Replacing a Gravity Circulation Boiler

[BronYrAur]

I am in a competitive bidding situation and have been asked to replace a gravity fed (i.e. no pump) boiler. It is an old Utica hot water boiler.

Does anyone make a gravity boiler anymore? Is it recommended? I can add pump if necessary, but again, I'm in a tough competitive market. The boiler serves cast-iron radiators in a 3-story building. I think the boiler use to be coal-fired and has since been converted to natural gas. The burner input was a max of 400,000 BTHU, but I have calculated a building load around 250,000 BTUH.

I was told by a vendor that a Weil-McLain EGH boiler could be used without a pump, but the W-M tech support could not give me a conclusive answer. That particular boiler had only 2" supply and return connections, which seems to be a bottle-neck for natural circulation. The old Utica had two 3" supply and two 3" return connections.

Any thoughts?

 

[RossABQ]

My first inclination would be to no-bid and run as fast as you can!

But seriously, I'm sure someone makes a natural circ boiler. Probably going to be a chore to find it. You may be money ahead adding a pump just to get more bidders. Does the rest of the system appear to have been designed to a uniform pressure rating? What is the Code situation? Is this stamped as a LP HW boiler?

Is there any chance you could bid a retrofit that would have a better energy cost, and justify a higher bid?

 

[ChasBean1]

If Weil-McLain doesn't have the testicular fortitude to help you with how their product can be installed, very simple: do not buy from them. Have you thought about cleaning and re-vamping the existing system?

 

[willard3]

I'm with Chas, thermosyphoning systems last a long, long time if air in the system has been controlled......pressure wash all existing radiator/piping/boiler surfaces and keep what you have.

Thermosyphoning systems will operate when the electricity fails and parasitic losses are very low.....very green.

 

[DrRTU]

The Chicago area has 1000 of these in 3 flats and bungalows. I have seen some hack jobs boiler change outs and magically they work. If the near boiler boiler piping and the mains have not been altered, then you stand a chance on it working. The EG with the heavy CI exchanger is the unit to use. The mfgs. will not give you the time of day due to the liability issues. Run like hell if the owner want to raise the piping in the basement. Did you find the tank and the vents in the attic? I would go with a pump away design and deal with the issue of controlling the flow in oversized piping. This is a code issue. The boiler shall be installed as per mfg's instructions - they do not show an application w/o a pump. Natural circulation in a the boiler will different that a pumped design. Sections of the heat exchanger may not get flow and overheat. The replacement market is dominated by small service companies that will change it out at a very low price. Take a pass.

 

[BronYrAur]

Thank all.

DrRTU, this is a Chicago job. I'm going to quote it the right way with a pump. There is a vented tank up top that I was going to eliminate and use a bladder tank in the basement. I have not been asked to do anything with the piping other than to replace the individual radiator valves with Danfoss valves so that they can have some means of control.