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STEAM HEATING SYSTEMS
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Radiator valve inspection & troubleshooting: here we explain the use, adjustment, diagnosis & repair of hot water or steam heating radiator valves & steam vents to control heat output from individual radiators.
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Guide to Using, Adjusting, Diagnosing & Fixing or Replacing Hot Water or Steam Radiator Control Valves & Vents
Traditional "Manual" Radiator Valves
Radiator valves are opened to allow hot water or steam to enter and heat a radiator, or closed to turn off or reduce heat output from the radiator. By "manual" radiator valve we mean that you have to turn the valve open or shut yourself. We discuss automatic (thermostatically controlled radiator valves and other radiator controls below.
At above left is a top-fed two pipe steam radiator at Google Headquarters in New York City.
This website answers most questions about all types of heating systems and gives important inspection, safety, and repair advice. If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES. If your heating system is not working properly, see NO HEAT - BOILER or NO HEAT - FURNACE.
If your heating system radiators won't get hot, for hot water radiators or convector heat, see COLD HOT WATER BASEBOARD / RADIATOR; for steam heat see COLD STEAM HEAT RADIATORS for help in diagnosing the problem.
If your heat is provided by baseboards there will not normally be individual shutoff valves at those devices, but if your system uses one circulator and provides multiple heating zones (and thermostats) there will be zone control valves (usually near the boiler) that are opened or closed by the room thermostat(s). Cold heating baseboards are discussed at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE.
Which Way to Turn the Radiator Valve
If your heat is provided by individual hot water radiators or convector units, usually there is a control valve at each radiator or convector. Make sure that the control valve at the heating radiator is "open" or "on". Usually turning a radiator valve "clockwise" or "down" closes the valve (turns the heat At COLD HOT WATER BASEBOARD / RADIATOR we include links to additional detailed articles that will help you correct a problem with heating baseboards or radiators that are not working:
Check the radiator control valve: If a radiator is not getting hot: (steam or hot water) first see if the valve that controls it has been turned off. Try turning the valve counter-clockwise to see if it will open.
In our photo (left), the heating convector control valve was found at floor-level under the heating convector. The "open" and "close" directions for this "radiator valve" were nicely marked by the manufacturer (click to enlarge the photo).
If the radiator valve does not turn in that direction, try turning it in the other direction (clockwise or "closed") to see if the radiator valve is stuck. You may also find the same control valve at heating convectors (but not usually at heating baseboards).
While people sometimes turn off radiators in an un-used portion of a building we usually find that most radiator valves have been left in the "on" position - in fact turning off a hot radiator in some building areas could lead to its freezing and cracking.
Steam radiators, on the other hand, can usually be turned-off with impunity since steam radiators do not normally contain water in its liquid form. [That's true at least so long as condensate has not become trapped inside of the steam radiator.]
Watch out: don't use excessive force to try to turn a "stuck" radiator valve. First, you may be trying to open a valve that is already in its fully-open position. Second, the valve may actually be jammed. Excessive force can break the valve or even cause a leak. If the valve won't turn at all counter-clockwise towards "open", try turning it the other way - clockwise, towards "closed". If the valve now turns you'll know it was already in its open position.
Watch out: even if the radiator valve appears to be "open" - that is, turned fully counter-clockwise, if the radiator valve stem is broken internally you may be just turning the knob but the valve may be staying closed inside. If your radiator valve turns too easily or if it does not appear to raise (opening) or lower (closing) when turning, and especially if turning the valve makes no difference in the behavior of the radiator, the valve stem may be broken. (First check for air bound radiators or if your heating system uses steam, check for a steam vent that is not opening.)
Usually while turning a radiator valve to from "closed" to "open" position, if you look closely at the valve stem - the metal rod or shaft extending below the knob you are holding, and extending into the body of the valve itself - you'll see that as you "open" the valve the stem gets "longer" and often a less-oxidized, shiner part of the valve will become exposed as it moves upwards from having been inside the valve body.
That's a great way to convince yourself that yes, the valve is probably opening internally too, you're not just turning the knob. If the valve body has broken loose from the valve stem, that's an internal problem you can't see, but turning the radiator valve knob, even if it rotates, will not open a broken, stuck, frozen valve.
If only some of your hot water radiators, hot water heating convector units, or hot water baseboard heating sections are not getting hot and the radiator valve is open, see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE (hot water heat) or if a steam radiator valve is open but the radiator is still cold, the steam vent may not be working. See RADIATOR STEAM VENTS and also STEAM HEATING SYSTEMS for details.
