Print

[tawilson1152]

I think my boiling is coming from the water tubes going through the chamber. I am assuming the flow is not enough to prevent the boiling. I've thought about adding a second pump to run when it's on a burn using the extra bungs but need to drain it down. I should have put some valves on last year when I drained it.

[Crow]

  Is it possible that IF the wood is loaded at the front of the stove the water could be much hotter in that area?
Where is the temp sensor on your furnaces? 
  When I load mine I keep the wood close to the door to keep the flame and heat ahead of the baffle in the back of the box. When the temp reads over 193/4 ( sensor is mounted at the rear of the furnace ) I can hear it bubbling. So to me either the temp sensor is not accurate or the water is hotter at the front than at the back?  I dunno?

[mingom]

Sensor is in the back, maybe I've been loading too close to the front?

[Sprinter]

Pressure is what effects boiling point. Like nascar radiators running 56psi and running 280 degree temps with no boiling. Thus the dumb rule on stat limits

[mingom]

Thanks Sprinter - i understand the pv=mrt rule, but i'm not quite understanding what you're saying about my boiler.  It's not pressurized so it should always be equal due to being open to atmosphere correct?

[tawilson1152]

I think we are talking non pressurized systems here and I am sure you know that. I just think when I have a 150 gallon water jacket and a pump doing 7 gpm  there is a chance of a hot spot.

[mingom]

Alright - a little perplexed - went out this AM, temp was low (155)- had eaten through all the wood I had loaded (-8 outside).  I got it roaring again pretty quick, but again - boiling noise but way down at 156.  It must be creating hot spots??

[slimjim]

Mingom, try cutting the air back a bit for a slower burn, constantly boiling water anywhere in your boiler is bad for the boiler.

[mingom]

Sounds good - just can't figure out why it started doing it all of the sudden part way through the season (Dec/Jan).  How would you cut back the air?  Partially cover the blower intake?

[slimjim]

Yes, I think there is a damper plate behind the blower motor where it screws to the door, slightly loosen the screws and slide the plate, use caution loosening the screws as they break very easily

[Sprinter]

Thanks Sprinter - i understand the pv=mrt rule, but i'm not quite understanding what you're saying about my boiler.  It's not pressurized so it should always be equal due to being open to atmosphere correct?

If you goto Calefi Idronics edition wood boilers they have diagrams of how you can achieve boiling under 212 degrees in an open system. I was referring to open systems, since we know increasing pressure raises the boiling point. Open systems are at risk of sub atmospheric conditions because they are not pressurized.

This is especially true when very large pumps are used, or when any part of the system is above the boiler water level.  We understand siphoning right? Well when we pump water uphill it has to fall back down, thus creating a siphon or suction on the downhill side of loop. This suction creates all kinds of problems, sucking air in thru any air vents, valve packings, seals, etc. air can be the gurgling, or when the suction side goes sub atmospheric, ie. reduced pressure, you can get boiling in spots.
Another way is when a rediculously oversized circulator is used.  Our pumps do not pump water at all, they circulate water by changing pressure on either side of the circulator.  Water naturally wants to equalize, and this creates flow. Taco has a video showing this, and exactly how circulators work in hydronics.  The circ itself can cause boiling, also all these OWB's usually have 1" ports, or let's say they have too small a port for the circ and pipe in the application. Well do we understand velocity stacks on carburetors, and the Bournoole  principal. Shoving too much water too fast thru 1" pipe for instance creates positive pressure, now when it enters a large open volume of water there is a rapid change in pressure. Same for the supply side.  Increasing circ speed would increase the issue and slowing it down by speed switch or valve would reduce the symptoms.

These are just some possibilities, you might have a hot spot, but that would have to be one very bad jacket design to do so.  You would have to move much less than 4gpm through a 1" port to not disturb stratification layers in the boiler.  If I had to bet, I'd look at other possibilities like mentioned above.

Just look up the threads I started with all the links to tons of hydronic info

[mingom]

That makes sense - I did upgrade to a 1/2 Hp 3 speed grundphos this fall - perhaps it's causing the issue

[Sprinter]

http://www.radiantandhydronics.com/articles/86249-noisy-pipes

Here's one option