owb tip

[bnew]

Ive been heating with an owb for 5 years now, in two different houses. I save a lot of wood by running mine much cooler than recomended.Try lowering your water temp and let the furnace blower run a little longer.In a crappy insulated farm house(2465sf)I was burning about 7 cords insulated pipe above ground.

 

[Butch(OH)]

My Woodmaster came set 160 on 170 off. I found that that side arm water heater heats a lot more water when the OWB is set at 180 than 170 so I set it up to 180 on the weekends when the wife is running the washing machine around the clock. I also have found that it seems to burn quite a bit more wood (given what is being asked of it), at 180 than at 170 so what you say makes sense to me. I also found that the inside of the OWB stays much cleaner when set at 180 than 170 but thats really not much of a factor. What temps are you running?

 

[Husky137]

I don't know how true it is but I've read that low boiler temperatures can result in corrosive condensation forming inside the firebox and can lead to shorter firebox life.

Agreed on the corrosion point.


I don't see how a lower temperature is going to be anymore efficient than higher temperatures given your heat losses are going to be the same regardless. After all the OWB is merely making up the heat loss from transfer to the house and the heating of the house. It's not like starting at zero everytime. Maybe I'm missing something in a simple algebraic equation.

 

[rx7145]

I also run my Boiler at 165* on and 175* off. Does seem to use less wood. Also the pumps seem to like the cooler temps as well.

 

[bnew]

Right now Im keeping my water 140 to 150. Tonight it going to be 16 degrees, so Ill bump it up 10 degrees. I have an older Taylor unit with a draft fan. It saves wood by not calling for more heat as often. I have a 36" fire box and getting 20 to 24 hour burn times.

 

[Husky137]

Right now Im keeping my water 140 to 150. Tonight it going to be 16 degrees, so Ill bump it up 10 degrees. I have an older Taylor unit with a draft fan. It saves wood by not calling for more heat as often. I have a 36" fire box and getting 20 to 24 hour burn times.

Your house isn't using the heat as fast then.

Here is my line of thinking.

You run an OWB at 170-180, it drops to 170 and starts the fire, it takes x amount of wood BTU's to move the temp back up 10 degrees to 180. 140 -150 you are still heating the same 10 degrees. I don't see a variable there that would save you any wood.

Now there are all kinds of other variable such as species of wood, green or seasoned, heat load being called for from the house, etc. that could effect wood consumption and burn times.

 

[joecool85]

Right now Im keeping my water 140 to 150. Tonight it going to be 16 degrees, so Ill bump it up 10 degrees. I have an older Taylor unit with a draft fan. It saves wood by not calling for more heat as often. I have a 36" fire box and getting 20 to 24 hour burn times.

Wow, and it still keeps your house nice and toasty?

 

[fourapples]

I have a stainless model with factory setting of 160 and drop of 5 degrees to start up the blower. It heats 1800 sq ft farmhouse and with plate type water exchanger we get all the hot water we need. Burn time is 24 hours per load. Forced air heat exchanger seems to keep up OK but temps have not been below 20 so I am sure I will use more wood when it really gets cold. I was told to increase drop off from 5 degrees to 10 when it gets really cold to lengthen cycle time intervals.
I would think that the hotter the water setting the more wood that would be used regardless of identical drop off ranges. It requires more heat and more wood to maintain a 180 degree temp than it would a 160 degree temp. Just my thoughts.

 

[cunrya]

I don't claim to know any of the science behind all this but, I played around with it for awhile last year and seemed to get the best wood mileage at the 165 to 175 setting on mine (Central Boiler) Much lower and it seemed to take longer and use more wood to heat the domestic water. Set hotter the burn times seemed to a little shorter. As was said before though there are so many variable involved it more of a seat of the pants guess than anything I think.

