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Author Topic: Draw the water off the top or bottom?  (Read 7047 times)

mlappin

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Draw the water off the top or bottom?
« on: January 21, 2014, 11:10:47 PM »

So spent a lot of time researching gasification boilers on line then found this site to be a wealth of information in one place.

Built my first boiler thats still in use over a decade ago, then built a few for family and friends which I'll never do again as they think they came with a life time service agreement or something.

First boiler is still going strong but have decided I want something more efficient so whence the gasifier.

I found this thread that covered a lot on where to draw your water off, http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=213.0. Was wondering though if since that thread was last active if a new rule of thumb has become accepted? The ones I built I returned the water under the fire box and draw the water off halfway between the top of the firebox and the maximum water level. I seemed to get a very good mix of water in the tank according to a infrared thermometer.

But I'm wondering about any potential problems of pumping cooler water under what will be the hottest part of a gasifier if sticking to the Portage and Main style?

On the ones I built I installed a tee in the supply lines on the back of the water jacket and actually have my thermocouples in the water flow. Problem I could see with this with drawing off the bottom is the water near the top of the boiler could be near boiling then, or would it mix better with drawing the water off the bottom and returning it at the top to the opposite end by the loading door? I've also toyed with the ideal of having a high limit aqua stat near the top to override the normal control if the water was considerably hotter near the top compared to what the pump was drawing. Or even two, one to override the main control if say the water was 200-205 and a second one with a interlocking relay to kill power to the fan and damper if the water actually reached boiling until it was manually reset.

Normally I'd just play around with this and figure it out the best as possible on my own, but it looks like I'll be extremely busy all year and would like to have it done before the next heating season. So any way I could save some time is a huge plus.

Im a farmer by trade and I've picked more ground up for this year plus will have another 40 acres of hay to make this year. Also promised the wife I'd get another room remodeled this winter before I got "busy" in the spring. Happy wife, happy life. ;D


Any help or thoughts on this would be mucho appreciated.
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LittleJohn

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Re: Draw the water off the top or bottom?
« Reply #1 on: January 22, 2014, 06:24:01 AM »

Glad to hear you are building your own good for you.  I totall understand the friends and family thinking they have a lifetime warrenty, have helped a few myself with there radiant systems (in-slab) and now I am the first person I call when they have an issue.

I personally have CB eClassic 2400, it draws off the top and returns to the bottom.  I think it works better because of heat stratification that happens in a tank; even happens in your hot water heater. 

That being said I personally would not draw off the bottom, their is too much chance that you will suck up sediment or such and potentially foul a pump or plug a strainer/HX (assuming you are using one).  Now I know that there are hundred people out there in the forum and they will argue this point back and forth, just my $.02

GOOD LUCK ON BUILD, pictures are always appreciated
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mlappin

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Re: Draw the water off the top or bottom?
« Reply #2 on: January 22, 2014, 07:30:00 AM »

Depending on who it is I just about hate to help some people out anymore, I do good work then they don't take care of it and their negligence is my problem. Not only did I build a boiler for a second cousin I also yanked the original gas motor out of a grain truck for him and installed a Cat diesel in it's place, anything goes wrong on that truck and he calls me.

Anyways, back on track here. If I was to do the bottom thing I'd stay 2-3" off the bottom. The other boilers I built I had the tank completely built but the top wasn't welded on, carried them outside with the forklift and pressure washed the inside out then welded the cap on. I could install a bypass around the snow melter heat exchanger and run around the plate exchanger for the first few weeks until the strainer didn't turn up with any gunk in it. Water heater is just a sidearm so that should never plug.

One thing I do like about the drawing off the top way, I installed a check valve at the bottom of the boilers I built with the theory of if a line ever burst the boiler couldn't completely drain and leave the firebox high and dry. Of course in 14 years I've never had a line problem, will probably install new underground pipe with the new boiler. I have one corner I know I'm losing heat at is it's the first place to be snow free when the temps get above freezing.
« Last Edit: January 22, 2014, 07:34:49 AM by mlappin »
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Re: Draw the water off the top or bottom?
« Reply #3 on: January 24, 2014, 03:37:58 AM »

I built mine and finally got it going last week.     I drew my incoming water off the bottom and return to the top as many others do.

By bottom though I am not on the bottom of the tank.  It is at least 10" up from bottom.  The return line also is not right on the top and extends into the tank 4.5'.

