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I lived all my life with forced air heating and cooling, but my house now has steam radiators. They perform ok, I suppose, but I know from trying that just letting the convection cause the airflow leaves them very inefficient.

With a small 6 inch fan blowing at low speed on a radiator, the room temperature will go up 5-10 degrees F.

I would prefer not to have to run power and fans to every rad in the house. I was wondering what the options were for fans to improve the radiators performance.

Standard round fans are the wrong shape, and only target a small portion of the radiator surface.

I would love something that could draw power from the heat difference, since all it needs is low speed fans to move air better than convection does.

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13 Answers 13

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An alternative that might work in some rooms is a ceiling fan that has a low speed (we have some 6-speed models in our home where the lowest speed just circulates the air slightly). This would help move air around in the room (and thereby helping to move some heat away from the radiators) and has the added plus that you can use it on higher speeds for summer cooling.

We have forced hot air heat, and our master and living room have high ceilings, so we run the fans year-round.

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  • All the bed rooms have ceiling fans, 3 speeds, and the slowest speed is not too bad, but the downstairs (Working from home today) has no fans. – geoffc Jan 5 '12 at 3:17
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    ceiling fans are a great option. You can reverse them each season and definitely help even out the temp in a home. – DA01 Jun 24 '13 at 0:10
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From what I've read and experienced with household radiators: Building a cover over a radiator, according to everything I can find about radiator efficiency, will absolutely decrease efficiency about 30%. This is true even if reflective material is added. Radiator shelves and enclosures were often meant for this purpose - to control an oversized radiator.
A radiator is most efficient when air can flow through it unobstructed, and even more so when the air that flows through it is the coldest in the space. That is why radiators are ideally placed near entrances and windows.

Fans are the answer for increased efficiency and a simple box fan can make a HUGE difference in room temperature. I find that blowing the fan into the radiator, such that air also makes contact with the wall behind, is more effective that sucking air through it. Adding box fans to my current house radiators last winter literally cut my heating bill in half, and kept my house evenly warm.

I am also looking for a quieter solution including 400mm computer cooling fans. Would love to hear ideas from others.

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  • Yup that's what I use. Just had my 10+ year old box fan go out... I was using it to suck in the warm air from the radiator and blow it into the room. Probably that's what did mine in (that and all the grime and dirt... probably should have cleaned it). +1 for the computer fans... might try rigging something up one of these days since I seem to have so many spares lying around... if so I'll be back! – Kasapo Jan 25 '18 at 6:13
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This is an old question, but I just wanted to add:

Adding a fan to a radiator will not increase the overall efficiency of your heating system (at least the way efficiency is normally expressed: usable heat output per unit of fuel, or per dollar). Adding a fan will make the radiator deliver heat to the room more rapidly, but the boiler will then have to work harder to reheat the extra steam that was condensed in the process (and/or the next room in the circuit will not receive as much heat). Once the boiler has heated the water, it's a zero-sum game: the heat is delivered to the various rooms in the house and then whatever heat is left remains in the pipes, lessening the burden for the boiler to reheat the water.

This isn't to say that adding a fan won't increase the amount of heat energy taken from the boiler system by that specific radiator over time, so if you have a cold room, it would work well. A radiator is simply a fluid to air heat exchanger, The addition of a fan will increase the normal convection properties of the radiator and transfer more heat per unit time, heating the room faster, but the boiler system would still have to produce any additional heat used by that radiator at it's normal operating efficiency.

Another factor to consider is that by heating the room to a higher temperature, you will be losing more heat through the exterior walls, perhaps lowering the overall efficiency.

I think it's helpful to think about heating as replacing the energy lost through the building envelope. The only ways to change the efficiency of the system are:

  • add insulation to the house (i.e. reduce the amount of heat lost through the building envelope)
  • get a more efficient boiler / furnace (i.e. reduce the amount of heat lost through exhaust or unburned fuel).

In conclusion, there may be other good reasons to add a fan (such as for that room is colder than others, or maybe the distribution of heat is not even or comfortable), but don't think you're getting free heat out of it.

