Gravity System and Constant Circ

Dan_15

Thanks for the reply; it looks to me like the system is side-to-side as you described. There are two tees off the main supply going to each opposite side of the house, and then a couple of sub-tees off of those going to a third side of the house. I would have to trace them more closely to figure out where to put ball valves. But Im wondering why that would balancing be necessary in a constant circ environment, where presumably the heat should get pushed around the entire system evenly as a result of constant circ.

Dan_15

I have a 1920 house with an open gravity system that has been modified lots of times over the years. When I got the house the system had been closed and a circulator added (pic attached). After I moved in the water tank busted, so I decided to replace the whole system with a Buderus G215 and indirect tank (pic attached). Last month I finally added constant circ controlled by R2107 with outdoor reset and room sensor. One thing that is a little weird about my new system is that the installer chose to put the circ on the return, probably because that�s where the old circ was connected and he figured not to mess with it.

My problem is that with constant circ I have noticed that the upstairs level is now a bit colder than the downstairs. I have read Dan�s article on gravity systems and I know these can be a little tricky to balance. I studied the mains in my basement looking for valves or anything that could be restricting flow to the upstairs rads, but there are none anywhere. Im wondering if anyone has some insight as to how constant circ should be handled with a gravity system, and what could be going on with mine. Would it make any difference if the circ was moved to the supply? Is the circ sized incorrectly for the head/flow in a gravity system? Its got three speeds�should I turn up the flow? I appreciate any advice you can give. Thanks.

Al Letellier_9

gravity flow

I couldn't see all the connections and existing piping in your photos, but we've done a ton of these conversions with few problems. I doubt moving the circ or changing speeds will help. With old gravity system, head a flow don't factor in as much as with FHW systems. Sure, you need enough head, but the main function of the circ is simply to keep the water moving....slowly...as it did when it was gravity. Most likely your problem is a balancing one. Look closely at the piping arrangement to see how the system is piped. You may not have an easy out, but most systems around here were split, either side to side or floor to floor. A couple of ball valves may be all you need to balance the flow to send a little more flow upstairs.

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

Paul Pollets

Bypass

I'd make sure that you're "pumping away"...it will assure minimal air problems. The boiler also needs to be protected from thermal shock. Use either a full-port bypass on the boiler return or a Thermic valve or a 4 way motorized valve on the supply. Buderus does not warranty their equipment if thermal shock damages the casting. One way to check is to fire the boiler in the morning and time the return temp. (a thermometer should be installed on the return) If the return temp climbs to 130 within 5 min. of boiler demand, you're OK. If not, install the bypass.

We always revalve the radiators with TRV's when the system is drained down . Balancing and efficiency are greatly increased.

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

Dan_15

Thanks, I hear you on that. Im not too much worried about bypass because the G215 has internal design which can handle any return temp. Also it has pump logic set to 104 for condensation protection. I have been a little curious whether I would benefit by moving the circ so that it pumps away, but to be honest I have not experienced any air problems. Ive monitored the rads often and I can say for sure that the system is not air bound and the air separator seems to be doing the trick for now. Im still searching to understand why upstairs would be a bit cooler in a constant circ environment. Maybe the answe is just that I have fewer rads up there than downstairs.

Albany Chris

Some thougts and ideas

With the systems I see, there is no way to balance floors with new central valves, the top and bottom floors often share the same supplys. To balance, I would suggest turning down the valves a bit on all the downstairs radiators to encourage flow upstairs.

Dan wrote that the old men sometimes put bushings in the upstairs radiators to reduce flow since gravity fed flow was higher in the 2nd floor radiators (The opposite of circulator systems). You might want to check the unions of the upstairs valves for these bushings - though I haven't seen them in my old houses.