Hot Water Heat Radiator Valves
In our photo at left you can see not only the radiator control valve, but lots more information:
This radiator is being fed from the top. We know that this must be either a hot water radiator or a two pipe steam heat radiator.
Now look closely at that air bleeder connector on the side of the radiator valve.
From this detail we can conclude that this is a hot water heating system, not a steam heat system
Hot water can enter a hot water (hydronic) heating radiator at the radiator top or bottom. Hot water radiators may have an air bleeder valve but never a steam vent valve.
Steam can enter a steam heating radiator at the radiator top too (most but possibly not all two pipe steam heat systems) or also at the radiator bottom (one pipe steam heat systems).<
Steam Radiator Control Valves
If your heating system uses steam radiators or steam convectors see COLD STEAM HEAT RADIATORS for help in diagnosing and fixing steam radiators that won't get hot. Excerpts from that article are found below.
First check the radiator valve. It's standard to ask first "is the radiator valve turned on or "open" (fully counter-clockwise)?
But other problems can cause a steam heat radiator to stay cold when you want heat.
If a steam radiator valve is open but the radiator is still cold, the steam vent may not be working.
Our photo (above right) shows a typical steam radiator vent.
See STEAM RADIATOR PIPING CONNECTIONS for an explanation of different types of steam piping and steam-radiator piping connections.
On a heating convector unit there is usually an individual valve that lets the unit be turned down or off - but as our photo (left) shows, the valve can be a little harder to spot.
Unlike a radiator valve, a heating convector control valve may be hidden by the convector's steel cover, or it may be little and hard to recognize as we show here.
This valve, if it's not jammed by corrosion, is operated by a screw driver; it may be possible to get this valve working by gently loosening the lock-nut and then turning the control screw with a flat-bladed screwdriver.
Do not take apart this valve while the heating system is on and hot - you risk getting sprayed with hot water or you may start a leak that's hard to stop without making a mess and having to shut down the whole heating system.
Manually Setting the Radiator Valve
On hot water heating systems and two-pipe steam radiator heating systems you can adjust the radiator valve to:
If your hot water radiator is too hot or the room is too hot, you can partially-close the radiator valve.
If your hot water radiator is too cold, be sure that the valve is open and that the radiator is not air bound. Details are at COLD HOT WATER BASEBOARD / RADIATOR
If your steam radiator is too cold be sure that its supply valve is open. If it's a one pipe steam heat system (only one pipe comes to each radiator), be sure that the steam vent is working (you should hear it hissing when steam is rising in the system). Details are at COLD STEAM HEAT RADIATORS.
If you steam radiator is too hot in a two-pipe steam system, according to the U.S. DOE,
If your steam heating system pipes are noisy see BANGING HEATING PIPES RADIATORS wHere we explain steam condensate return problems that can cause banging clanging pipes.
There are additional methods for automatically controlling the heat output from individual heating radiators, for both steam and hot water heat: thermostatically controlled radiator valves and adjustable or thermostatically controlled steam vents. We discuss these controls beginning at Automatic or Thermostatically Controlled Radiator Valves - TRVs.
The radiator control valve opens or shuts to allow hot water or steam to enter and heat the radiator. An automatic or thermostatically controlled radiator valve allows you to set the desired room temperature. The valve will automagically open or close to attempt to control room temperature to the desired level. Keep in mind that with any heat control installed right at the radiator, the control will be sensing temperature in that location, not across the room, so some experimenting to find the best setting will be needed.
Armstrong Corp. provides the RV-4 One-Pipe Steam Radiator Valve that operates as a room thermostat suitable for residential low-pressure steam heating systems. By installing a thermostatically controlled steam vent at each radiator, every radiator can be controlled or set to the desired temperature.
There is a central advantage of thermostatically operated steam vents over swapping out the actual radiator control valve for a thermostatically controlled radiator valve, that is, they are easier and less disruptive to control. The original steam vent is simply unscrewed and the new thermostatically controllable steam vent is screwed in at the same location.
Watch out: it's safer to install or change steam heating system parts when the system is not calling for heat and when the steam boiler and radiators are cold. Don't be fooled. If your heating system is on and the steam boiler is hot, unscrewing the steam vent on a "cold" steam radiator will allow steam to rise into the radiator (forcing air out of the steam vent opening) and you could be seriously burned by rising steam.
Replacing Manual Radiator Valves with Thermostatically Controlled Radiator Valves
If you have to replace the control valve on a hot water or steam radiator or convector unit, consider installing a new valve that incorporates a thermostat as well.
