144k BTU, 3 inch main?

Al Riso

I have an old gravity hotwater heating system. I've got to change the boiler butI want to remain gravity not forced circulation. Existing boiler has 3 inch tappings feed and return with 3 inch main. I can't find a boiler with 144,000 BTU with 3 inch tapping. I would prefer to use peerless. Is there any chance?

Jim Erhardt

Yes....

Just connect from the boiler to the mains with the largest size pipe possible (tapping size in boiler) in the shortest possible distance. Beware of condesation on start-up and on "marginal" days when only a little heat is required; going to forced circulation with primary/secondary pumping makes a lot of sense in these applications. Install a reverse-acting (low limit) aquastat in the primary loop to shut down the system pump when primary loop temp falls too low - a simple yet effective way to protect your new, higher efficiency boiler.

Question - Why were pipes so large on those old gravity systems?

Answer #1 - Back in those days, plumnbers were "real" men!

Answer #2 - At any given flow rate, head loss in a pipe is based on the diameter of the pipe and the length of the run. To achieve adequate flow (based on heat loss and desired d-T) in a gravity system, the pipe had to be "manly" in size. Now where's my 3-inch ratchet threader?

Question - When did the first variable flow rate, weather-responsive hydronic heating systems first appear?

Answer - Back in the days my grand daddy was cutting and threading 3-inch steel pipe by hand! The original gravity systems provided a high level of comfort because of these characteristics. The greater the d-T between inside the house and outside, the longer the thermostat remains closed and the longer the burner fires. The longer the burner fires, the higher the average system temperature. The greater the d-T between supply and return, the greater the flow rate. So today we do with elaborate electronics what a simple control system of a thermostat and high limit did over half a century ago.

Of course, the lack of insulation in homes and the huge water content/mass of the gravity systems didn't make them very ecomomical to operate. This is why when replacing a boiler in a gravity system, you must go beyond the heat loss of the structure. The I=B=R ratings for boilers include a 15% "pick up" factor for BTUs lost to/through the distrubition system. I would suggest selecting the boiler based on heat loss plus another 30% to cover the very high pick-up losses of a gravity system. Your mileage may vary.

Jim Erhardt

Yes....

Just connect from the boiler to the mains with the largest size pipe possible (tapping size in boiler) in the shortest possible distance. Beware of condensation on start-up and on "marginal" days when only a little heat is required; going to forced circulation with primary/secondary pumping makes a lot of sense in these applications. Install a reverse-acting (low limit) aquastat in the primary loop to shut down the system pump when primary loop temp falls too low - a simple yet effective way to protect your new, higher efficiency boiler.

Question - Why were pipes so large on those old gravity systems?

Answer #1 - Back in those days, plumbers were "real" men!

Answer #2 - At any given flow rate, head loss in a pipe is based on the diameter of the pipe and the length of the run. To achieve adequate flow (based on heat loss and desired d-T) in a gravity system, the pipe had to be "manly" in size. Now where's my 3-inch ratchet threader?

Question - When did the first variable flow rate, weather-responsive hydronic heating systems first appear?

Answer - Back in the days my grand daddy was cutting and threading 3-inch steel pipe by hand! The original gravity systems provided a high level of comfort because of these characteristics. The greater the d-T between inside the house and outside, the longer the thermostat remains closed and the longer the burner fires. The longer the burner fires, the higher the average system temperature. The greater the d-T between supply and return, the greater the flow rate. So today we do with elaborate electronics what a simple control system of a thermostat and high limit did over half a century ago.

Of course, the lack of insulation in homes and the huge water content/mass of the gravity systems didn't make them very ecomomical to operate. This is why when replacing a boiler in a gravity system, you must go beyond the heat loss of the structure. The I=B=R ratings for boilers include a 15% "pick up" factor for BTUs lost to/through the distribution system. I would suggest selecting the boiler based on heat loss plus another 30% beyond the I=B=R rating to cover the very high pick-up losses of a gravity system. Your mileage may vary.

Robert O'Connor_6

I'd emphasize

"Beware of condensation on start-up and on "marginal" days when only a little heat is required; going to forced circulation with primary/secondary pumping makes a lot of sense in these applications. "

Leaving a system gravity is very hard on cast pin style boilers.

Somewhere there is a diagram shows how to pipe primary secondary and leave the secondary side gravity,

Search "gravity" and "gravity conversion" in the search feature on this site.

Regards

Robert
ME

Mark Hunt

Gas or oil?


If it's gas, the Weil-Mclain EG series boilers have 3" tappings for the supply and 2.5" on the returns.



Mark H

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