My main thinking was that if I did get a leak in system I would not be running pump dry for quite a while.  Also I thought that it would put more pressure to prime the pump which is in the basement.

A gasifier may be different though.
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lawrencep

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Re: Draw the water off the top or bottom?
« Reply #4 on: January 24, 2014, 07:58:35 AM »

I guess everyone has a opinion on this subject.but I draw off the top because of like your said if a line blew it wouldn't burn up my fire box also the mass of my water is at the top of my boiler. Just my 2 cents
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mlappin

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Re: Draw the water off the top or bottom?
« Reply #5 on: January 24, 2014, 11:44:46 AM »

Since I'll be heating both the shop and the house I've toyed around with the ideal of having one pull off the top and the other pull off the bottom.

I suppose I better pull the trigger shortly and get started on this, then I'll hopefully have some time to mess around with different configurations on the plumbing before welding the top of the water jacket on.

I seen some cheap screw in temp gauges on Amazon, I might even go as far to test each one with boiling water and writing the differential on each one as I can't believe they would all read identical. I have a infrared thermometer but I'm not sure how believable that is.
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Re: Draw the water off the top or bottom?
« Reply #6 on: January 24, 2014, 04:24:14 PM »

Returns at top, supply lines off the bottom
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mlappin

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Re: Draw the water off the top or bottom?
« Reply #7 on: January 24, 2014, 09:51:31 PM »

Returns at top, supply lines off the bottom

Would that hold true for a gasifier as well?
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Re: Draw the water off the top or bottom?
« Reply #8 on: January 24, 2014, 09:53:49 PM »

Returns at top, supply lines off the bottom

Would that hold true for a gasifier as well?


More than likely yes, it encourages a balanced tanknof water all the same temp and helps eliminate potential hot spots
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mlappin

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Re: Draw the water off the top or bottom?
« Reply #9 on: January 24, 2014, 11:14:10 PM »

Returns at top, supply lines off the bottom

Would that hold true for a gasifier as well?


More than likely yes, it encourages a balanced tanknof water all the same temp and helps eliminate potential hot spots

Hmm, I'd like to have the new one in place before next heating season, but if it ran into December or so long as the old one still worked I'd have time to experiment.

Like I already mentioned, get some reasonably priced thread in temp gauges and play around a bit with different pump configurations.

I'm leaning towards if I drew off the bottom in the back of some how returning the cool water to the top of the front.
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renoman

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Re: Draw the water off the top or bottom?
« Reply #10 on: January 24, 2014, 11:20:18 PM »

if you extend your return 2/3 to 3/4 of the way into the tank it will force the water into the front and around to circulate. This is the way my unit is but with my temp gauges I show 190 on the supply pulling from 10" off the bottom with my aquastat set at 195 positioned 3/4 of the way up the tank so there is a bit of difference throughout the tank but not huge.
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Re: Draw the water off the top or bottom?
« Reply #11 on: January 29, 2014, 08:22:53 AM »

Really does it matter pulling top or bottom?   ??? 
I think its more important to have the water circulated around inside the boiler, so one of the ports could basically be a bung on the boiler, while the other should extend approximately 3/4 of the way into the boiler - this will facilitate mixing of water inside the boiler (basically how a Hot water heater works - dump cold water in bottom and pull hot water off top)
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Re: Draw the water off the top or bottom?
« Reply #12 on: January 29, 2014, 08:36:10 AM »

Cold water drops, by doing the return in the top the water in the furnace will naturally mix. Supply should be several inches from the bottom and the return should be in the top and run most of the way to the front.
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Re: Draw the water off the top or bottom?
« Reply #13 on: January 29, 2014, 08:57:39 AM »

On my homemade unit. I pull from the middle. And return at the top. My return lines run 40 inches  into the tank. Had a little boil over and lost over 60 gallons of water,but the pumps were still submerged. If it was the other way I probably would have lost both of my pumps.
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mlappin

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Re: Draw the water off the top or bottom?
« Reply #14 on: January 29, 2014, 10:49:56 AM »

Considering what the boiler costs to buy or build, pumps are small potatoes.

On my original I pulled off halfway between the top of the firebox and the max water level, have swirl destroyers above the supply line so as not to suck air, returned the water under the firebox. Have check valves in the returns at the back of the stove so if a line would ever break couldn't drain the stove. In hind sight the check valves are not needed as never even had a leak in a line or fitting let alone a failure.
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