Adding zones to two-pipe heat

tdierks

We own a 20' wide 4-story row house in Brooklyn, NY, with two units: a rental on the ground floor and we live in three floors above. We have two-pipe hot water heat. For some reason I don't understand, when we renovated, our plumbers or contractor never asked us how many zones we wanted, and we didn't apparently take the care to instruct them, so we have one zone for both units, with the thermostat in the hall of the third floor. (There is also some radiant heat on zones of its own, but it's not through much of the house, so I don't think it bears on this question.)

The problem is that our top-floor bedroom is cold. It has two radiators that are on the same main loop as two radiators on the floor below and one or two radiators in the rental. I've bled the radiators, so it's not air lock. After reading Dan Holohan's Classic Hydronics (which referred me here), my best guess is that we need to have some restriction on the lower radiators to force hot water to flow through the top and most distant radiators.

So now what? There are ball valves on both sides of the lower radiators; will partially closing them do the trick? Or do I need to get someone out here? Despite using a multi-generation family plumber here in Brooklyn for the buildout, we've been unable to get them to solve this, so I may need to find someone new.

It's possible that part of our problem is having one zone and that it's not practical to get the whole house to the same temperature without having parts of it be too warm and parts too cold. I'd really prefer to not have to run a lot more pipes through the house to add zones. Does anyone make an alternative solution? To my naive thinking, it seems like it would be possible for someone to make small, quiet circulators that could be placed within the house to control the flow of hot water to smaller branches of radiators, even individual rooms. Or is that crazy talk?

Thanks,
- Tim

nicholas bonham-carter

If the system has been properly installed and configured, I would think that the water temperature reaching all radiators should be identical. If there is any restriction, it could be air in a pipe, rather than a radiator, alternatively, the radiators in the cold room could be undersized. Possibly, the pressure is too low for your 4 floors, and therefore unable to squeeze all the air out of the top rads.
Maybe the valves on the radiators could be adjusted for balance, (ball valves are not good for fine adjustment of flow).
When all the water is flowing properly, then the radiators can be individually controlled with thermostatic valves. The system could then be controlled by some sort of outdoor reset, which will vary the water temperature in relation to the outside temperature. Systems controlled this way burn less fuel, but are not adaptable to temperature setbacks.
Generally these systems should be installed by an expert in Hydronics, rather than a plumber who may only know how to connect pipes together for water supply, and discharge. Use the find a contractor feature here to find someone to fix this problem.--NBC

SWEI

Several options are possible -- thermostatic radiator valves come to mind, but they are not compatible with some layouts. Do you have a piping diagram you could post, or at least a sketch?

icesailor

How much pressure is in the system?

What temperature are you running it at?

tdierks

Thanks, all.

I do not have a system diagram with the rest of the documents for the system, nor do we ever recall seeing one. I can try to hit the installer up for one if they kept it, but I'm skeptical. My suspicion is that they laid it out in a fashion that was standard for them for similar systems, so it didn't require writing down.

I've attached the best diagram I can pull together based on observation.

It looks like there's about 20 PSI in the system, according to the gauge on the boiler. Now I notice that the gauge is also calibrated in feet of water, and that 20 PSI is about 50 feet. 50 feet is also a rough estimate of the vertical distance from the boiler to the top radiator. Does this mean I don't have enough pressure in the system? Opening the bleed valve on a top floor radiator will release water.

If I wanted to add pressure, should I do it by pumping up the expansion tank via the Schrader valve, or by adding water to the system? What's a good target?

I cannot find any way to set the operating temperature for the boiler; it just says "Max 250°". In heating weather, it seems to idle at about 120°, and can drive the house temperature at the thermostat from ~70° to ~75° by the time it gets the boiler temp to 170° (I decided against exploring the top temperature by overheating the house, if only due to familial feedback).

While I titled the post as a question re: zones, I don't have any reason to go that way if I can get the house & rental to a uniform comfortable temperature.

Thanks again for your help & opinions.

nicholas bonham-carter

why not show them your diagram and see if they remember the layout as being like that?
post a picture of your boiler, and piping, and maybe there will be something to see.--NBC

SWEI

tdierks said:

It looks like there's about 20 PSI in the system, according to the gauge on the boiler. Now I notice that the gauge is also calibrated in feet of water, and that 20 PSI is about 50 feet. 50 feet is also a rough estimate of the vertical distance from the boiler to the top radiator. Does this mean I don't have enough pressure in the system? Opening the bleed valve on a top floor radiator will release water.

50 feet of head is 21.7 PSI. If there's really 50 feet between the boiler and the high point, you want about 26-27 PSI in that system.

If I wanted to add pressure, should I do it by pumping up the expansion tank via the Schrader valve, or by adding water to the system?

Both, actually. First you need to isolate and drain the expansion tank. Hopefully there is a valve installed for this, but if not, you will need to isolate what you can and drain the rest. Think about adding a valve with a drain to facilitate this process, because it needs to be done every year or two anyway. Check the air pressure in the Schrader valve and fill the tank to 26-27 PSI.

Once that is done, you can use the autofill (if there is one) or a garden hose to add water until the pressure gauge comes up to the same pressure you put in the tank. You'll probably have to add water more than once as the air makes its way out of the system.

icesailor

IMO, if you open the vent on the top (fourth) floor, and water squirts out of the vent, you have sufficient pressure. Higher would be better, That said, I was taught to never trust a pressure gauge on a boiler. I always carried a quality 60# gauge with a big needle circumference and connected with a double hose washing machine connector. I could connect it to any boiler drain on the system, around the boiler and get a read.

SWEI

Depending on the pump, the positive pressure he is seeing at the top may or may not be there when the system is off.

I would check the expansion tank regardless. An unfortunate majority come out of the box and into systems unexamined.

icesailor

Doesn't everyone carry a tire pressure gauge in their trucks to check for proper tire pressure?

Just perfect fore checking pre-charge in Extrol type bladder tanks.