have said  i would be interested to know how many manufacturers actually say you need them

[R W Ohio]

I have run our stove for three heating seasons,in weather from very cold to very mild and have never had a boil over problem.Our unit has a manual reset limit set to open at 190 deg.F and it has never tripped,so the aquastat set at 180deg.F off with a 20deg. diff. has not let the run over,even in mild weather go over the 10deg. difference between the 180deg.setting and the 190deg.limit setting.We do use a side arm for hot water and maybe this helps some.I have never seen more than a 3deg. overshoot at any time that I have watched it.

[maine owb]

My experience is with a gasification OWB which is a different animal compared to a non gasification OWB.

I should have said, "all wood boilers will over heat if operated incorrectly or a situation arises that allows it to overheat". I have a gasification wood stove and burn dry wood and my stack temperature is much lower than a conventional non gasification wood stove. That along with the fire brick creates an entirely different burn. It takes a temperature in excess of 500 degrees to re ignite the wood/gases in the fire box. The fire brick helps in this ignition after a long period of the blower being off. Even with the blower off the wood is slowly burning and if there is no demand for heat the water temperature can creep up(the heat needs to go somewhere). The  other common situation that i have seen is that a damper door gets stuck and the OWB over heats. I know people who do not have a dump zone and from time to time the OWB has boiled over (out the top vent hole). This also depends on the size of the OWB and the heating demand being put on it. I would say if you have never experienced your wood boiler over heating you are lucky and the system is working really good. I myself do not mind the occasional over heating because i simply dump the excess heat into my basement via a modine heater. I have glycol in my system and do not want any boil over situations. I have noticed that as i get better at understanding how to load the wood boiler i have had very little over heating situations.

3 reasons why i think a conventional OWB would not be as likely to over heat.....
1)Insulation/heat loss(some people)
2)burning green wood
3)higher stack temperature

 How well insulated the unit  and the supply and return lines are is important. My 1 1/4" pex lines are 3' deep and well insulated. I get almost no heat loss to the ground. I have seen some systems buried 2' or less where it is obvious during periods of snow where the pipe is buried (obvious heat loss). This single factor would  offset the small heat gain of a slow smoldering fire in the OWB. In addition to that if you burn green wood it is taking 40-50% of the available heat from that wood to burn off the moisture resulting in less heat going into the water (which would also help offset the slow rise in temperature of a slow smoldering fire). Thirdly, a conventional OWB has a much higher stack temp meaning less heat is going into the water. All of these combined would I believe result in the slow smoldering fire not increasing the water temperature during periods of no demand.
THOSE three things kinda act as a small constant dump zone.

A gasification boiler is a entirely different system that takes a different approach to running efficiently. Although I myself believe that a gasification OWB is the way to go I am not saying a conventional non gasification boiler is wrong. They have been used for many years and if people use them correctly they work.

[willieG]

My experience is with a gasification OWB which is a different animal compared to a non gasification OWB.

I should have said, "all wood boilers will over heat if operated incorrectly or a situation arises that allows it to overheat". I have a gasification wood stove and burn dry wood and my stack temperature is much lower than a conventional non gasification wood stove. That along with the fire brick creates an entirely different burn. It takes a temperature in excess of 500 degrees to re ignite the wood/gases in the fire box. The fire brick helps in this ignition after a long period of the blower being off. Even with the blower off the wood is slowly burning and if there is no demand for heat the water temperature can creep up(the heat needs to go somewhere). The  other common situation that i have seen is that a damper door gets stuck and the OWB over heats. I know people who do not have a dump zone and from time to time the OWB has boiled over (out the top vent hole). This also depends on the size of the OWB and the heating demand being put on it. I would say if you have never experienced your wood boiler over heating you are lucky and the system is working really good. I myself do not mind the occasional over heating because i simply dump the excess heat into my basement via a modine heater. I have glycol in my system and do not want any boil over situations. I have noticed that as i get better at understanding how to load the wood boiler i have had very little over heating situations.

