Gravity Hot Water Conversion to Circulation

Aaron Clark

I have a gravity hot water system that we would like to convert to a circulation system. I have 2 2" pipes that come off a tee off the header of the boiler, which happens to be 2" also. According to the Golden Rule book, I take half the size of the header pipe, and then go down one pipe size..which if my calculations are correct that would be 3/4". My real question is that the radiation load is 137,000btuh's and if I size my boiler to that, and only make my header 3/4", won't the burner (oil) short cycle alot?

John@Reliable_4

Are you sure about.............

radiation load is 137,000btu's? Must big a BIG house.New system would need by-pass piping and other controls to really enjoy the benifits. Would be wise for a pro to size and repipe Hope this helps

Aaron Clark

Thanks but But that's what I do

but after talking to my rep from the supply house he has me thinking, although a myself and a great dead man, my old supply house rep, designed this back four years ago, just what my rep said to me is whats making me unsure, the boiler I am using is a Buderus G215/4, and thier Ecomatic R2107 outdoor reset control. The 215 has a by-pass type return system in it, otherwise I would use a by pass or even a mixing valve, but the radiation size is correct. Just questioning 3/4" with 137,000btuh's. --Thanks!

Boilerpro_3

What's your calculated heat loss?

You could be describing my own home! I had 900EDR of gravity hot water radiation in the house proper, with about another 100 in the garage. Depending whose numbers you use that is either 150,000 btu/hr or 180,000 btu/hr of radiation capacity. The current heat load is about 52,000 btu/hr. So I only need about a 75,000 input boiler and I have been running 90,000 for the past 3 winters. BE careful with that boiler size, radiation size only matters when trying to determine system operating temps or for steam boiler capacity (and even this isn't always true).

Boilerpro

Unknown

circ pump on gravity system

Before installing a pump by sizing it according to a field formula you to figure out the head pressure the pump has to pump against.

Based on what you describe 1 would use a 1" B&G series 100 or equal pump. This pump will pump about 25 gpm at 8 feet of head. Typically a pump this size has been used in a house your size for more than 80 years.


jake

Mark J Strawcutter

keep in mind

that the reduced piping is very short. It would be very different if you replaced all the 2in with 3/4.

Mark