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[themaddhatter]

In case you missed it, had discussion about OWB woes here: http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=2211.0

Got a game plan, bits & bobbles coming from 3 online vendors, and am prepping the OWB itself for moving the pumps out there.

Here are my current dilemma:

This is a homemade OWB, and as such, it has no documentation, so you basically "figure it out" as you go.  On the OWB, there are two 1" nipples coming off the side of the water tank, and two 1" nipples coming off the bottom.  When the OWB is full, the two on the side will drain down 45 gallons of water before "empty".  The two on the bottom, will drain down 375 gallons before "empty".  I have torn logic on whether to use the two side nipples as feeds to my pumps versus the two bottom nipples.  One part of me thinks "higher source has hotter water, so use that".  However, the other side of me thinks "Plumbing to the lower source gives you the most water available before the pumps get starved, and provide the most static pressure pushing water into them".

Looking at the outside of the OWB, there is literally only 6" of vertical difference between the "side" and "bottom" nipples.  I wish I had superman vision, because to me, there must be some sort of syphon tube setup on those side feeds if only drain down 45 gallons vs the 375 of the system.  I may also have another thing to consider here: Bernoulli.  If I only have 45 gallons of water pushing into those side nipples, I don't know if I have enough static pressure pushing the water into the pumps (since I am moving from inside to outside on these things).  But, if I plumb the pumps to the bottom nipples, then we are dealing with a heck of a lot more water pushing down.  Plus, faster drain downs (since the pumps can drive most of it out, rather than gravity alone).  The vertical distance from the side nipples to "full" level is ~ 5.5'.  The bottom ones are ~ 6'. 

The last caveat to this install is that the bottom nipples will allow me a decent straight shot into the pump, then into the PEX going underground.  The two side nipples are facing in weird directions (one @ 3 o'clock; one @ 7 o'clock), so I will have to put a 90 (or a pex bent into an arc), a section of pipe, then pump, then 90, and maybe also arc the PEX before it goes underground.

So.... thoughts?

Cliff notes:

- 2 side fittings with 45 gallons of head; 2 bottom fittings with 375 gallons of head: which fittings would you hook circulator pumps to?

[jerkash]

My OWF calls for top (higher) ones to be used for outlets and the bottom (lower) ones to be used for the inlets.  I believe the reason was because the hotter water is at the top.  If your pump is below the water level the gravity will get it to the pump.  You don't need pressure to get it to the pump.

[shane g]

I have heard of people do  it both ways i would think if you return it at the top it would get the water you are returning back up to temperature quicker just as long as the bottom ports are off the bottom where it wont pick up any sediment off the bottom i think this is how i am going to plumb mine if i ever get the welding done and get it to the house

[RSI]

Using the bottom fittings is a lot better for your pump. I think it keeps the water in the tank mixed better too.

[HandyMark]

Mine calls for the upper nipples to be used as the outlets but if I am running the pump 24/7 so I doubt there is a lot of temperature variation in the tank. I do like to idea of using gravity to assist the pump.

[benj1975]

I ran my pump of the bottom one for the pressure helps move the water and it has been working great so far.

[paperman]

When building mine I plan to place the pumps low but have a stand pipe inside to bring the suction up off the bottom.  My reasons are two fold.  With it off the bottom if you ever lost a pipe in the house you only empty a % of the total in the furnace.  Also if you lost water you would not distroy the furnace from pulling the water down below the firebox.  You maintain the head pressure on the pump by their physical placment not from the point they draw water.  So long as the suction pipe is flooded the head the pump sees is the same as if it were tapped straight into the water jacket. 

   

[dwneast77]

My CB2300 draws water from near the top and returns are about 2' from the bottom.  Pumps are actually located about equal to return height.

My WD HE10000 draws water from about 2' off the bottom and returns at the top.

6 of one, 1/2 dozen of the other, I guess.

[JMA]

Keep in mind, heat rises! But also, alot of furnace bottoms fail from condensation in the fire box because the bottom is to cold. So what do you do? All the manufacturers I know of use the top for the supply and the bottom for return. I guess every stove is different, some may last longer if you draw heat from the bottom, keeping the floor warmer.

[dwneast77]

 One thing that needs to be considered  here is the difference between a gasser and conventional boiler.  A conventional boiler has the hottest heat transfer at the top of the stove.  A gasser has the hottest fire at the bottom in the combustion chamber.  Just a thought to ponder into the equation.