Several companies provide thermostatically-controlled radiator valves including Armstrong, Danfoss, Hoffman Specialty, Jacobus (Maid'O'Mist) and others. The automatic radiator valve shown at left was observed on a typical modern European installation in Molde, Norway.
This (more expensive) radiator control valve lets you treat each individual radiator as a "heating zone".
As long as the room thermostat is calling for heat, each radiator can be regulated automatically when a thermostatic radiator valve (TRV) is installed..
When steam is first rising in a one pipe or two pipe steam heating system, the steam heating radiator will be cool as will be the steam vent. Our photo (left) shows what looks like a Hoffman 1Afloat-type radiator steam vent. This is a residential low-pressure (1.5 psig) steam vent. Similar models include the Hoffman Model 40 (6 psig) and model 70A (11 psig).
Two Pipe Steam Heat
In a two-pipe steam heat system, steam rises through the supply side of the radiator (where the radiator valve is found) and may push air and later condensate out through the return or condensate drain side of the radiator.
One-Pipe Steam Heat
On one-pipe steam heat systems the radiator valve is normally fully open (for the radiator to operate properly) or fully shut (no heat); you may find that some one-pipe steam heating system radiators will not work properly if the valve is left "in between" these positions.
Steam rises and enters each heating radiator through a single pipe, pushing air out of the radiator through its vent. Condensate returns to the boiler through the same pipe, passing out through a special passage in the radiator control valve.
For details about steam heat piping & steam pipe radiator connections & definitions of different types of steam heat see STEAM RADIATOR PIPING CONNECTIONS
Role of the steam vent on one pipe steam heat systems:
Unlike radiator valves that are closed manually or automatically to control the entry of hot water or steam into a heating radiator, steam vents are located at the opposite end of the radiator from the valve and are used to vent air out of a steam radiator so that steam can rise into and heat the unit. When steam reaches and heats the steam vent, the vent is designed to close and stop venting air (or steam), and the radiator will heat.
The steam vent opens, allowing air inside the radiator to be pushed out by rising steam that enters the radiator at the radiator bottom where a radiator valve is present and open.
The "hissing" sound you hear from the steam vent is air being pushed out of the radiator, and is normal. When the steam radiator and steam vent have become warm or hot, the steam vent closes (and is quiet).
Steam vents that won't open properly:
If a steam vent stops working and fails to open, rising steam cannot enter the radiator and it will be slow to heat or may not heat at all. If your one pipe steam radiator won't get hot, the air vent may be clogged or it may just be worn out and need replacement.
Steam vents that won't close properly:
If a steam vent stops working properly and fails to close, the vent will hiss and release steam (and sometimes produce condensate or water) continually all during the heating cycle, wasting heat, increasing heating cost, and in some cases creating a moisture problem or even a burn risk at the radiator.
For details see RADIATOR STEAM VENTS where we discuss other steam vent problems such as spitting water, clogging, etc.
Guide to Choosing & Installing Adjustable or Thermostatically Controlled Steam Vents to Control Steam Heat
Types & Properties of Steam Radiator Vents
Each of these steam vent types is discussed below.
By controlling the rate at which a steam radiator gets hot, adjustable steam vents are a key instrument for balancing steam heat in a building.
Watch out: although adjustable steam vents can control the rate at which a steam radiator gets hot, these adjustable air vents are not identical in function and application nor is heat control using adjustable steam vents identical with that provided using thermostatically controlled radiator valves.
Thermostatically-controlled no-float steam vents
Watch out: Some "thermostatically operated" steam vents include user-adjustable controls that permit the steam vent to operate as an individual room thermostat. But watch out: other "thermostatically operated" steam vents may be units that are not adjustable for controlling room temperature.
These "thermostatically controlled" vents are describing how the vent works internally, not its function as an occupant-adjustable room temperature control.
Hoffman Specialty heating products offers thermostatically operated steam vents (such as the Hoffman Special Steam Vent Model 3 (Part No. 401419) no internal float, image at left) that can automatically regulate heat from individual steam radiators. These vents are used for Air Line or Paul Systems.
The Hoffman Specialty Thermostatic Temperature Regulators (Series 1140 & 1141) are designed for commercial and institutional HVAC systems. These devices permit a set temperature ranging from 40degF. through 220 degF in increments of 40 degF. (no fine tuning).
Watch out: these steam regulators fail "open" (meaning heat fully on), so Hoffman warns that an alarm or cut-off must be installed where overheated water (or steam) could cause harm. Failure to follow this warning could cause serious burns, personal injury, or death.
For more conventional steam vents, take a look at the Hoffman Specialty series 2000 and the Hoffman Model 3 Steam Air Line Valve (Part No. 401419) for an example.
