OWB below basement level???

[mybowtie]

Does the OWB need to be higher then my water to air heat exchanger?
My plumming guy is telling me that its a open system, and the OWB nees to be higher then the rest of the system.
Or the water will flow to the lowest point, the OWB, and drain out the OWB's overflow.

It's a Woodmaster 4400. I'm not hooking to the DHW, so its a simple loop from the boiler to the water to air coil and back.

The top of the OWB will be about 1 1/2 feet below the water/air coil. Its only 25' from the house, and another 25' run to the furnace
once inside...Woodmaster is telling me no problem.
Anyone having problems with the OWB lower then the house?

 

[Gooserider]

I think you can get away with that small of a height difference, though your plumber is right that it is better if the OWB is higher... There are two basic issues involved...

1. It will be a little harder to fill and purge the system as the high point will be in the HX rather than the boiler, which means that you will have a tendency to trap air in the HX. However 1.5' isn't a huge amount so your pump might be able to push that much air out, or you could do a pressured purge with your regular water supply. However once purged, you won't lose the water in the pipes as long as both are under the boiler water level, for the same basic reason that a hamster bottle works - Any effort to drain would pull a vacuum in the system, which isn't going to work unless there is a source for the makeup air.

2. You may have a problem with bubbles building up at the HX. I would consider putting a good air separator on the supply line out of the boiler, and possibly a positively sealing air vent next to the HX - note that this vent must NOT allow air to enter back into the system when the pump turns off and the pressure at the HX goes negative. You also need to minimize the number of fittings and such near the high points, probably nothing more than the shutoffs on the HX (in case you need to change it out) and make sure there are no leaks anywhere.

IOW it isn't optimal, but the issues can be handled.

Gooserider

 

[mybowtie]

Thanks for the info...So your saying I should keep the supply and return line as low as possible. I was planning on running
the lines along the basement celing, then down to the HX. Would it be better to keep the lines along the floor, which would
keep them much lower then the top of the OWB???

Im planning on using a Grundfos 3 speed 15-58 circ. Which cross ref to a taco 7 or 8.
House is around 1200 sf. Is this circ big enough??

 

[Gooserider]

Thanks for the info...So your saying I should keep the supply and return line as low as possible. I was planning on running
the lines along the basement celing, then down to the HX. Would it be better to keep the lines along the floor, which would
keep them much lower then the top of the OWB???

Im planning on using a Grundfos 3 speed 15-58 circ. Which cross ref to a taco 7 or 8.
House is around 1200 sf. Is this circ big enough??

Unless your basement ceiling is like a sports stadium, :lol: it probably won't make a huge difference, it would just change where the high point(s) are in the system - with the same issues involved. If you have two high points because your both your supply and return lines have high points, it might be worth making sure there is an air vent at each one, again making sure the vents won't let air back into the system when the pump is off.

As to the pump sizing, I can't really say, as you don't give enough information. If you go back up to the "Useful Tidbits" sticky at the top of the boiler room area, you will find a link to a Taco technical paper on how to figure out pump choices and pipe sizing based on heat loads and head loss figures. Cranking through their math is really the ONLY way to ensure that you are doing the right thing for pipe size and pump selection. (BTW, they say you should try to arrange for a fluid velocity of 2-4 feet per second, given your setup I would suggest that it would be best to try for the 4fps end of that range)

Gooserider