Water Jacket Question

histotech

<span style="text-decoration:underline;">Background</span>

I have a Weil Mclain Gold series oil burning furnace. Until January it was used year round to produce hot water and steam for the winter. In January we completed and attic renovation and added a Bosch tankless water heater for hot water and forced hot air for the attic. We now only need the steam for the winter.

I disconnected the wires from the water jacket to the electrical box on the furnace. I wanted to be able to use the water jacket in case the tankless system went down.

<span style="text-decoration:underline;">Question</span> 

Should I drain the water out of the water jacket, or leave it in there? I was thinking that if there was no water in the jacket, the steam might build up faster? Would it damage the water jacket by being empty?

Kevin

jpf321

shutoff valve?

do you have a water shutoff valve between the boiler and the water tank? that's how mine is piped.



I emptied mine...but I'd like to know the answer .. I figured they are manufactured and sold empty so that wouldn't hurt it :-)

histotech

Responce

With my system the water jacket is in the boiler. When ever we needed hot water, the boiler would fire up (before the tankless system). It would periodically fire to keep the water hot.

jpf321

oh ..

oh .. you had a "tankless coil" inside the boiler .. which is also called "tankless" and why your terminology is confusing .. leaving the water in there creates more thermal mass that needs to heat up .. but also holds more thermal energy during cool down.

jpf

Unknown

Danger! Be Careful!

Be very careful how you "shut off" the water heating coil in your boiler. If you trap water inside, this water could turn to steam and not having a way for the steam pressure to escape, the pipe could explode!   Keep in mind - A cubic inch of water makes a cubic foot of steam!   Make sure the water line going in and out is drained and kept open to the air so that any pressure build up is able to escape - Rod

jpf321

oh boy ..

i hadn't thought of that Rod .. thanks .. I have editted the above post making no mention of the danger points previously stated.



but i am a bit confused .. i have a tankless coil .. if the water does become steam where does it currently vent? out my faucets (presumably closed) or out to the street creating a little bubble up in the reservoir?

Unknown

Steam in the Water Coil

Generally this isn't a problem as the water in the boiler doesn't go over 212 + degrees and the water in the coil is pressurized (so you won't get flash steam)  and the coil water is also exposed to the cooler water in the exterior piping which keeps it a degree or more below the temperature of steam and so the H2O in the coil stays in its the liquid form.



In some places the "code" requires a T& P relief valve on the piping like the one that is on a water heater. That's what I have on mine and it makes good sense to have one whether it is "required" or not.

The danger comes when there are shut off valves on the pipes going into the coil. I have them on mine and also a drain valve (on the boiler side of the shutoff valve) which I open and leave open when I shut the steam boiler down in the summer.(We go to an electric WH then)  The pressure relief valve is on the boiler side of the valves so if the drain and line valves are closed accidentally and the boiler was turned on, there would still be protection  - Rod

jpf321

understood .. thanks...

i realized driving home tonight that the water pressure is ~90psi from the street so it takes higher temp to steam it...

histotech

Thanks

I will close off the shut off valves going into and out of the water jacket, and drain it. Thank You for your responces.

Kevin

Unknown

Water Coil Shut off

It's VERY important  that the pipe between the boiler and the shut off valves to be open to the air so it can drain/relieve any pressure build up. If one of the shut off valves leak, you could get water in the coil which could then turn to steam and build up dangerous pressure. If for any reason you have any doubts, call a professional! - Rod

Big-Al_2

Immersed?

If the coil is immersed in boiling water, then its temperature can never be higher than the water in the boiler . . . and thus the resulting steam pressure can never be higher than that in the boiler.



However , , , if the valves are closed and there is no air in the coil, pressure could build just from expansion of the incompressible water as it heats up.  That wouldn't create an explosion, but it might be enough to crack something.



OT: Where I have heard of a problem is soldering a closed ball valve with water trapped in it.  It could reach several hundred degrees and come apart with a big bang and plenty of shrapnel.  I once tried to loosen a rusted tight brake hose from a front brake caliper using heat near the fitting.  The rubber hose broke down from the heat, built pressure, and literally exploded from under the crimp sleeve . . . nothing seriously damaged except my shorts . . .

Unknown

Better to be Cautious

Hi Al- On a lot of boilers the coil is very close to the surface level of the boiler water or partially above it. That's why  manufacturers recommend you raise the boiler water level during the summer when the boiler is used to only produce DHW. In normal operation the watercoil is filled with water under pressure from the domestic water system which depending on the pressure, won't boil till it reaches a much higher temperature (50 PSI = 281F, 75 PSI = 308F) and since this temperature is much higher than is normally is available from the water or steam in the boiler, there isn't a problem.

 My concern was that if the shutoff valves partially leaked and filled the coil over time with non pressurized water, this water might be flashed to steam when the coil was exposed to steam as the boiler water level dropped during steam operation. When working with steam I always keep in mind that 1 cubic inch of water equals about 1 cubic foot of steam so the ramifications of enclosing water and heating it can be scarey!

I guess having been exposed to many weird  "pants endangering" situations over the years has made me very cautious - Rod

Big-Al_2

Still:

By your own logic, in order to pressurize the coil with 50 PSI steam, it would have to reach 281 degrees.  That could never happen if it was inside a boiler full of 212 degree water OR steam.  The boiler would have to get up to 50 PSI or be dry fired.  If that happens, the coil would be the least of your worries.



In order for water to flash into steam, it would have to be at a low enough pressure to allow it to boil, basically the same pressure that the boiler is at.  If it were even 1 PSI higher, it would and could not happen.  I'd drain it anyway, but I can't think of a possible scenario that could produce high pressure steam and risk a problem.



BTW: The reason that the coil should be immersed in the summer is for heat transfer.  Since there is no available latent heat above the water line unless the boiler is steaming, and since air is a realtively poor carrier of heat, the coil needs to be underwater to get the full benefit of the surrounding temperature.

Unknown

Be cautious

Hi Al- I agree with you that it normally isn't likely to cause a problem however since a lot of places require you to put a T&P safety valve on this line I think it makes sense to follow this philosophy. - Rod