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We study modern convectors and deal with fire safety issues

02.01.2024 07:50

Convectors, especially their heating elements, still cause controversy about safety on the Internet. Some people believe that monolithic heaters such as hedgehog are safer and more effective than stitch type heaters. However, many bloggers are spreading false claims, which is confusing.

For example, statements about «intermediate heat loss» are meaningless since the electrical energy consumed by the appliance is converted into heat. Also, statements that the air “does not have time to heat up due to the small heater area” are confusing. Energy consumption here is always proportional to heat transfer, and efficiency depends on the design of the heater, and not on the air.

An exposed heating element does not «burn oxygen» as some claim, because something needs to be oxidized to burn, and the wire itself does not burn that way.

To understand the actual efficiency and safety of the heaters, experiments were conducted with two models — one with a wire «stitch» element, the other with a monolithic hedgehog. The measurement results of the study will help to understand how justified this debate is and what is really important when choosing a convector.

Test instruments

We carried out our tests on two heaters with a declared power of 1500 W.

The first of them is the more modern electric Electrolux ECH-A-1500 M.

It is equipped with a hedgehog type heating element.

The heating element inside such a heating element is located in the central axis, and the heat is distributed through X-shaped “blades” with many “spines”, which makes it look like a “hedgehog”.

Manufacturers and sellers claim that such heating elements have a significantly lower temperature compared to “stitch” heating elements. This means that the likelihood of the characteristic smell of burning dust is reduced, and the possibility of foreign objects igniting inside the device is also reduced.

The second option is the classic convector Resanta OK-1500SN.

It has a stich type wire heating element.

The “stitch” element is a set of zigzag “stitches” made of metal thread. The principle of operation is simple: an electric current is passed through the thread, it quickly heats up and transfers heat to the environment. The metal thread has a low heat capacity, so heating occurs quickly in a matter of minutes, and also cools quickly. This may increase the temperature of the heating element and therefore increase the risk of fire in surrounding areas.

Before testing, we set the heating power to maximum and waited for both heaters to fully warm up to standby mode.

We started testing by checking the heaters as standard: we took the device “as is,” heated it to maximum temperature and tried to set something on fire with its help.

Paper napkins

For the experiment, we took three paper napkins: dry, soaked in white spirit solvent, and soaked in alcohol.

We placed all three napkins in the hottest part of the convectors — where warm air exits. We measured the initial temperature at the air outlet grille. In both heaters it turned out to be approximately the same: from 100 to 115 °C.

It is known that the burning temperature of paper is usually around 451 degrees Fahrenheit, which is approximately equal to 232 degrees Celsius. This is confirmed by various sources, including the reference book “Fire and Explosion Hazard of Substances and Materials and Extinguishing Means” by Korolchenko A. Ya. and Korolchenko D. A. (2004).

Having stocked up with a bucket of water just in case, we noted the time and began to wait, preparing to test the heaters.

There is every reason to assume that the paper will not ignite, especially considering that modern convectors are equipped with a thermal fuse. This means that even if the heater is completely covered with thick fabric, we will not see high air temperatures.

For example, in the Electrolux heater we found a KSD301 thermal fuse that can turn off the device if it overheats when the temperature reaches 110 degrees. This is significantly lower than the ignition temperature of paper, which is about 232 degrees Celsius.

The cost of such a part is less than one hundred rubles at retail. If your heater is not equipped with overheat protection, this may be a concern. This indicates possible savings for the manufacturer, even on such minor details. This makes you wonder about the quality of other components in the device.

After an hour of waiting, we discovered that the alcohol and solvent had quickly evaporated, after which the wipes began to slowly heat up.

However, visually the napkins remained unchanged. There were no yellow stains or other signs of a possible fire.

This leads to the conclusion that it will not be so easy to set something on fire using a working convector without placing the objects inside the device. Especially if the device automatically turns off when the temperature reaches 110 degrees Celsius (such heating is possible, for example, if the convector is completely covered with thick fabric).

We move on to the next stage of testing: we plan to disassemble our heaters and try to place something directly on the heating element.

Combustion on the surface of the heating element

So, after checking the assembled state, both of our convectors turned out to be safe. But what happens if a flammable object gets inside? A large amount of dust can accumulate inside the heater, as well as various unwanted objects, such as large pieces of paper, fabric, matches, and the like, which naturally should not be there. For example, a child who is playing can put them there. We will carry out a number of tests with flammable materials to assess the possible risks. Let's start with paper napkins.

Before starting the test, we tried to accurately measure the temperature on the surface of the heating elements. The laser pyrometer showed from 280 to 330 degrees Celsius for the “stitch” and from 180 to 240 degrees Celsius for the “hedgehog” at different points. The difference in temperature turned out to be quite significant!

Paper napkins

We disassembled our convectors, again armed ourselves with paper napkins and began throwing them on the heating elements.

A heater with a heating element like a stitch set the paper on fire almost instantly.

