OWF installation on a grade

[runningmike]

I'm in the middle of my install and I went for a walk tonight to run the dogs and clear my head. Of course I spent the time thinking up things I might be doing wrong! Today's hand-wringer is this: My home is on a pretty good grade so the furnace placement out back has the top of the water jacket vent 5 feet (or so) *below* the highest point where my heat exchanger is located. In an open system I think I might have a problem here with the system draining out. The easiest solution I could think of is to extend the vent pipe that 5+ feet so we don't have the drain problem. Thoughts? I'm installing a Woodmaster 4400 with a 80 ft run to a water-to-water heat exchanger supplementing/replacing an oil system.

Mike

 

[Johnny Ringo]

It can't drain out......at least if your thinking what I think you thinking the water will not drain out because of the vaccum it would create......I think your good to go

 

[runningmike]

OK, thanks!
My follow-on question then is why won't it overflow the vent when I'm trying to fill it. My Woodmaster rep said the same thing: It can't drain out. But his reasons-why don't make sense to my amateur engineer's brain. I guess we'll see what happens!

 

[Johnny Ringo]

My installation recomended that I fill it from the house, I put a (spigot/garden hose connector) on both ends of my heat exchanger with valves so I could flush it out with some cleaner if need be. anyway I connected my garden hose to that, open the valve first on the supply, ran it for ten minutes or so then closed that valve and opened the other filling in the return direction. That fills the system and gets the air out.

 

[runningmike]

How big is your heat exchanger? Doing this would fill my HE in about 30 seconds....or you're filling everything except the HE...that must be it (good idea though with the clean-out setup).
In any case, my installation recommends a similar filling procedure with an inline filter and fill valve assembly located on the return line near the HE. My question though pertains to my furnace being downslope from the house...the top of the vent is 5-6' below the topmost point in the plumbing at the heat exchanger. As I see it, when I try to fill the system, it will do OK up until the water level hits the top of the vent and then will start to drain out there, not traveling back up the hill in the supply line.

 

[Johnny Ringo]

once the water level in your owb is above the supply and return lines your heat exchanger will not drain back into the owb. It would need to suck air from somewhere and it can't do that. Like putting a finger on top of a straw and pulling it out of the glass, or think of it like your loop to the house is a siphon hose and both ends are under water in the owb. Your good.

 

[runningmike]

I get it...thanks!

 

[BrownianHeatingTech]

Actually, there's air dissolved in water. While it would take a leak to add air to the line, directly, the dissolved air will come out, and can easily air-lock the heat exchanger. Raising the vent pipe would work, although it could end up freezing near the top, where the water column is further from the heat of the boiler.

I would suggest that raising the vent is certainly worth a try, though. If you can keep the heat exchanger flooded, life will be much simpler. An automatic air vent of some sort at the heat exchanger will help to release any dissolved air that does bubble out of the water.

Joe