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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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11 Answers 11

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
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

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

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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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

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

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

A TEG Peltier hooked up to some small fans may be an option.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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

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

This is an old question, but I just wanted to add:

Adding a fan to a radiator will not increase the 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.

In fact, 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).

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

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