2 pipe direct return

JBol

My friend got himself in trouble ripping out his 2” cast boiler mains and replaced with ¾” copper supply/return mains. Now only first radiators get hot on each of two loops. I bled every radiator until I got water and the system runs quiet, convinced theres no air. Closed the balancing valve on the first rad, and second one got hot. Second rad has no balancing valve. Also his headers are bushed down to 3/4” before they bullhead to the two branches.



Here’s all the details I can think of…

Cast iron gas boiler at least 50 years old, 137000 btu input

Two pipe direct return ¾” mains

2 loops split front/back of house, 2 story house

5 radiators on front loop, 6 rads on back loop

no balancing valves upstairs, balancing valves on first floor radiators only

circulator on boiler return pumping away from exp tank

headers bushed down to ¾” before branches split on bullhead tees

lastly, system used to work with 2” mains! Too late to go back.



The fundamental problems I see are lack of balancing valves on a 2 pipe system, and undersized headers. The system could benefit from a boiler bypass as well, no?

Are monoflow tees ever applicable on a 2 pipe system? Any other advice?



Thanks for anyone who can help.

Jesse

JBol

bump

I am doing the above job this weekend. Was hoping for some answers so i can get the right parts and plan accordingly. In need of heating help! Thanks...

Alan (California Radiant) Forbes

If the system worked well before

ripping out the 2" mains will tell you that whatever your friend did was wrong, no?



That 3/4" pipe will eventually ruin the boiler because there's not enough water flow to absorb all the heat being created in the heat exchanger.  Your boiler is probably complaining already.  In addition, 3/4" pipe will only be able to heat maybe a third of the radiators in the house.

Jamie Hall

Sounds almost

as though this may have been a gravity system at one time?  With the big mains?  It may be very difficult indeed to get it so that it's even remotely balanced without going to primary/secondary and zone valves or zoned pumping.  And more flow through the boiler...

JBol

Btus

I would think he could get 80,000 btus out of two 3/4 loops. The boiler can probly only output 100,000 so it's not that far out right? My biggest concern is how will balancing valves affect the btus the loops can draw....

Ironman

Gravity Systems

You might benefit from Dan's article on gravity systems found under the "Systems" tab above:



http://www.heatinghelp.com/article/332/Gravity-Hot-Water-Heating/72/Gravity-Hot-Water-Heating-FAQ