conversion of gravity water heating to a new boiler

Mike Miller

Using Dan's book on hydronic heating I have been working on a gravity to circulation conversion. I like the two pump system where one return is tied to the opposite supply and the double tees are installed in the other tie in to the boiler. What wasn't clear is if the near boiler piping is still reduced in size as it would be in a single pump system. Anyone's help would be greatly appreciated.

Mike T., Swampeast MO

Yes, you want to reduce the near-boiler piping. The rule-of-thumb is 1/2 of the largest pipe size minus one further size. If largest mains are 2½" that means 1" near boiler. 3" means 1¼" near boiler.

Steamhead (in transit)

And don't oversize your circulator

which is way too easy to do- read this:

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

If you mimic the gentle gravity flow, the system will work great.



To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

You Have a WONDERFUL Opportunity

Not only for exceptional fuel efficiency but for exceptional comfort.

Condensing/modulating boilers generally LOVE these systems as they are so oversized--not only in their radiators, but in their piping. Not only does this usually allow very low system temperatures, but very little force to move the water.

The condensing/modulating boiler will mimic the old coal boiler but you don't have to shovel coal and you don't have to adjust the draft to regulate the fire.

TRVs (thermostatic radiator valves) on EVERY radiator will regulate flow to very closely mimic the original design flow rate. Such is nearly impossible with forced flow because gravity pipe sizing is literally backwards compared to forced flow and the new circulator will usually move water at multiples of the orignal flow.

I honestly can't say which is more important to efficiency: a condensing/modulating boiler or TRVs. This is ESPECIALLY true in the case of a converted gravity system. They work hand-in-hand to produce comfort and efficiency levels that even the designers of condensing/modulating boilers dream about...

One of the MANY benefits of your gravity system WITH TRVs on ALL RADIATORS is that you can EASILY take advantage of the EXTREMELY low resistance to flow allowing ONE TINY CIRCULATOR with the boiler DIRECTLY connected to the radiators. This IS the original design philosophy of your gravity system!!!!

To my knowledge only three condensing/modulating boilers available in the US allow this (direct connection) by their manual. One is the Vitodens by Viessmann. The UB95M by Utica and Prestice by Triangle also allow. Expected flow rates (both minimum and maximum) must however be verified to be within limits and TRVs on ALL radiators will be an absolute requirement. Gravity systems being newly converted to forced flow are almost certain to fall within the acceptable range when TRVs are installed.

Again, you have a WONDERFUL opportunity. Your gravity system was the PINNACLE of efficiency and comfort in its day. Such NEVER came at low cost--it was ALWAYS an investment. After GENERATIONS of service it deserves an APPROPRIATE update!

Mike T., Swampeast MO

Update Bump

nm

Mad Dog_2

Did you pick a boiler yet, Mikie?

Mad Dog

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Weezbo

there are some threads from last year....

on a boiler that was lashed up without a by pass of any sort and was preforming badly mostly the thread gave more than one idea on means of controling the boiler and flow ...let me see if i can find it for you... BRB *~/:)

Try .. Roasting details by jim...

the thread was in November 10 th.

Mike Miller

I have not picked a boiler yet, but in converstions with the homeowner it seems that we will not be getting a condensing/modulating boiler because of cost. So it seems like this will probably be a cast iron boiler. I appreciate all of the help and information. I do need some more help on piping arrangements for this sort of installation. This is in a beautiful older house here in Denver and I would really like to do justice to the dead men who put in the orginal system.