Half of split hot water zone not as hot as other half

moallen

I have a hot water heating system with 3 zones in an 1800 sq ft raised ranch (2 levels). The boiler is on the 1st level in the garage. The rest of the 1st level is finished with a bath and rec room. I keep the 1st level at 55 degrees. I attached a drawing to show the general layout of the baseboard radiators, including the length of the heating fins.

Zone 3 heats the entire 2nd floor. It is split into 2 loops, which I'm calling 3a and 3b. I can't say that the dining room and living room are noticeably colder than the rest of the 2nd level living space. But when I touch the return pipes at the boiler, the 3b return is too hot to touch, while the 3a return is barely warm at all. All 4 returns have a gate valve and all are wide open.

The bedroom pipes do make minor expansion noises when heating up. However, I never notice that in the living room. I tried bleeding the dining room and living room radiators. Only water came out, no air.

My question is if it is proper to try balancing a split loop zone by partly closing the gate valve on the overly hot return?

moallen

Or on 2nd thought, maybe I have things reversed in my mind. Maybe a cool return pipe means the radiators on that loop are doing a good job of dissipating heat?

If that's the case, what can I do about the other loop returning overly hot water?

Zman

Does each zone have it's own circulator or are there zone valves. In either case what model is it.
One would expect that your zone 3A with bigger pipe, shorter length, and less emitters would return hotter water than 3B.
Balancing the zones with the gate valves is not a very elegant solution but should not hurt anything.

moallen

The oil boiler is a Buderus G115 112,000 BTU. Each of the 3 zones has a circulator. The system doesn't have any zone valves.

In other words Zone 3 has 1 circulator but splits into 2 loops. Each of those 2 loops has a gate valve where they return to the boiler.

The house was built in 1970, but I think everything but the baseboard radiators and the pipes going to them was replaced in 2005.

I guess it's possible the 2nd level was originally just 1 loop or some other arrangement but was split in 2005.

I have a temperature gun and just now decided to take some measurements. Now I'm even more confused.

With nothing going on, burner off and nothing circulating - zone 3, loop "a" return too hot to touch (measured 138 degrees) while loop "b" felt cool (measured 72 degrees).

Ok, turned zone 3 thermostat up to 80. Waited a few minutes to check return temps. Both burner and circulator were on. Zone 3, loop "a" very hot (measured 150 degrees) while loop "b" now measures 118 degrees.

So maybe the temps when running are not that unusual, but why the difference when not running? It's almost as if the boiler is forcing hot water back up that loop return in reverse.

Brewbeer

Can you close the valve on 3a so that all the zone 3 flow goes through 3b ?

moallen

Ok - I just tried closing the valves on 3a and 3b one at a time for about 10 minutes each with the zone 3 thermostat cranked way up.

Which ever return line is open gets up over 140 degrees while the closed loop's return drops down in the 80's.

I guess this means there's nothing basically wrong with either loop. It just means they are not balanced very well.

I would think they should be balanced such that the loop with the bedrooms (3b) would run cooler than the loop with the living room. In my case, it is balanced just the opposite.

I could partly close loop 3b's return valve, but I tried that a couple weeks ago and the bedroom radiators were too noisy. Normally, I have very little expansion noise.

What would be a good way to balance the 2 loops. I don't want to get into major re-plumbing. Could I install an electrically operated valve on the bedroom loop?

Jamie Hall

It is a balancing problem, and what I, at least, would be looking for would be one thing: enough heat from each of the zones to be comfortable. Whatever works.

However, you have a bit of a problem: if those really are gate valves, they were never meant to be used for balancing a system. In principle, a gate valve should be either fully open or fully closed, never in between. You can use them for balancing, but they are pretty crude. Not saying you can't do it -- you can. It may be finicky. Worse, it might be noisy.

Dave H_2

If nothing is wrong and the house is heating just fine, not much to do other than enjoy!
If the expansion noises are getting too much to bear, than you can use an outdoor reset control that doesn't require cutting into the system other than adding electrical.
If wanting to balance the flow and increase the efficiency of the zones to get better delta T's, then balancing valves are needed.

Dave H.