Some problem I've had using a wood boiler to heat my house.

[Richardin52]

I wanted to go over some problems I’ve had in the last nineteen years of heating with my old memo and see if the new boilers out there have any ways to avoid the same problems.

The number one biggest problem, bar non, by far, top of the list, without a doubt is when the power goes out and the boiler is full of wood.

This has happened a number of times and if I’m awake when it happens I just wire my little 600 watt Honda generator to the circulator and away we go - But - several times it has happened when everyone is asleep, then things get interesting. First if it just blows off then my little Honda is not big enough to run the water pump to recharge the boiler and bleed the lines so in the word of Confucius, I was screwed, so I got a large generator.

Then there was that time that the power went out an hour after we it the sack. Of course it was a cold night, It always happens on a cold night, trust me on this one. I had just fill the boiler before I went to bed, it takes about an hour for it to really get up to cruising speed and by that time the whole crew was comatose.

Next morning I got up to go out to fill the boiler and low and behold the boiler room is cold and the inside of the boiler is as white as snow. And there is still some coals in the thing. Apparently the boiler blew off but there was still plenty of wood left in the thing so she just kept right on cooking then the plug located over the fire melted and what water there was left in the boiler hit the fire. Did I mention that I had filled the boiler full of seasoned hard wood? Well the small amount of water that hit the fire was akin to a ten year old peeing on a camp fire, make for a little fun but won’t hardly slow the thing down. So my boiler turned into a wood stove that night and kept the boiler room nice a toasty I’m sure but that don’t mama warm in the bedroom if you know what I mean. So here I am with a cold boiler and no way to get it started. Time to call the Heating contractor and offer him you first born if he will plug that hole ASAP.

The way to fix this problem and I have been meaning to do it one of these days is to get an inverter, one big enough to run the circulator and a small battery bank. No fuss no muss the thing would work great and come hell or high water the boiler would just hum along.

Anyway enough of my rambling. Do you still need to worry about the power going out of a Tarm or Eko or these other new boilers and if so what happens when the water hits the ceramic in these boilers? I’ll bet it ain’t pretty.

 

[smangold]

WE had this happen to a buderous we had when I was a kid. Only the thing cracked in half. My plumber tells me now a thermosyphoning loop would help dump the excess heat, although I couldn't tell you how to plumb one. Also if your using a gasifier with storage you just could burn it at 5:00 and go to bed when it is pretty much out. At least that is my limited understanding.

 

[leaddog]

I had the power go out last week after I had filled up my eko80 and hour before. It was going real strong when the power went out. I watched it and it went up to about 210 and then droped back down. It was thermo syphening into the storage. I wasn't sure how well it would do that as the pipes are only about 18in above the boiler but it seemed to work. It stayed at about 200 untill the power came back on in an hour. But my heat ex. pipes are 1-1/2 so I had a good flow.
When I go to propane tanks I'm going to make sure I keep large pipes going to the tanks and because the tops will be quite a bit higher than the boiler I shouldn't have any problem.

 

[Kemer]

I'm installing mine with a AUTOMAG valve and a siphon loop.If power goes out the valve opens

 

[jebatty]

The "easy" solution is to have an overheat loop, gravity fed (thermo-siphon), sized to handle the heat output in the event of a power failure. I have a Tarm, and the recommendation is capacity no less than 10% of the rated boiler output. This is controlled by a normally open valve (Automag zone valve) - with power on, valve is closed; when power fails, valve opens.

You also need to make sure that when power fails the boiler still is not drawing combustion air, because if it is, the boiler likely will continue to overheat and worse. My Tarm has a forced draft, so when power fails, the air supply also shuts down.

A properly sized UPS also would work, but you likely will need to add battery capacity sufficient to power the boiler/pumps etc. long enough to handle the load of wood. Most UPS systems are not designed to provide power for long periods, so even with added battery capacity, the UPS could be over-loaded and shut down. Test the system to make sure it works when you need it.

 

[cricco]

My system (Newmac BC160 Oil/Wood combo) is setup with a gravity fed loop wich is mounted to the ceiling above the boiler. It encompases 36 feet of baseboard type fins. This is controlled by a circulator pump, which is activated if my temp reaches 200. If my power fails there is a second line that feeds this loop which is controlled by a normally closed zone valve. When the power is cut off, this valve opens and sends water through the 36 foot loop. So far I have had no problems with overheating. My system is also setup to use my garage heater as a dump zone with the power on, so as soon as the power returns, if the system is still too hot, it will send heat to the garage and the dump zone loop.

