3" CAST IRON PIPES REPLACE WITH COPPER OR PEX?

FeelingColdColdCold

Old house was heated by steam now hot water had furnace replaced but the old 3" cast iron gravity fed pipes left behind. Now plan to replace low hanging big pipes as finishing basement. Differing opinion on using pex or copper (1.5") throughout. Will heating performance be better or same? Anything to worry about? House uses cast iron radiators and will replace with another cast iron atmospheric boiler. Did not want modcon boiler because of maintenance needs. Looking for insight!

mattmia2

Is this steam or hot water? you said steam but your questions are about hot water. you can't do it if it is steam.

FeelingColdColdCold

Hot water

PC7060

Pictures please so we can get a better idea of your configuration. 

PS: Steam to hot water conversions are unusual and often ended with unhappy homeowners. . 

mattmia2

PC7060 said:

Pictures please so we can get a better idea of your configuration. 

PS: Steam to hot water conversions are unusual and often ended with unhappy homeowners. . 

I bet it was never steam and was gravity hot water that now has a newer boiler with a circulator

mattmia2

As far as copper or pex, doesn't really matter as long as it is sized to deliver the needed heat to the emitters.

EBEBRATT-Ed

You could do a manifold system and use all smaller pex. You don't want to run 1 1/2" pex. It would be cheaper than copper

EdTheHeaterMan

If you are deciding on a pipe size, you should understand the principles in this book. https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/technical-brochure/fh-z100b-bg-zoning-made-easy-2.pdf. read pages 3, 4, and 5 at least two times to fully understand how the pipe size matters. How to convert flow rate to BTU capacity, The concept of shared piping, and remember that PEX is not exactly the same interior diameter as copper pipe, so the numbers may be somewhat different.

Gravity flow 3" pipe used slower flow rates, compared to the pipe size of a system on a circulator pump. So smaller pipes will move the same amount of heat as the larger pipes of the gravity flow rate system. Just be sure to select the proper size pipes.

Using a combination of home runs to several remote manifold locations or making home runs to the boiler room may both work just as well, You may find that one may be less work and less costly and easily zoned if that is your ultimate goal for better balancing of the overall building temperature.

Hope this helps.

JohnNY

EdTheHeaterMan said:

If you are deciding on a pipe size, you should understand the principles in this book. https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/technical-brochure/fh-z100b-bg-zoning-made-easy-2.pdf. read pages 3, 4, and 5 at least two times to fully understand how the pipe size matters. How to convert flow rate to BTU capacity, The concept of shared piping, and remember that PEX is not exactly the same interior diameter as copper pipe, so the numbers may be somewhat different.

Gravity flow 3" pipe used slower flow rates, compared to the pipe size of a system on a circulator pump. So smaller pipes will move the same amount of heat as the larger pipes of the gravity flow rate system. Just be sure to select the proper size pipes.

Using a combination of home runs to several remote manifold locations or making home runs to the boiler room may both work just as well, You may find that one may be less work and less costly and easily zoned if that is your ultimate goal for better balancing of the overall building temperature.

Hope this helps.

Such a great book. I hope they still print hard copies. Thanks for posting.

Mad Dog_2

Johnny.  Those old  B&G books are the best.  Dan wrote many of the later (1970s & 1980s) ones, me seems to remember.  I have always revered my elders and played "sponge' with many an old timer.  Because of the great interest I showed, when they finally packed it in or died, I was given all their old 📚 books, sometimes their father & Grandfathers books. Its great perusing them and light bulbs 💡 going off!  Mad Dog 

ethicalpaul

PC7060 said:

Pictures please so we can get a better idea of your configuration. 

PS: Steam to hot water conversions are unusual and often ended with unhappy homeowners. . 

I wouldn't call them unusual. I think every hot water system in every old house in my whole county used to be steam.

george_42

I think you mean 3 inch steel pipe with maybe cast iron fittings

EdTheHeaterMan

ethicalpaul said:

PC7060 said:

Pictures please so we can get a better idea of your configuration. 

PS: Steam to hot water conversions are unusual and often ended with unhappy homeowners. . 

I wouldn't call them unusual. I think every hot water system in every old house in my whole county used to be steam.

Who told you that you were allowed to THINK?