Controlling a hydronic radiator when there is no water shut-off valve.
Hydronic heating means heating with hot water or steam. With older systems it often means overheating as well!
IS THERE NOTHING YOU CAN DO?
Hydronic heating was what kept houses hot a long time ago, and some of the oldest radiator systems are still working today, with new boilers, of course. However, as many homeowners and even more apartment or condo owners have found out, some of these radiators are either too cold, or often too hot, leading to opening the windows in the dead of winter just to cool down the house. Now, that’s energy efficiency at its worst! You ask the building manager how to cool them down, and they say there is nothing to be done.
Well – Yes and No! It is true you can’t change the temperature coming out of the boiler, that is set for the whole building, not just one room. But it is not true that you cannot adjust the amount of that heat that gets into each room of your apartment or house.
TEMPERATURE CONTROL WITH WATER VALVES
On some of the old hydronic systems, and all new hydronic systems, it is possible to install water shut-down valves, manual or electronic thermostatic controlled, at each radiator. But there again, in some buildings where valves could be used, no one invested in the necessary valves. I explain further below about the one type of system that cannot use water valves, and the two systems that can.
CAN’T STOP THE WATER – THEN SLOW DOWN THE AIR
But what to do quickly and easily to cool down the apartment if there is no valve, or you have a series system that cannot use control valves? We can’t change the temperature of the radiator, but we can change the room airflow over the radiator that transfers that heat to the room.
If we block the intake of air at the bottom of the radiator at the floor, the radiator, even its metal cage will get hotter. This is not a fire hazard because it cannot get hotter than the water, never hotter than the hot water pipe feeding the radiator. (If you block the air on a baseboard electric heater, that can be a fire hazard.) So the hydronic radiator still heats the room, but not at all as efficiently as when the air flows freely through the radiator. This is probably enough of a reduction in heat transfer to get below the “overheating” problem. If you need more heat, simply partially remove your air blocking.
The block would ideally be made out of sheet metal, but wood, even cardboard could do as it doesn’t get hot enough to ignite combustible material. You don’t want to use plastic, or rubber like foam or synthethic cousins as these could melt, although not burn. If you can find narrow metal grills that can be partially or fully closed, like those used for forced air floor heating grills, you will have an easily adjustable damper for manual control of airflow for room temperature control. A sliding baffel, like that on your fireplace air intake could work as well.
For a permanent air flow control installation, you could build a full “closet” over the entire radiator. The same hot water pipes are already closed-in inside the floor; it is not a fire problem to close them in a closet-like structure. If you wanted some heat but more control, put adjustable grills in both the bottom and the top of your structure.
Want to see if it works? Simply place a piece of cardboard over the air intake at the floor, as indicated in the photo, and brace it in place with a non-plastic flowerpot. That will tell you if this is worth doing in your house or not. If it works for you, you can do a more aesthetic job, or even convince your condo management that there is something they could do to each overheated room – something that will save them significant heating dollars as people will stop opening the windows in winter.
HYDRONIC HEATING SYSTEMS
Why are many hydronic radiator systems so hard to control?
Let's look at the three ways to connect the radiators to the pipes connected to the boiler. This might help you to identify which type of system you have, particularly if you have an open basement ceiling where all the pipes are visible.
THE SERIES LOOP SYSTEM
As you can see in the graphic, the hot water comes from the boiler, runs through the first radiator, then over and through the second radiator all around the house until it gets back to the boiler. This is called a Series Loop connection. Click on the graphic to see it larger.
The primary problem with this system is that the first radiator will be hot, the second is receiving cooled water so it will not be as hot, and by the time you get to the last radiator, there is not much heat available at all.
Try to insert a shut-down or control valve in the line, and everything stops. Actually, this series system is the same as very old Christmas tree light strings, where when one bulb burned out, they all shut down because the electricity was going through each bulb to the next.
For those stuck with a single pipe series arrangement, the only thing you can do to individual rooms is to control the airflow over the radiators in the rooms that are too hot, as I described above. Actually, this will help the other radiators because more of the heat from the boiler will reach further around the loop than before as the first radiators won’t steal it all.
With time, both Christmas trees light strings and hydronic heating shifted to what we call a Parallel system.
1 PIPE AND 2 PIPE PARALLEL SYSTEMS
All parallel systems can have manual or thermostatic controlled water flow valves at each radiator, although many older installations were never equipped with individual water valves to save money. We didn’t pay much attention to heating costs in those days.
One-pipe-parallel-systems were a brilliant evolution from the series loop for sharing heat more evenly around the house: Run one hot water pipe all around the house and keep the hot water running to all of the radiators. Then tap into that for each radiator and bring the cooler water from the other side back to the flowing hot water line. This still had the effect of losing temperature in the water as it flowed around the house, but the difference between the first radiator and the last radiator were not as bad. It also provided the opportunity to take more or less water for each radiator with individual water control valves, depending on the heating needs of each room – (north side of the house, south side, large, small). With the control valves, the overheating problem was solved and more heat got to the last radiators.
Two-pipe-parallel-systems were significantly more expensive to install because you had two large pipes to install, but significantly more efficient at distributing the boiler’s heat around the house. One pipe ran hot water all around the house like in the other system, but the exit from the other side of each radiator returned to a return pipe which also went aroung the house and back to the boiler. So we still have the same flow of water out of the boiler as back into the boiler, but this time each radiator receives close to the same temperature water. Add thermostatic controlled water flow solenoid valves and each room gets heated to your selected temperature, even more efficiently than a forced air furnace.
AIR FLOW CONTROL COULD STOP OVERHEATING WHEN YOU DON’T HAVE WATER FLOW CONTROL.
Overheating in a large apartment complex is a serious waste of energy dollars, especially if half the apartments have to open their windows in the winter to cool off. Air flow through-the-radiator control could be a profitable solution for the building owner who either has a system that cannot use water control valves, or they don’t want to pay the bill to install such valves. Take that up at the next condo meeting. In the meantime, block the air intake in rooms that are overheated rather than opening the window.