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Need info on black pipe installation for a new twin boiler install

in Gas Heating
Hello: To summarize my situation, I'm plumbing my heating system with twin conventional high-mass boilers. The system is a converted gravity system and I'm using information aquired from Dan Holohan's book "Primary and Secondary Pumping made Easy". Mr. Holohan's book's by the way, have been a excellent resource for me... The system uses the system of splitting the heat load between two boilers to save on fuel consumption. My approximate heat load is 120k Btu, based upon my (Minnesota) design temperature of -20 below. At that time of the year, say between January and February; both boilers will be operating, and typically that is the only time of the heating season both boilers will be needed for the load: for the remainder of the season one boiler will suffice.
I'm a machinist by trade, I'm not a professional, thats why I'm seeking your advice. For app. 40 years now I've built and maintained my hydronic systems myself using your help... Most of my past experience has been with sweating copper pipe and fittings for the install. This time I want to use black pipe and forged fittings for the project, because of it's ruggedness and ease of changeover for future modifications and repairs. I just think it looks more professional, it's rugged, and directly compatible with my exsisting 111 year old black pipes and fittings. I have all the tools neccessary, but lack some of the neccessary knowledge for the project. I know how how to thread pipe and (of course) how to use pipe wrenches, but I need advice on proper placement of unions. I need to know of a good supplier of 150lb forged fittings, and I would't object to buying some NOS pipe fittings if anyone has them for sale via mail. Your future help will be greatly appreciated.
Thankyou,
Dale Wilson
I'm a machinist by trade, I'm not a professional, thats why I'm seeking your advice. For app. 40 years now I've built and maintained my hydronic systems myself using your help... Most of my past experience has been with sweating copper pipe and fittings for the install. This time I want to use black pipe and forged fittings for the project, because of it's ruggedness and ease of changeover for future modifications and repairs. I just think it looks more professional, it's rugged, and directly compatible with my exsisting 111 year old black pipes and fittings. I have all the tools neccessary, but lack some of the neccessary knowledge for the project. I know how how to thread pipe and (of course) how to use pipe wrenches, but I need advice on proper placement of unions. I need to know of a good supplier of 150lb forged fittings, and I would't object to buying some NOS pipe fittings if anyone has them for sale via mail. Your future help will be greatly appreciated.
Thankyou,
Dale Wilson
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Comments
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Personally for water I would use sweat copper but black fittings are fine. Your old system probably has cast iron fittings and malleable iron fittings are also acceptable. Any reputable P & H supply house in your area should have the right fittings. Personally I would stay away from the big box stores and Chinease fittings and look for Ward or Anvil brand fittings
So if you know how to thread and use wrenches what information are you looking for? Seems to me you need a piping diagram
Having never installed two boilers on one system before, I can only tell you the small amount of information I've gleaned over the years and perhaps others with more experience will chime in where I've fallen short.
Ideally, you turn on one boiler on a call for heat and if that boiler can't reach setpoint, the other boiler is fired. A 2-stage thermostat can do this by sensing the time it takes the air temperature to respond to a call for heat. Alternatively, a lead-lag boiler control can do this by monitoring the return water temperature. The benefit of a lead-lag control is that it will alternate boilers to reduce wear.
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https://www.caleffi.com/usa/en-us/technical-magazine
Go with what you know!
Lead-Lag is a good idea, but you can set up analog aquastats to keep it simple. If you add a quick connect (extension cord male and female) to the burner control... you can just switch plugs each year to make boiler B the lead boiler in odd years and boiler A in even years.
You got This!
Retired HVAC Contractor from So. Jersey Shore.
Cleaned & services first oil heating system at age 16
Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air
If you make an expensive repair and the same problem happens, What will you check next?
Thanks, Dale
You can make your own lead lag system with 2 aquastats, two spdt switches and 2 relays. I will make a diagram and post it
I posted the lead lag drawing in another thread "cheap lead lag system" if your interested
Dale