A Hoffman Vent, Model 3, is also thermostatically controlled, operates on temperature only, and does not close against water. Hoffman also produces conventional steam radiator vents such as their traditional Model 1A air valve, and also the Hoffman Model 74 float operated steam unit heater air valve. But these vents do not include a readily-accessible temperature adjustment. For steam heating convectors, different steam vent models are required due to the different operating pressures and vent locations that may be present.
Watch out: when replacing a steam vent be sure that you buy the proper vent for your heating radiator or convector type, or that the steam vent specifications of the new steam vent match the old one. Hoffman and other control manufacturers provide selection guidelines for steam vents as well as their other controls.
Float-type steam vents
As we introduced above, float type steam vents use a water+alcohol-filled float inside the steam vent heats, rises, and closes the vent as the radiator heats. The float also rises to prevent water from spitting out of the vent should condensate rise inside the radiator or vent. Rust or sediment can clog the float vent opening and interfere with its proper operation. Excessive steam pressure can also prevent the vent from operating properly.
Adjustable steam vents
Also as we introduced above, manually adjustable steam vents operate similarly to the float-type steam vents described above, but add the feature of adjustable air vent opening size so that the air venting rate can be better matched to the radiator size. (Larger steam radiators need a larger air vent opening.)
Examples of manually adjustable vent-rate steam vents include: Hoffman Model 1A (Part No. 401422) adjustable air valve with 6 settings (1-slow to 6-fast venting); VariValve® Quick-Vent. Those vents are designed for traditional steam radiators. If your steam heat is by a steam convector unit, different steam vents are required, such as the Hoffman Specialty Model 1B (Part No. 401425). Additional steam vents are listed at references below.
Adjustable Thermostatically-operated steam vents
Thermostatically-operated steam vents (shown here) include an adjustable room temperature thermostat that allows the occupant to set the desired room temperature. Setting this control actually adjusts the rate at which the steam vent permits air to escape from the individual radiator, similar to the adjustable steam vents described above, but in this case once the thermostat is set, the automatically regulating steam vent is responding to the room temperature setting.
Some adjustable automatic air vents for steam radiators include:
Thanks to reader Paul Ruudfor discussing improved steam heat controls and thermostatically operated steam radiator valves and air vents.
Watch out: If the radiator continually makes noises (whistling or wheezing) at the steam vent, there is a problem that needs to be fixed: a bad steam vent, steam piping problem, steam pressure set too high, or boiler oversized for the heating distribution system.
Watch out: to be sure your steam heating system and its controls are properly adjusted excessive steam pressure can be dangerous.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs) about hot water heat radiator valves & steam heat radiator valves
Question: where do steam pipes enter steam radiators: top, bottom, or both?
I had a question about the article at RADIATOR VALVES & HEAT CONTROLS.
I’m looking at the sub-section “Types of Radiator Valves: Hot Water vs. Steam” and here is a copy of the 1st paragraph; the writing becomes nonsensical and near the end and it may turn out that some of the information is incorrect: “In our photo at left you can see not only the radiator control valve, but lots more information: we can conclude that this is a hot water heating system, not a steam heat system because first, the valve is mounted at the top of the radiator (water, not steam - steam enters at a radiator bottom but sometimes so does not water; the reverse is never true).”
I was trying to make sense of what was written and discovered another article (which also has nonsensical syntax- it must be hard to describe these hot water and steam heating systemsJ) which seems to indicate that in fact steam DOES often enter a radiator at the top. At this point I am just lost. We don’t have many residential systems with radiator systems (steam or hot water) so I am trying to edumacate myself but don’t have anything in front of me to compare what I think I understand.
Kind Regards, -Doug
Reply: Up-feed - Down-feed, One-pipe - Two-Pipe Steam Piping & Radiators - What's the Difference?
Doug, the other page (not at InspectApedia) that you gave provides information from Dan Holihan - probably the most-expert fellow alive when it comes to steam heating systems. Dan's text includes these two statements:
Dan is right again. Most two-pipe steam heat systems will show up with the steam entering the radiator at one end at the radiator top (below left), and the condensate return will exit at the bottom of the radiator at its opposite end. 
All one pipe steam radiators are fed with a pipe connection to the bottom of the radiator.
In response to your question we have added an article to help clarify the different types of steam heat piping - to - radiator connections and where valves will occur. Please see STEAM RADIATOR PIPING CONNECTIONS
Questions & answers or comments about using, adjusting, & repairing radiator control valves and vents for both hot water and steam heat systems
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