 

[jebatty]

If your overheat loop(s) is adequately sized and operating properly, your boiler should not overheat. Something is not what it should be.

 

[tire man]

I have a valve which is closed when the power is on and open to dump the heat in one of my larger zones in the house when the power fails. The power failure also cuts off the air supply. With 2 kids under 2yrs, we have a Honda 6500w to power most of the house when we get it going.

 

[Redox]

Reading between the lines here, but I venture he has a conventional OWB without an overheat loop. I would also think that it might be impossible to add an overheat loop outdoors, unless he glycoled the system. Perhaps the best bet is one of those cheap high frequency inverters and a big 'ol deep cycle battery to keep the circ running until the fire goes out. If you shut off the draft fan, how long does the fire burn?

Chris

 

[chuck172]

How do you figure the size of a over-heat loop?

 

[jebatty]

Tarm dealer advise me to size the overheat loop at 10% of the btu rating of the gasifier. Mine is 140,000 btu's, and my overheat loop is slant-fin 32'. I think finned baseboard elements are rated at 500 btu's/ft.

 

[chuck172]

thanks jebatty

 

[BrownianHeatingTech]

Baseboard elements are rated based upon temperature and flow.

Without a circulator to move the water, the flow will be on the low side, so that needs to be accounted for if you are doing a gravity loop.

Joe

 

[jebatty]

Joe - my understanding of advice from Tarm was that the 500 btu/ft was gravity flow. Maybe you have more helpful info. Thanks.

 

[wtom24]

My system has propane tank storage and flow to and from the storage tanks is purely gravity using 3" supply and return (scrounged piping), so a power failure is a non-event.

 

[Mainewood]

Follow the link below and scroll to the bottom of the page for diagram of what you have been talking about.

(broken link removed to http://www.mainewoodfurnaces.com/DO_Installation.shtml)

 

[chuck172]

If the power goes out, the automag valve opens. What if the circulating pump fails, but the power is on? The automag wouldn't open and the hot water wouldn't circulate. Then what?

 

[Eric Johnson]

You can always envision a worst-case scenario that you can't engineer around. You could put a backup pump on the system that would kick on if the temp exceeded the setpoint of the aquastat--say 200 degrees. That would solve your problem.

Overheating your boiler isn't the end of the world. What should happen is the pressure relief valve would open, allowing cold water from your feeder line to cool things off. If you're worried about your relief valve failing, put in two. They only cost about $15 or $20 each.

You could get hit by a bus crossing the street. But I bet you don't spend a lot of time worrying about that.

 

[BrownianHeatingTech]

If the power goes out, the automag valve opens. What if the circulating pump fails, but the power is on? The automag wouldn't open and the hot water wouldn't circulate. Then what?

Wire an aquastat in series with the valve. Use a "break on rise" aquastat, set to 200 (or whatever high limit you want). If you hit that temperature, the aquastat will open its switch, cutting power to the valve. Basically, you use the aquastat to simulate a power failure, as far as the valve is concerned.

Joe

 

[chuck172]

I see the honeywell L4006A1678 100-240 degrees. Contact breaks on temp rise.
Wire the Automag valve in series.
Yes.
Now if the boiler temp rises to set degree (200) -(pump failure) -Aquastat switch opens cuts power to automag, valve opens alows gravity flow.
If a power failure, I assume the aquastat will break its contacts (open) In other words contact breaks on no power. Correct?

 

[BrownianHeatingTech]

I see the honeywell L4006A1678 100-240 degrees. Contact breaks on temp rise.
Wire the Automag valve in series.
Yes.
Now if the boiler temp rises to set degree (200) -(pump failure) -Aquastat switch opens cuts power to automag, valve opens alows gravity flow.
If a power failure, I assume the aquastat will break its contacts (open) In other words contact breaks on no power. Correct?

The contacts are purely mechanical, so they don't break on a power loss, but the power loss, itself, will open the valve, regardless of the contact position.

Joe

 

[chuck172]

Thanks Joe, I'm a steam-fitter by trade. Control work is a little tough on me.

 

[jebatty]

I asked myself the same question and came to the same solution. The Automag is 24vdc, so the aquastat contacts cut the dc to the valve on temp rise. I have mine set at 210, and it is a surface mount on the boiler supply line.