 

[joecool85]

I don't claim to know any of the science behind all this but, I played around with it for awhile last year and seemed to get the best wood mileage at the 165 to 175 setting on mine (Central Boiler) Much lower and it seemed to take longer and use more wood to heat the domestic water. Set hotter the burn times seemed to a little shorter. As was said before though there are so many variable involved it more of a seat of the pants guess than anything I think.

I think bnew is only using his for heating his house, not domestic hot water, this may be why he can get away with running 140-150 degrees.

 

[Husky137]

Theoretically a boiler at a lower operating temperature should have lower energy losses to the outside air. If a boiler is at 175f and it is sitting outside in 20F air the temperature differential is 155F(175-20). A boiler at 145F at the same outside air temperature of 20F would have a temperature differential of 125F.(145F-20F)

155F/125F =1.24

I believe the higher temperature boiler would be losing 24% more energy to the outside air than the same boiler at the lower temperature.

The same logic should hold true for underground lines but the soil temperature would be used instead of outside air temperature.

That seems counterintuitive to me given that at either operating temperature the unit will have the same insulation value on the OWB and the underground lines and should lose the same amount of heat.

Where is the physics major when we need one?:monkey:

 

[bnew]

No Im not heeting domestic water. Im just saying that to keep water hotter takes more heat.More heat means more fuel and oxygen.Husky137, Im not saying I made a breakthrough in the "science" of heating homes.I have proven to myself that this saves me a lot of wood and thought people could give this a try to if it helps them.

 

[Al Smith]

In my opinion the whole thing becomes a puzzle regarding heat loss.You have to figure the amount of btu's to raise and maintain the water temp.If it goes from hydronic to air via a coil,that is another factor .If you are heating domestic water via a heat exchanger,that's another loss because heat exchangers are not 100 percent efficiant.

No matter if is is straight hydronic or hydronic to air the placement of the heat outlets,register or radiator is another factor.You have duct losses,line losses and again efficiancy losses concerning types of radiators.Too much for my pea brain to grasp.

 

[joecool85]

That seems counterintuitive to me given that at either operating temperature the unit will have the same insulation value on the OWB and the underground lines and should lose the same amount of heat.

Where is the physics major when we need one?:monkey:

That laws of science tell us that every object radiates heat, the hotter the object the more energy it radiates (to the 4th power).

So it really is a big deal trying to keep the water at 170 compared to keeping it at 140.

 

[joecool85]

In my opinion the whole thing becomes a puzzle regarding heat loss.You have to figure the amount of btu's to raise and maintain the water temp.If it goes from hydronic to air via a coil,that is another factor .If you are heating domestic water via a heat exchanger,that's another loss because heat exchangers are not 100 percent efficiant.

No matter if is is straight hydronic or hydronic to air the placement of the heat outlets,register or radiator is another factor.You have duct losses,line losses and again efficiancy losses concerning types of radiators.Too much for my pea brain to grasp.

It's all a matter of how quickly you need things to heat up. If you want to heat your house up quick, then running a higher temp through the boiler would be required. Same thing with hot water usage. But if you don't use a ton of hot water, and you keep your house at the same temp all the time (and have decent insulation, keep doors closed etc), then running a lower temp would be more efficient and you would still stay warm.

I'm thinking that for most people 160 should be about right, 170-175 if you use a lot of hot water or have lots of people in/out of the house, and down towards 145-150 if you don't run a lot of water and keep your house at the same temp all the time and don't open/close a lot of doors.

Keep in mind this is from a college kid who does not own an OWB (or a house) until (hopefully) next year after I graduate in the spring. I don't have an engineering degree, but thermodynamics is a field I dabble in.

 

[Al Smith]

Well,then you get to the point of cost doesn't justify results.An example could be my hot water heater.Mrs Smith,bless her heart likes water that is about boiling from the tap.Now bear in mind you have to mix cold with it to use but women being whom they are can't be convinced that the extra heat in not efficient.After scalding myself in the shower I think you would almost have to heat water twice to get it that hot.
All this talk is really just rocket science any way.You just have to shove more wood through the thing if you run hotter water.What the heck,good exercise,you get to run the saw,carry ashes,repair the rear window of the pick-up-truck because of inaccurate pitching of rounds into the bed.Lots of things to be said about burning lots of wood.

