Draining boiler system

My house has a radiant heating boiler system which I will be removing. I am beginning to drain the system and disassemble the unit. Since this is a continuous system with three zones, there are no release valves anywhere throughout the piping. Therefore, I wanted to ensure the proper method for draining.
On the side of the boiler is a spigot which I know is the main draining point. Though, I question the spigots located on three separate pipes, which I assume is for each zone. Do I need to drain from them as well? Due to suction/pressure in the system, I would think there may still be water even after I drain the main spigot. Therefore, it appears logical to also drain from the other three spigots.
Appreciate any help.
Here are photos of the spigots.
Main spigot on side of boiler >>>> http://www.flickr.com/photos/18223943@N06/7520408048/in/photostream
Three spigots and three zones >>>> http://www.flickr.com/photos/18223943@N06/7520407744/in/photostream /
Closer view of the three spigots >>>> http://www.flickr.com/photos/18223943@N06/7520407908/in/photostream /
Thank you
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Drain the boiler, drain each zone. There may still be some residual left depending on how the tubing is laid out with low spots.
It may or may not matter how well it is drained, depending on what you are replacing it with.
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I wonder if there is some way to pump compressed air in, which will float. The water will be displaced out. Inflate to 30 PSI, and then open the drain. Repeat. I've never done this, just thinking out loud.
Christopher A. Young Learn more about Jesus www.lds.org .
Thank you
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On Sat, 7 Jul 2012 11:07:18 -0400, "Stormin Mormon"

Once the boiler is cut from the supply line, you could put an airline there. It would have to help move some water out.
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When you say removing are you saying that you will discard it you furnace should have drain someplace on bottom of it for drain and spigots use to brake vacuum which yes also may have some water to come out, I have same in my home which I had drain few times to replace circulating pump.

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The three spigot's are used for purging air out of the system when you fill it.
Drain them all. If you have bleed valves on the radiators, opening them will speed things up. It will take quite a while to drain and you won't get all the water out unless you blow it out with air, and probably not even then. You can apply air to each of the "3 spigots" in turn, leaving the main drain open and closing the other two spigots.
It looks like you have a single circulator pump and 3 zone valves. You will want the zone valves open while you drain. Usually there is a manual override, otherwise you will have to jumper the thermostats to open the valves (or setting them to highest temperature may work too).
HTH,
Paul
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