Gravity Boiler conversion

Jim Eastman

I am considering replacing a 100 year old boiler that drives a gravity flow distribution system that has steel radiators. I have figured the EDR (Thanks, Dan H. for your helpful EDR book)of the rads and have a good handle on the amount of heat I can deliver and the heat loss of the home. I plan to deliver approximately 85,000 btuh. What I have a question about is the size of the circulator for the secondary (radiator distribution system) of my plan. I plan to utilize a Munchkin and a SuperStor with the Vision control. The Munchkin guidelines are specific about the primary circ and the indirect W/htr circ but I am planning on using a Taco 007 for the secondary circ. (after all, this system has been running on gravity/convection for decades!) Is my thinking flawed, or am I on the correct path?

I have done a couple of other conversions with low mass boilers and the 007 works fine.

Anyone have any advice or thoughts to share with me on this plan?

Thanks,
Jim Eastman
Precision Plumbing
Boulder, Co

Boilerpro_3

It pays to wander off the Wall

as Dan puts it. The great Steamhead wrote a very nice pice on this topic that can be found off the wall.

Boilerpro

Wayco Wayne_2

Hey Jim

I've done many gravity conversionsin Washington D.C. where they are many. The secondary circulator doesnt have to be very big if you are keeping the large pipes. The thermosiphon that ran the system all those years was low velocity flow as it was and worked fine. One thing to watch out for is, if the upstairs radiators have a balancing orifice in them. Since hot water rises faster to the highest point in the house there may be an orice in the radiator to slow down the flow so downstairs got its even share of the heat. I usually run the secondary circ at constant flow, initiated by an outdoor sensor (at 68 degrees) or by the B terminal of the thermostat sub base. The B terminal gets 24 volts to it when the homeowner turns the sub base switch to the "heat" position. I run a relay that turns on the secondary circ. WW

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MikeAR

Hey Wayco

Would you have a piping and/or electrical diagram that shows how you did this? I am considering outdoor reset with a condensing boiler for a system like this.

Thanks

Mike

Steamhead

Thanks, BP

I'm glad I could help. Jim, how many square feet of installed radiation do you have? This is a good way to base your circ size, even if there's more radiation than the house needs.

Wander off the Wall to:

http://www.heatinghelp.com/newsletter.cfm?Id=125

for the sizing guide. Note that in a P/S system, the boiler circ and system circ may be sized differently.

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Jim Eastman

Thanks, guys, for the help! Dan's article and your responses confirm what I was thinking. With a modulating boiler and primary/secondary piping, the small circulator should do just fine in my situation. I don't have the figures in front of me, but I think I have approx. 86 sq. ft of EDR in this system. I'll have to check the 007 curve to see what 8.5 gallons at 3.5 ft of head would be.

Thanks a bunch!
Jim Eastman
Precision Plumbing
Boulder, CO

Steamhead

86 square feet

sounds a bit small..... but if you have 86 MBH of radiation (when the boiler is at 180 degrees) on a gravity conversion, try a Taco 005.

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