Just think how many people go to the spa to get toned up.They walk for miles on a treadmill but go no place.Lift weights but don't do any usefull work.Burn wood,you get all that for free plus you beat the utility companies at their own game.Ponder those thoughts.

 

[windthrown]

I have a degree in engineering, and a lot of this is still a mysetery to me. Heat transfer and thermodynamics are a complex subject. I still grapple with the concept of black body ratiation. Some things to point out that I have observed running a CB OWB though:

160 F. is below the recommended threashold for several types of boilers. CB has the lowest setting at 165. I set it at 165 last year, as we have DHW w/ a flat place HX and hydronic foor heating set at 100 deg. off another flat plate HX (hardwood floors and tile). Hydronic (hot water loop) heating varies with floor type, and with pile rugs can go up to 140. In that case, a higher temp boiler loop would be better for a faster/better heat exchange rate. At a 100 degree setting in the floor loop, there is no issue with keeping the boiler at a lower temp. Also with HX there is going to be a 10-20 degree drop between loop and water temp at the other side. We have all the hot water we could ever want here, and it is scalding (140 or more). We also have a pre-heat water tank that has a solar loop in it, so on sunny days the boiler heates pre-warmed water.

However, there is also the issue of stored energy to deal with here. While it may be more efficient to keep the boiler loop temp lower, it may also be more efficient to keep it at a higher temp. Some claim that 180-185 is more efficient, and that is where CB sets their boiler temps at the factory. Also something to consider is that there is less energy stored in that loop at a lower temerpature. Since we all want stored energy on demand for heating, having a higher loop temp will store more energy that will heat your house longer, or at a higher temp (whichever you prefer). I have found that raising the boiler loop to 170 is better for house heating overnight in case it gets colder than expected and the wood runs out by morning. 5 degrees of water heat is probably enough to heat this house for an hour at about 40 degrees outside temp. So if I kept the boiler at 190 instead of 170, I would have 6 more hours of heating time stored in the boiler loop at any given time.

I cannot say if the efficiency is any better one way or the other, as we burn so many different types of wood here and the heat demand varies so much from winter to winter. It ~seems~ to me that the boiler runs better at 170 than at 165. Another factor to consider is that there will be less condensation in the firebox at higher temperatures. But I have researched the corrosive effects of creosote on mild steel and they are quite low. So low that I do not bother to worry about it in our plain steel firebox. It is the water trapped in the creosote and ashes that will do the damage to your steel box. Also the creosote buildup for us seens to be far more dependant on the species of wood burning, and how dry it is. Green conifer creates the most creosote, dry hardwood creates the least.

Central Boiler Classic 4436 here, been in use for 2+ years, and still going great. It does burn a lot of wood, but we have all the free wood to burn in a lifetime here. And we save $300+ a month on heating, using a renewable resource with a low carbon footprint.

 

[fourapples]

Not to change the subject but sticking with OWB tips topic, I want to know what you all do when loading your OWB to safeguard against excessive smoke. I do wait until the fire burns down and there is less smoke, I don't load during forced air heat cycle but by the time I get my wood loaded (dry wood supply) there is a pretty good fire starting and smoke along with it. Do you wear protective mask or something else? Problem is I am using some smaller pcs. of wood from old inside wood stove and it takes a while to load the firebox.

 

[beerman6]

I like to load mine when it's calling for the blowers to be on,no smoke.

 

[windthrown]

I crack the door open for a minute while I go get a log to toss in there before I open the door. The natural convection pumps most of the smoke out the chimney. Otherwise I get a blast of smoke in the face along with gasified unburned wood gas, which is not good stuff to breath in and can flare up at you and singe your hair and stuff. Also we do not have a forced air system. Natural convection does it all just fine.