[an error occurred while processing this directive]
Posted by Ken on October 08, 2012 at 12:25:23:
In Reply to: Differential Setting posted by Dan on November 16, 2010 at 19:45:52:
: I have an old steel boiler and is used for heating only--gas fired water boiler. When cycling, supply water coming out of boiler run 170-180 and return 156-160 degrees when measured with a hand held thermometer. Control is a L8054A Honeywell dual aquastat. Adjustable internal limits set at Hi Temp 180, low temp 120, and differential set at 5. Boiler gauge shows internal temp at 175-180 and approx. 22PSI when cycling (12 PSI of cold static pressure). I thought it may improve efficiency to allow the water to cool to 160 before the burner reignites so I bumped the differential up to 20(the max) but it did not change the operation in any way. I can not find a manual on the aquastat which could have been wired wrong when an upgrade to the AC system required a change out of thermostats. Am I misinterpreting what the differential setting is suppose to do? Is 20 degrees differential to much for a steel boiler? I checked the HW site to see if I can find a manual on the controls but they say that is obsolete and don't have it. I have read many of the aquastat post but most seem to apply systems that are used for DHW and heating so I haven't figured it out yet--not even sure why I need a low limit on my system?
ANSWER: the low limit is to protect your boiler. If the return water is much lower than 160 F you may begin to have thermal gradient across the steel coils (cold water into the hot coils) and cause leaks. If you're all ready getting enough heat, don't try this to gain efficiency, it wont work.