3 reasons why i think a conventional OWB would not be as likely to over heat.....
1)Insulation/heat loss(some people)
2)burning green wood
3)higher stack temperature

 How well insulated the unit  and the supply and return lines are is important. My 1 1/4" pex lines are 3' deep and well insulated. I get almost no heat loss to the ground. I have seen some systems buried 2' or less where it is obvious during periods of snow where the pipe is buried (obvious heat loss). This single factor would  offset the small heat gain of a slow smoldering fire in the OWB. In addition to that if you burn green wood it is taking 40-50% of the available heat from that wood to burn off the moisture resulting in less heat going into the water (which would also help offset the slow rise in temperature of a slow smoldering fire). Thirdly, a conventional OWB has a much higher stack temp meaning less heat is going into the water. All of these combined would I believe result in the slow smoldering fire not increasing the water temperature during periods of no demand.
THOSE three things kinda act as a small constant dump zone.

A gasification boiler is a entirely different system that takes a different approach to running efficiently. Although I myself believe that a gasification OWB is the way to go I am not saying a conventional non gasification boiler is wrong. They have been used for many years and if people use them correctly they work.

 now i can not disagree with any of that..and i have never seen one of them new gasification stoves in operation and i do believe they are likley a much better stove (efficently) than any of the older ones . have heard good and bad things about them..the good things..they do burn less wood..the bad..they tend to need a lot more attention

however as i stated before..adding more water to a system will deter over heating ... one poung of water takes 1 btu to raise one degree...so to raise 75 gal from 180 to boiling takes 30,000 btus and that equals (even in an 100 percent efficient stove) very close to 4 pounds of dry wood but that same stove with 150 gallons of water would need 60,000 btus to raise the temp 40 degrees to boiling that would be about 8 pounds of wood if you doubled the water in your stove instead of boiling it may only go to 200

dont you agree that if your stove has only boiled a few times that doubling your water supply would act as a "dump zone" and not waste your heat but rather store it for use when an "appliance" calls for it? even if you continued to have your "dump zone" for an emergency such as a stuck air damper the extra water could recover the extra heat on most all "normal operational days" although as i have never ran one of these new stoves , having that much water would call for a longer burn timeto heat the water to 180,it may also be too long of a time between burns for the stove to "re-ignite"??

[maine owb]

Thanks for all the info..

One thing I did do was if there was an overheat situation i let it go to the hot water tank first which is 80 gallons, it is normally set at 120 so i let it max out at 150, then it dumps into the house via the modine heater. I think one reason why the aspen uses the 75 gallons unit is to help keep the unit warmer by allowing the firebrick to absorb a bunch of heat to help in re ignition. I'm guessing on that one, but they are more sensitive  than a non gasification unit. There have been times when my blower didn't come on for a long time, many hours and it didn't overheat. I also have never seen a problem with re ignition, even when the wood is all gone and there is a small pile of coals, I can load it up and the blower will ignite the wood. I think this is helped by the heat stored in the firebrick.

I value your opinion, it makes me think about all sorts of things that could be done. Being my first year with the unit i think i will get better at loading it and reducing any over heating situations. Looking back at some old posts it seems as this and re ignition problems have been talked about. I have read about someone dumping heat into a pool before.

In Maine you need a solid fuel license to install an OWB for someone and you need to be in the trades to get that. The problem is as with me, most heating guys know oil, not much guess work, but this OWB thing is so different that it really takes owning one and talking to other people who have them to get a good understanding as to best set them up. Not to mention unlike oil fired systems these OWB have only a few ranges in BTU output unlike an oil fired boiler you can match closely to a house. Then of course everyone is different. I want to beable to leave my house for days in the winter without fear of the thing freezing while my neighbor never leaves and keeps the fire burning every day of the winter.

Many variables. Good luck.

[willieG]

it will be good for the board to hear of the real experiences from people such as you with these "new generation" stoves so we may all hear the "owner operator' side of things such as actual wood usage and time and care teh stove needs to operate properly

i think i will be tackling a new stove for my "other place" and i want to only fire it one time per day...i have some old 36 inch pipe that has 6 inches of refractry in it (an old industrial smoke stack) and i am planning on trying to create a more efficiant stove with a 1200 gal tank (another freebee) that i hope i can get up to 180  or 190 degrees on one long burn and heat my 30 x 60 well insulated shop to 55 or so for a 24 hour period i still have to do the math to see if this is possable but it is stirring in the old noggin now and then