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Posted by HeatPro on October 09, 2009 at 10:00:06:
In Reply to: having problems with two line system... posted by johnwayne on October 09, 2009 at 08:09:05:
Many people get themselves into this situation thinking that everything is bigger in Texas and two lines is better than one. The most usual problem is that by converting a one-line system to feed .65 gallons to a water heater and .75 to a heater, the total one-line flow is 1.4 when both burners are on. That runs through a 3/8 line OK at the distance of most houses.
However, when you convert to two-pipe, the flow through the lines is 2.5 gallons or more every time a pump runs and 5 when both run which doesn't squeeze through; making a high vacuum.
Go back to the single line and use tiger loops and you won't see problems for years. After you fill the line that goes to the ceiling with no line leaks, the line stays full and you aren't lifting; it is actually applying height pressure to the pumps when the pumps stop running.
A two-pipe system isn't a cure for an air problem; fixing the air leaks is the proper fix.