Ok. I'm looking to build an outdoor wood boiler on the very cheap. I have acess to a very large junkpile that an old farmer owns. There is a good deal of 1/4" steel plate (enough to make like a 30x30x30" firebox), and an old Weil Mclain oil boiler. I was searching on the site and read of someone making a firebox be the source of heat for an oil boiler (versus the oil burner), and used the boiler as the heat exchanger. The boiler I believe doesn't leak. Any other ideas for a quick, cheap, and easy to build outdoor boiler? It wouldn't need to be for a lot heat; just to supplement the ground source heatpump I have (warm air). I'd use baseboard heat with it.
Homemade Boiler
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mga
wandering
i have some questions about outdoor boilers:
do they use some sort of relief valve in case they boil over? what is the pressure setting for that valve?
do they use a circulator pump to move the water? what happens in a power failure when the water can't move?
if using baseboard heat and the themostat doesn't call for any more heat, what happens to the water sitting in the boiler? or is it a constant on type of thing?
i've read alot here about outdoor boilers, but i haven't seen any discussion on boiler safety features. i have hot water baseboard heat in my home (gas fired) and i know everything needs to be in working order.
do they use some sort of relief valve in case they boil over? what is the pressure setting for that valve?
do they use a circulator pump to move the water? what happens in a power failure when the water can't move?
if using baseboard heat and the themostat doesn't call for any more heat, what happens to the water sitting in the boiler? or is it a constant on type of thing?
i've read alot here about outdoor boilers, but i haven't seen any discussion on boiler safety features. i have hot water baseboard heat in my home (gas fired) and i know everything needs to be in working order.
Butch(OH)
Addicted to ArboristSite
mga said:
Most operate under 212 degrees and are not pressurized thus they are not boilers per say but hot water heat. The "boiler" is self contained for temp control meaning it is set to come on at X water temp and off at X temp. Mine is on at 160 and off at 170. If the house isn't calling for heat the water simply circulates. When the thermostat in the house calls for heat it draws from the lop and cools the boiler temp. How exactly it draws that heat differs with your heating system, With my forced air heat I have a heat exchanger in the hot air plenum and the house thermostat controls than blower fan. They do depend on pumps to send the heat where you want it and thus when you loose power you loose heat to your house. Also when you lose power the draft door will close shutting off oxygen flow to the fire. The exact events that follow I am not sure of because we have not lost power since ours has been operating. I suppose that it depends on what is going on at the time power goes out. Someone with more experience will have to answer that. My dealer told me that at the worst case it may boil over and you loose some of the water but not all of it. It took about 15 minutes for mine to fill from empty.
mga
wandering
thanks, butch. i wasn't sure how they operated being called boilers. i guess your explanation makes sense.
so, having a generator on hand is a must with an outdoor boiler...correct?
one more question: you stated that it opens a damper door when it calls for heat. what keeps the logs burning if the damper door is closed for an extended period of time?
so, having a generator on hand is a must with an outdoor boiler...correct?
one more question: you stated that it opens a damper door when it calls for heat. what keeps the logs burning if the damper door is closed for an extended period of time?
Butch(OH)
Addicted to ArboristSite
mga said:
Sorry about this hi-jacking your thread Hamradio
If you go to the manufacturers websites they all have good explanations of how the whole deal works. Do a search for Woodmaster, Central Boiler, Heatsource one, Heatmore or just punch in outdoor wood boiler.
Mine is a Woodmaster and it has had a fire in it since Sept so I am not the most experienced. The firebox coals stay warm enough to reignite. I am not sure how long it would stay warm enough but with some warm weather we has a week ago mine was more or less off for several days and re-lit when called upon I suppose by some air leakage and the air I let in twice a day just to check things out. I do not have plans to run mine in the summer so I don't figure to have any problems keeping it lit. I already had a 4500 watt genny on stand by. If a person had to buy one just for the boiler the smallest one made would run several of them. My measured usage is just over a 100 watt bulb or 1.5 amp @110 volts with two loop pumps running and the draft fan. So far I see no minuses to a outdoor wood boiler, some see differently as you can read about in other threads here.
windthrown
361 Junkie
Some OWB questions answered
To answer some of your questions about OWB operation and safety... we have a Central Boiler (CB) that we installed here late last year. CB uses an open-atmosphere no-pressure system, which is safer than a pressurized system. The OWB pump is always on and circulating the hot water from the boiler to the house. The boiler lines run to a pair of heat exchangers (HX); the first is on the hot water heater and the second is on the pressurized hydronic floor heating loop. The HXs isolate the boiler water loop from the house water suppy and the floor loop water.
The OWB controler uses an aquastat to sence the temperature of the boiler water. CB has a controller that will keep the temp within 10 degrees of the set temperature. I keep ours at 165 F. If it gets to 165 it shuts the damper door, and then usually goes up to about 170-175 F. The temp drops over time as heat is absorbed by the hot water heater (HX in a passive convection loop) and by the thermostat controlled hydronic floor heating loop. Once the OWB water gets to 155 F the damper door is opened, the fire restarts and the cycle is repeated.
In the advent of a boilover, the CB OWB just spills steam and water out the top of the boiler unit. It dribbles harmlessly over the side. The OWB is outside, so there is no issue of overboil water flooding anything. Our OWB boiled over a few times last year due to a faulty damper mount (replaced by CB for free). The overboil steam takes a lot of energy with it and the boiler usually cooled off to about 185 F right after the boilover.
