Main vent placement

Steve_175

I have heard hear before that the ideal place to put the main vents is about 3' back from where the return drops. What about putting the main vents just after the last riser? Some loops have quite a few feet of pipe after the last riser and I do not see the need to fill that part of the main quickly when it is in a sense just a drip return. This might also reduce the number or size of the vents needed.

Your thoughts?

nicholas bonham-carter

Main vent placement

There is more headroom at the end, and when you are doing some diagnostics later, the closer location can be more convenient.

You ares hold get enough main venting capacity to achieve a certain low resistance to the escape of air ahead of the steam. You can see this as back-pressure of 1to 2 ounces on a good low-pressure gauge. The Hoffman radiator vents will have a slightly higher resistance to the air coming out of them, and so there will be no steam rising to any rad before the main is filled.--NBC

Rod

Main Vent Location

Just after the last radiator lateral will work fine. Fifteen inches back from the end of the main is the normal criteria however you'll see a lot of systems where the vents are located right at the end of the steam main. Having them located there makes them susceptible to being hit by slugs of water traveling down the main so mounting them forward of that helps eliminate this potential problem.  Unless there is another 20 feet of main after the last radiator lateral or a long dry return with the main vents located at the end of that, you won't reduce the needed vent capacity by much. With the main vents it is better to think over sized venting anyway.

- Rod

TomH42

Just double checking

that the placement of my main vent is appropriate. The vent comes off nipple and then back 18 inches. The nipple rises off the return line drop back to boiler. Is this appropriate?