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There is a pretty new product in the UK market at least, which is a radiator fan unit. It does need a power source but it has a built in thermostat so it only turns on when the radiator gets hot. Seems to be quite effective, we have one and it made a real difference to our living room. Not sure if they are in any stores or anything yet but we just got ours direct from their website. It's called a RadFan. Basically blows the warm air from the radiators into the middle of the room instead of going up to the ceiling or out of the window.

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The best thing you could do is build a radiator cover (see the following This Old House article How To Build A Radiator Cover). The key component to the cover is the reflective material used behind the radiator which reflects the heat back into the room as opposed to being absorbed by the wall as waste. You could, of course, just fabricate a simple backing to the radiator as opposed to creating the entire cover.

A second option is to tile the wall behind the radiator as opposed to placing a metallic material behind the radiator. This might look better than a metallic material in some rooms such as a bathroom.

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  • Thanks Evan. Already have the reflective material behind all of them. I still think increasing air flow is the key. – geoffc Jun 24 '13 at 0:43
  • in that case, have you thought about utilizing computer case fans? the largest "standard" size is 120mm still i believe, which is just shy of 5 inches. – Evan Jun 24 '13 at 1:04
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I saw some small heat-powered fans for wood stoves in a Lehman's catalog a few years ago. I'm not sure if a radiator would put out enough heat to spin one.

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  • Found the Lehmans reference and they have big wood stove ones for $100 and up which is more than I wanted to spend. You would think this would be a more common request? – geoffc Jan 5 '12 at 0:11
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you could make a sterling engine that powers a little crossflow fan and a shroud that guides the airflow

but sterling engines don't start easily, powering the fan (or starting the sterling) from the flow in the pipe might be more reliable

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Not sure how active this thread is anymore but throwing in my two cents on this: I use window fans that i put in the attic windows during the summer. They the the twin fan type with thermostat, have in, out and exchange settings as well as three speeds. When stood on end and placed at the end of a radiator they are barely noticeable, and fully automatic. Just turn it on and rotate the thermostat back until the fan stops when the heat is off. For $40 a cheap and easy fix and works great.

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  • Not a bad idea. I think I actually have one of those too. – geoffc Dec 19 '14 at 3:34
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Yes: http://radiatorlabs.com/ I saw a demo last year. It claims to reduce heat usage by 40%, but only vs an open window...

It is a large blanket with a wireless controlled fan and temperature sensor connected to the furnace. If the room is too hot, it shuts off the fan.

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  • Neato! Alas my rads are embedded in the wall, no room to install these, but I like the idea. – geoffc Dec 19 '14 at 3:34
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A TEG Peltier hooked up to some small fans may be an option.

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  • Karl, welcome to the site. Your answer has a lot of potential, but it's a little short on details. Do you think you provide an expanded explanation of how to implement your idea? – Doresoom Dec 22 '14 at 16:50
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There was research done at the University of Illinois around 1910 or 1920, which showed that the design of the enclosure can shift the radiator's thermal output from -10% to +20, by increasing the convection (air flow) around the radiator, which is the primary mode of heat transfer. Basically, to increase output, you want to have the cover vented along the top, and to allow air input at the bottom. If you have a totally sealed enclosure (excluding the back next to the wall, which is difficult/impossible to enclose), you reduce convection.

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  • As an aside, this is exactly how baseboard radiators are designed. The vent is at the top, opening at the bottom, to get air to circulate naturally via rising. – DA01 Jan 30 '15 at 22:06
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I have heard about the idea that using fans make a boiler work harder, and based on my experience it is a myth...or mistake.

For background, I build kilns and heat treatment furnaces, so the idea that pulling more heat from a radiator, which is a heat transfer device, does not add up. And here is why:

If you have a burner in a boiler setup, that burner will be defined by its ability to deliver fuel that is being combusted to the combustion chamber. We assume the burner is tuned as best as possible with oxygen for as efficient combustionas possible. That burner can only, and will only deliver a flame with a set peak number of BTUs ever. If the burner is 100,000 BTUs then that is what it delivers during each firing period and remains until the home is heated to the target temperature set by the controller and measures by a thermocouple or temperature reading device. Once the set point is reached the furnace is shut off. It fires again when the home temperature drops below the set-point on the thermostat.

