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Old 12-03-2008, 10:21 AM   #1
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No/little heat on 3rd floor apt


I am part of a three unit condo all tied to the same hot water radiator heating system. The 1st and 2nd floor are getting heat just fine but the 3rd floor heat is not coming through unless the temperature is turned up to 77 degrees (which in turn cooks unit 1 and 2). Does this sound simple case of needing to bleed the radiators or something more complex? Any help appreciated.

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Old 12-03-2008, 04:05 PM   #2
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No/little heat on 3rd floor apt


when we get this problem at work, it's because the water pressure in the boiler is low. I'm not the one to say how much pressure you need. Post back how much pressure its reading, and if boiler is running at the time you take the reading, someone will be able to help you.

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Old 12-04-2008, 12:33 AM   #3
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No/little heat on 3rd floor apt


Quote:
Originally Posted by collar View Post
I am part of a three unit condo all tied to the same hot water radiator heating system. The 1st and 2nd floor are getting heat just fine but the 3rd floor heat is not coming through unless the temperature is turned up to 77 degrees (which in turn cooks unit 1 and 2). Does this sound simple case of needing to bleed the radiators or something more complex? Any help appreciated.
Really, the big question here is: Do you have a thermostat in your apartment? If so, then it's a zoned system and it's a completely different can of worms than a system that uses balancing valves. If there is no thermostat in your apartment, then there is also no zone valve on the radiator loop in your apartment, and somewhere on the radiator loop in your apartment will be a "balancing valve". Read on...


The cause can be:

1. As Dude says, the water pressure in the heating system being too low.

Water has a pressure gradient of 0.4333 psi per foot of height. So, guestimate the difference in elevation between the boiler pressure gauge and the top of the radiator in the top floor apartment in feet, multiply by 0.4333 psi per foot and you need to have that pressure, or 12 psig, whichever is higher in your heating system.

You typically need a minimum of 12 psig to ensure there is no cavitation of the impeller in the circulating pump.

As long as you're above that 12 psig, then the pressure has to be high enough to support a column of water as tall as your heating system is, and that's the difference in elevation between the boiler's pressure gauge and the top of your radiators. Any higher pressure than that isn't necessary, but it's safe to operate your heating system anywhere up to about 25 psig. Above that, and you start to run the risk of your pressure relief valve spilling water onto the boiler room floor. It's set to release water pressure at 30 psig to protect the boiler from cracking due to excessive internal pressure.

2. Air trapped in the radiators:

Typically, air in the heating system will migrate to the top floor. You need to bleed this air off. You can have 20 psi showing on your boiler's pressure gauge, but if you have air compressed to 15 psi in the top floor radiator, then no hot water is going to flow through that top floor radiator, and that top floor will be cold.

If you open the top floor radiator air vent(s), and nothing comes out, then your heating system pressure is too low. Basically, what you're dealing with in that case is a column of water that's not tall enough to reach the top floor.

You SHOULD hear a strong blow of air coming out of the air vent until water starts to squirt out of it.

Now, there are two kinds of air vents. "Coin" and "thumbwheel" air vents that are opened and closed manually by turning a screw with a coin or screw driver or by turning a small knob. There are automatic air vents. Look on he wall at the ends of the radiator loop in your apartment, and if you see a panel on the wall, that will likely be where the top of the riser is, and they will typically put an automatic air vent at the top of each riser. (That way, the system bleeds itself off every time you refill it with water after a repair.) The problem is that automatic air vents can be unreliable and can stick open after you drain the water to perform a repair. The result will be that you'll have water coming out of the air vent when you refill the system, with the resulting and predictable plaster or drywall and paint damage to the ceiling below that automatic air vent. If you discover any of these demons, I'd recommend you replace them with a manual air vent.
I've never known an automatic air vent to stick closed, they only stick open in my limited experience.

3. Balancing valve
It won't occur to the average joe, but NO HVAC contractor is going to build a heating system with three radiator loops without providing balancing valves on each loop. Otherwise all the water is going to go through the shortest and/or straightest loop, or typically through the lower floor's radiator loop.

Here's where I fly off on a tangent:
If there is a thermostat in each apartment, that means that each apartment is "zoned". That means that the thermostat on the wall in each apartment doesn't control the boiler. Instead, the boiler has an independant controller, and the thermostat in each apartment only controls a zone valve that diverts hot water flow through each apartment's radiators. In a case like that, there will also be a "wild loop" typically going through the radiators in the front and back entrances where the water flows when all three zone valves are closed.

And, here's where I come back to the situation at hand.
However, if there isn't a thermostat in each apartment, then you need to rely on balancing valves to control the flow through each radiator loop so that each loop offers the same resistance to flow so that water flows in approximately equal amounts in all radiator loops to keep the whole building uniformly warm.

Typically, balancing is done by installing a gate valve on each radiator loop except the longest one, which typically goes to the radiators in the front and back entrances to the building. The gate valve on the shortest and/or straightest loop is pinched off the most, and the gate valve on the second from the longest radiator loop is pinched off the least so that all radiator loops offer the same resistance to flow to the water.

Perhaps you closed a balancing valve? Perhaps the tenants on the first and/or second floor opened their balancing valves? Balancing valves are not meant to be open or closed. They're meant to be left in a partially open position. That's something most homeowners don't know, and will screw up their heating system by opening or closing a balancing valve in the hopes of discovering what it's for.

Try bleeding your radiators. Check your boiler water pressure. Think of any gate valves you've seen on the radiator loop through your apartment and wondered what they were for. Also, the balancing valve for your apartment might not even be in your apartment. If you don't have thermostats in each condo, then look in the condos or the boiler room for gate valves, and MARK THEM AS BALANCING VALVES so that no one monkeys with them once they are properly set.

Hope this helps.

Last edited by Nestor_Kelebay; 12-04-2008 at 12:53 AM.
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Old 12-06-2008, 07:17 AM   #4
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No/little heat on 3rd floor apt


Maybe the two units below are stealing the heat and there is none left for you.

Before you laugh this is a real possibility.

Older structures did this on purpose as the hot air would rise and less heat was needed in the upper floors. Once these places were insulated and sealed then this became a problem.

The situation you describe tells me that it is one circuit and was designed to allow the heat to rise.

There are thermostatically controlled valves that can be put on radiators that will control the heat at every radiator. This is probably the cheapest and easiest way to go.

Also check to see if there are valves on the radiators that can be closed part way in the lower units to restrict flow the therefore restrict heat.
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