Balancing radiators in a gravity hot water system

Jerry Boulanger_2

Although it seems backwards, the top floor radiators in a gravity hot water system are actually favored for flow. It was common to install orifice plates in the pipes to the top radiators to force flow through the radiators on the main floor. If the system were converted to forced circulation, the main floor radiators became favored and the orifices had to be moved to the main floor.

Another problem could be the location of the thermostat, typically on the main floor and sometimes in a location where by the time it is satisfied the top floor is toasty.

Jim_78

Balancing radiators in a gravity hot water system

I am getting way too much heat on the second floor of my 1890 home (every room has an equally sized radiator) so I've tried turning the valves on the second floor radiators off to reduce the heat up there. But the radiators still get hot. Do I need new valves or am I missing something?

clammy

gravity

Is this system stilla true gravity with no pumps .Are all the hand valves open on the first floor ? If 1 st floor rads valves are open and second floor closed and still getting hot then it may be time to add a pump to help it along the inside of the pipe is most likely clogged with stuff and is retarding the flow of hot water to the first floor and sending it to the second it may be time to add a pump might be a little to much firction for gravity because of age hope this help s ya .Peace and good luck clammy

R. Kalia_8

If insulation was added to the attic in modern times, this could be the reason why the upstairs is now warmer than downstairs. It isn't surprising that the 115-year-old valves don't close all the way any more; this is a common problem in old houses. But you can't control temperature very well with manual valves, so putting in new manual valves won't help much.

The solution is to put in thermostatic valves (TRVs, such as those made by Danfoss) on the upstairs radiators. At that point you'll have individual temperature control in each upstairs room.

If you add a pump to a gravity system, that also changes the balance, so make sure it is properly balanced...or install TRVs.

Jim_78

Thank you all for the information - I've learned a lot already. I have a few follow-ups:

After closer inspection of the boiler, I discovered what appears to be a new pump in the system - the boiler is fairly new so I guess it makes sense that they would have added a pump. I just got the house so I don't know when either was done. There has also been insulation added to attic, so I am sure that contributes to the problem. And moving the thermostat might help the second floor, but the first floor is comfortable so I'd hate to lose that by moving the thermostat to a warmer location. All of the valves on the first floor are wide open, but I am also noticing that one of the 4 first-floor radiators (the largest) actually doesn't get as hot as the other three on the first floor. So there is definitely an imbalance somewhere.

I am thinking about looking for the orifices Jerry aluded to. Is there any way I could tell without getting into the pipes if the orifices are correctly positioned now, assuming that the system is now forced?

Replacing the valves, as Cricket suggested also seems to make sense (or at least checking out on of them to see if its no longer functioning), but does the entire system need to be drained to do that. I don't see any other valves in the rest of the system (other than the ones at each radiator inlet). If the system has to be drained to check/replace valves, would it make sense for me at that time to have the pipes flushed/cleaned? Is that possible?

Thanks again.

R. Kalia_8

> After

> closer inspection of the boiler, I discovered

> what appears to be a new pump in the system - the


You originally said you had a gravity hot water system. That term applies only to a system where water circulates by convection, without a pump.

> moving

> the thermostat might help the second floor, but

> the first floor is comfortable so I'd hate to

> lose that by moving the thermostat to a warmer location.


Yes, that's not a good idea.

> I am thinking about

> looking for the orifices Jerry aluded to. Is

> there any way I could tell without getting into

> the pipes if the orifices are correctly

> positioned now, assuming that the system is now

> forced?


No, you have to take the valve off the radiator.

> Replacing the valves, as Cricket

> suggested also seems to make sense (or at least

> checking out on of them to see if its no longer


If you close a valve and the radiator still gets hot, by definition the valve is no longer functioning properly. Nothing else to check out; you have to live with them or replace them.

> , but does the entire system need to

> be drained to do that.


Yes, since you don't have any isolation valves.

> would it

> make sense for me at that time to have the pipes

> flushed/cleaned? Is that possible?


Sure. It's not a common request so your contractor may not want to do it. No one can guarantee that it will make a difference, but it's not a bad thing to do.

Mike T., Swampeast MO

IF restrictor plates were used you'll find them at the upper floor radiator union connections--usually but not always on the valve union. Occasionally on the plain angle union. IF you find them, relocate them to lower floor radiators (of course the valves/unions will have to be the same size and lower floor rads--even of the same or smaller size as upper--usually have larger connections on gravity systems). If there's a size mis-match you can make or have made similar restrictors--they're quite simple as you'll see.

I'd lay odds that you won't find the restrictors as they're more likely to cause an under-heating situation of upper rads on a converted gravity system...

Thermostatic Radiator Valves (TRVs) are an EXCEPTIONAL way to balance these old systems once they're driven out of balance by forced flow and/or insulation. They're moderately priced--downright cheap when you consider what they do. At a minimum I'd suggest using them on all of the upper rads--for more control use them on all rads. If used on all you'll likely need some simple piping modifications around the boiler.

With simple tools, simple skills and plenty of muscle you can install TRVs yourself. Unless you study a lot AND have significantly greater skills I would not suggest doing any near-boiler piping modifications yourself.

Such systems MUST be drained (at least below the lowest thing you're working on) to do ANY of these changes!

R. Kalia_8

> IF restrictor plates were used you'll find them

> at the upper floor radiator union

> connections


If someone took a gravity system and converted it to forced circ, wouldn't that person have added/moved restrictors to the DOWNSTAIRS rads (as Jerry Baker says below)? If so, those restrictors can now be removed or changed to ones with bigger openings.

Of course we are assuming that the OP, who wasn't quite clear on what a gravity system is, actually has a converted gravity system (rather than one that was designed for forced circ from the beginning).