The burner in this case is heating a chamber that exhausts to a chimney flue and the job of the heat exchanger is to grab as much of those BTUs as possible before they exit the flue. Any heat exiting the chimney is heat lost.

But the next wrinkle is that the medium in a radiator is generally water or steam. Older boilers run by convection. This concept means hot water or steam will rise and go to cold, creating a flow from hot lines to cooling water exiting radiators and dropping back via return lines to flow into the heat exchanger. This is done via convection and by way of pumps, too.

The medium for the heat carries the heat. If you can grab that heat, it means cooler return lines but the furnace does not sense or feel or work harder due to more heat being drawn out of the loop. It's a 100,000 But burner that burns at 100,000 BTUs no more or less (given its well tuned).

The more heat you grab, the less heat that is lost up the chimney. You have effectively transferred more of your heat from the combustion chamber if you do this.

It is worth noting that some furnaces are so efficient they require plastic pipes to vent the stack gas because so much heat is removed from the exhaust that all that is left is steam. Anything less than a PVC pipe invites corrosion because the exhaust is mostly condensing luke warm steam. And that, my friends, is what you want! You want an exhaust venting a tiny fraction of the heat put out by your burner.

That's my educated opinion, which is: crank up the fans. My own radiators thank you...

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  • This isn't true for a steam boiler. The water is at a constant 212F while boiling; if your radiation is less than input, then steam pressure rises until the pressuretrol shuts the burner down.. if it is greater, then steam pressure remains low as the steam is condensed as fast as it is supplied. In either case the water in the boiler remains at constant temperature. – apraetor Feb 7 '18 at 8:58
  • Also, you mention high-efficiency condensing boilers which produce hot water (they only exist for hot water). Those work by varying the burner rate, actually. They match their output precisely to the radiant load, such that the combustion gases are cooled below 212F, condensing most of the water produced by combustion. Recovering that latent heat greatly improved their efficiency. – apraetor Feb 7 '18 at 9:02
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The fans cannot increase BTU output of the boiler but they can increase overall performance. The exact same way if your radiator fans die in your car you do not want to sit in traffic, @65mph it doesn't matter if they work or not.

The faster you heat the room and satisfy the thermostat the faster the boiler will shut off. The fans can help in situations where you want to redirect airflow due to covers/ furniture.. ect.

I have had my 1920's home re insulated and the windows have been removed and the pockets re framed to accept new construction windows. So I'm fairly well insulated and certainly much more air tight than when I bought it.

What this leaves me with is a lot more heating power out of the radiators than I actually need. Hell they oversized these things to begin with.

I want to strip the heat off that radiator as fast as I can. Simple testing has shown me 2 things. First the room absolutely heats up faster. 2nd its shutting my boiler off faster as well.

So for me doing so will allow me to build the cover in a manner that I find pleasing. It will improve the Hot/Cold spots in my large living room, the bedrooms dont really have that issue. Cost will be reduced in having more boiler down time. My domestic hot water is not run off the boiler I have that on a tankless condensing wall unit.

Another manner this will help is at night. Now the system is about as balanced as its going to get. I have a very large amount of glass on the first floor. During the daytime even when its cloudy I get enough solar heat that its well balanced. Nighttime I can see the 1st floor get much colder. Enough that I either bake upstairs or freeze downstairs.

So for me I will be adding a method to control the fans at night. By retaining the heat withing the covers and keeping them as hot as I can It will cause the vents to remain closed longer. This will cause pressure to build faster causing the pressuretrol to shut down the boiler faster at night. I will have to watch for short cycling but I can adjust as needed.

Here is how I'm going to do it.

I can feed the Thermostat into a 6 zone relay typically used for hot water systems.

This will control and supply power to each fan on the first floor. It will also activate a second relay unit that will power the fans on the second floor. The second unit will be controlled by a timer so they may be disabled at night.

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