We do not have LP gas or natural gas here. So before we installed the CB OWB, our water and house heating were heated by electric-only. So if the power goes out now we are in the same boat here as before. In the case of a power failure on the CB OWB, the circulation pump stops and it stop sending hot water to the house. The heat in the lines just dissipates. The CB also has a solenoid that opens the damper door in an upward position when it is turned on. So when the power goes out, the damper door automatically closes and shuts the fire down. So it is pretty fail-safe. For that reason CB has a UL rating.
You could hook up an OWB to a generator pretty easy. We have a generator here, but I do not have it hooked up to the OWB. We have a good power company here and the power rarely goes out for more than an hour. Our OWB has its own pump for circulating the heat to the HXs inside the house. I would have to power the OWB and its pump, as well as the separate floor heating pump in the house with the generator. Easier to toss a few logs into the fireplace for short term heat.
As for when the damper is closed in an OWB, there is enough heat in there to keep the coals smoldering when the air is cut off. When the damper opens, the air hits the hot coals and the fire ignites. If the wood in the OWB burns out overnight, there are always enough glowing coals in the ash pan to restart the fire when I toss more logs in there in the morning. So restarting the fire is rarely an issue. We have a passive air supply OWB, though CB sells a fan-driven draft system if one is required. A passive air supply is fine for our needs. We also opted for the mild steel option as opposed to stainless steel. Stainless is a lot more expensive and is a worse heat conductor than mild steel. CB uses a corrosion inhibitor in the water to keep the water side of te steel in the boiler from rusting out.
One thing that you did not ask, but you might wanna know... most OWBs do not use antifreeze. For several reasons. One is that the boilers typically have more than enough water to keep them from freezing solid and cracking. Anitfreeze lowers the heat tranfer rate of the water (makes it a worse heat conductor). Also most OWBs are always pumping water through the system. Thus in the case of a dead fire and very cold temps, the heat transfer in the HX system will reverse and the heat in the hot water heater water will heat the water in the boiler loop, thus keeping it from freezing. You can use antifreeze, but do no not use auto antifreeze (ethylene glycol is poisonous). Use propoylene glycol instead. BTW: both of these taste good (yep!), so keep them away from kids and animals and out of the vodka drinks.
To answer some of your questions about OWB operation and safety... we have a Central Boiler (CB) that we installed here late last year. CB uses an open-atmosphere no-pressure system, which is safer than a pressurized system. The OWB pump is always on and circulating the hot water from the boiler to the house. The boiler lines run to a pair of heat exchangers (HX); the first is on the hot water heater and the second is on the pressurized hydronic floor heating loop. The HXs isolate the boiler water loop from the house water suppy and the floor loop water.
The OWB controler uses an aquastat to sence the temperature of the boiler water. CB has a controller that will keep the temp within 10 degrees of the set temperature. I keep ours at 165 F. If it gets to 165 it shuts the damper door, and then usually goes up to about 170-175 F. The temp drops over time as heat is absorbed by the hot water heater (HX in a passive convection loop) and by the thermostat controlled hydronic floor heating loop. Once the OWB water gets to 155 F the damper door is opened, the fire restarts and the cycle is repeated.
In the advent of a boilover, the CB OWB just spills steam and water out the top of the boiler unit. It dribbles harmlessly over the side. The OWB is outside, so there is no issue of overboil water flooding anything. Our OWB boiled over a few times last year due to a faulty damper mount (replaced by CB for free). The overboil steam takes a lot of energy with it and the boiler usually cooled off to about 185 F right after the boilover.
We do not have LP gas or natural gas here. So before we installed the CB OWB, our water and house heating were heated by electric-only. So if the power goes out now we are in the same boat here as before. In the case of a power failure on the CB OWB, the circulation pump stops and it stop sending hot water to the house. The heat in the lines just dissipates. The CB also has a solenoid that opens the damper door in an upward position when it is turned on. So when the power goes out, the damper door automatically closes and shuts the fire down. So it is pretty fail-safe. For that reason CB has a UL rating.
You could hook up an OWB to a generator pretty easy. We have a generator here, but I do not have it hooked up to the OWB. We have a good power company here and the power rarely goes out for more than an hour. Our OWB has its own pump for circulating the heat to the HXs inside the house. I would have to power the OWB and its pump, as well as the separate floor heating pump in the house with the generator. Easier to toss a few logs into the fireplace for short term heat.
As for when the damper is closed in an OWB, there is enough heat in there to keep the coals smoldering when the air is cut off. When the damper opens, the air hits the hot coals and the fire ignites. If the wood in the OWB burns out overnight, there are always enough glowing coals in the ash pan to restart the fire when I toss more logs in there in the morning. So restarting the fire is rarely an issue. We have a passive air supply OWB, though CB sells a fan-driven draft system if one is required. A passive air supply is fine for our needs. We also opted for the mild steel option as opposed to stainless steel. Stainless is a lot more expensive and is a worse heat conductor than mild steel. CB uses a corrosion inhibitor in the water to keep the water side of te steel in the boiler from rusting out.
One thing that you did not ask, but you might wanna know... most OWBs do not use antifreeze. For several reasons. One is that the boilers typically have more than enough water to keep them from freezing solid and cracking. Anitfreeze lowers the heat tranfer rate of the water (makes it a worse heat conductor). Also most OWBs are always pumping water through the system. Thus in the case of a dead fire and very cold temps, the heat transfer in the HX system will reverse and the heat in the hot water heater water will heat the water in the boiler loop, thus keeping it from freezing. You can use antifreeze, but do no not use auto antifreeze (ethylene glycol is poisonous). Use propoylene glycol instead. BTW: both of these taste good (yep!), so keep them away from kids and animals and out of the vodka drinks.
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