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[muffin]

I am wieghing two systems right now.  One from Aquatherm with a closed system and 76gallons and one from Earthoutdoor with an open system and 350 gallons.  I have an indoor pool which will put a very long duty cycle load on the system as I expect it to run 6-8hrs a day with a load of around 100K BTUs.  Both units are around 350K BTUs.  I also have 3 zones in my house that will be heated with this as well as my hot water.  I am concerned that the small gallon unit will not be able to handle the peak loads well and will have issues.  Any thoughts?  All combined I probably have 500K BTU if everything turns on at once.  I would expect the heating systems should have short on times so hopfully that doesn't happen often and the overlap is short duration.

[rhugg]

It is about energy capacity and 300 gallons gives a lot of buffer for smoothing.  76 gallons is at the low end of any boiler.  I have a big reservoir and the only negative I see with the bigger reservoir is that the unit doesn't cycle as often.  If the unit can only burn at 350k BTU's there will be times when you are trying to pull 500k btu's.  Temperature will drop faster in the 76 gallon unit until either some of your demand shuts off or because of the lower water temperatures the loads balance the capacity at 350k BTU (Amount of heat transfer decreases with the temperature differential).  If the smaller unit had more burning capacity I might consider it equal but I think you have a valid concern.  Maybe you put your pool on a timer so it runs during the day when there is less heat demand.  I have my pool circulator in line with my pool pump which is on a timer.  The pool is a hog especially when it is not up to temperature. 

[muffin]

Anyone else have thoughts on this?  I really need to make a decision and I like the thought of a closed system but am really afraid the low gallonage is going to cause problems.

[Ridgekid]

I agree with rhugg.

[willieG]

i agree storage with wood heat is a must. remember a gas or oil burner with 76 gallons can deliver the btu output of its rating  continuosly as the fuel supply is constant. your wood boiler fuel supply grdually gets smaller the whole time untill you get out there and add more wood. so as your fire burns the btu output acually decreases by the minute at a cetain point. here is a little story that might not even be relevant but i think it is and has probably happened to anyone who has had a OWB for a few years....i have on occasion came home late from an "evening out" and loaded the furnace and before loading shut the blower off as it was running when i got there. after loading the furnace i forgot to turn the blower back on. in the morning the house is still warm (about 70) but when i turn on the tap to get water for coffee the hot water is only like warm...oh oh...out to the stove and discover the fan is off. the 160 gallons on my stove was able to heat the house all night without burning any wood..i can assure you with only 76 gallons the house would have been quite chilly the stove had lost about 60 degrees in about 8 hours on a cold winter night. if i were to build another stove (and i am about too) it will have a min. of 300 gallon tank and it will be an open system. good luck on your decision

[muffin]

i agree storage with wood heat is a must. remember a gas or oil burner with 76 gallons can deliver the btu output of its rating  continuosly as the fuel supply is constant. your wood boiler fuel supply grdually gets smaller the whole time untill you get out there and add more wood. so as your fire burns the btu output acually decreases by the minute at a cetain point. here is a little story that might not even be relevant but i think it is and has probably happened to anyone who has had a OWB for a few years....i have on occasion came home late from an "evening out" and loaded the furnace and before loading shut the blower off as it was running when i got there. after loading the furnace i forgot to turn the blower back on. in the morning the house is still warm (about 70) but when i turn on the tap to get water for coffee the hot water is only like warm...oh oh...out to the stove and discover the fan is off. the 160 gallons on my stove was able to heat the house all night without burning any wood..i can assure you with only 76 gallons the house would have been quite chilly the stove had lost about 60 degrees in about 8 hours on a cold winter night. if i were to build another stove (and i am about too) it will have a min. of 300 gallon tank and it will be an open system. good luck on your decision

Thank you so much for this input.  You mention your next one would be an open system, why?  I was acutally thinking the closed system would be nice.

[willieG]

open system= no pressure..no pressure no suprise scalding or worse if soemthing were to go wrong no pressure inspection needed to appease any government or insurance agents. you can hook an open system to a closed system (if you all ready have one) and keep the two systems completely seperate from each other. (thier waters never mix) my open system now in use just finished it's 11 th winter and fo the last 9 i have not used any water treatments and i have never had a problem with the stove. I sometimes think this water treatment thing is a way for buildiers to get out of warranty issues or just to keep you buying the stuff. I would say it likely does help to some degree but i stopped using it as my stove is home made and is nearly 1/2 inch thick. I think it will last a long while yet. I am not trying to talk you out of a closed system it is just that i think open systems are a lot less worrysome. and this is just my opinion there are likely many more that would opt for the closed system. that is what makes this board so good, opinions and opposing opinions can be made without personal attacks on one another. you will have to sipher through all the different ones you get and make your decision...good luck