Interestingly, napkins soaked in alcohol or solvent caught fire only after 3-5 seconds. The flame was much higher.

The main danger of this situation is that burning pieces of paper, rising upward due to the heated air during combustion, can fly out of the device body and land on flammable objects in the room. It is also possible that fire or hot pieces of paper falling to the floor through the lower grille of the convector can get into the cracks between the parquet boards, where dust usually accumulates, which poses a risk of fire.

After placing the napkin on the hedgehog-type heating element, 30 seconds passed, but almost no visual changes were noticeable.

60 seconds have passed. The paper began to turn yellow.

Two minutes. The yellowness has increased.

Three minutes. Even more yellow.

Three minutes. Even more yellow.

Ten minutes. There are more scorch marks, the smell is strong and distinct.

And-and-and-and-and, finally, an hour passed. Our napkin lay on a working heating element for a whole hour and never caught fire!

Let's repeat the experiment with napkins soaked in alcohol and solvent. Here the picture turned out to be approximately the same.

One minute: no change.

Two minutes: yellowish color and beginning of charring, appearance of a faint odor.

Five minutes: charring continues, distinct burning smell.

Ten minutes: charred edges.

Thirty minutes: clear signs of charring, but no signs of fire.

Well, the results speak for themselves. In one case, we got an open flame in a matter of seconds (or even instantly). In the second, the fire never appeared. Let's continue the experiments.

cotton wool

Pieces of not too dense cotton wool look very much like dust balls.

Let's try placing cotton wool on the heating element and see what happens to it.

We check the stitch: put a piece of cotton wool and note the time. Here's what we saw after just two seconds:

And here — after three:

The result is more than eloquent.

What happens if you put cotton wool on a hedgehog heater?

The cotton wool began to char within a minute. The smell of burning appeared almost immediately.

The cotton wool continued to char and after two minutes...

...and in five.

However, it didn’t start to burn, either after ten or twenty minutes. Which, in our opinion, is more than enough to smell the burning smell and turn off the convector. Although it was quite charred on the bottom.

Matches

Matches are not a toy for children. Everyone knows the banality. What happens if a match gets inside the heater? For this test, we took two matches — one whole, and the second with a cut head. We placed them on the heating element and began to wait.

In the case of Stitch, the match with the ignition head ignited instantly.

The match without the ignition head began to smolder almost immediately, here is a photo after 20 seconds.

In 40 seconds...

In one minute.

...in two minutes.

At this stage, the match had completely decayed. Another five minutes — and it will differ little from a completely burnt match with the igniter head.

We again assess the fire danger as high: a burning match can easily fall through the grate at the bottom of the convector.

Now let's put two matches on the hedgehog heating element. The incendiary head ignited in a couple of seconds

A match without a burning substance began to slowly smolder in the same way. True, this time it is much faster. Apparently, the reason for this was the large contact area between the wood and the heating element.

15 seconds have passed...

One minute: the match has completely turned black.

Finally, two minutes: an almost completely decayed match.

Then the match continued to smolder slowly, but no open flame appeared.

From this experience, it can be concluded that when throwing matches inside a running heater, they will light up, but small wood chips will most likely only smolder and give off a burning smell without causing an open fire.

It should also be noted that burnt or decayed pieces of paper, cotton wool, or wood that fall on a hedgehog-type heating element will most likely remain inside the convector body due to its X-shaped shape, which helps retain such materials inside the device.

conclusions

When we started researching this topic, we were confident that discussions about the fire safety of various convectors were largely part of the marketing strategy. You can often come across strange claims made by marketers about modern technology.

A heater, at its core, is a rather conservative device, and its performance directly depends on one parameter — power. But sales of new models require arguments in favor of the fact that new convectors are much better than old ones.

It turns out that modern tens, such as hedgehog, do have a number of advantages over older types, such as stitch.

Of course, there can be no talk of “increased heat transfer” or “saving electricity”. However, in terms of fire safety, the hedgehog can really outperform other convectors using stitch.

Simply put, any potentially flammable object (paper, matches, cotton wool, etc.) that gets on the heating element of the convector will flare up instantly. In this case, burning particles can escape from the housing along with a flow of warm air or fall through the lower grille.

In contrast, a hedgehog ten is likely to keep such items inside the case. Its X-shape contributes to this.

When we conducted experiments, we saw that if a match hits the heating element of the convector, it instantly lights up. However, small wood chips begin to smolder and emit a burning smell, but do not cause an open flame.

Moreover, potentially flammable objects (paper, cotton wool, fabric, etc.) that fall on the hedgehog heating element will most likely smolder for a long time and probably will not ignite. Even if a fire does start, it will not happen immediately, but after some time. This gives the user the opportunity to smell the burning smell and turn off the convector in a timely manner.

In addition, the temperature on the hedgehog heating element was lower during operation of the convector, which, presumably, should reduce the feeling of overheated air and the smell of burning dust getting inside the case. However, our measurements showed that the temperature at the point where the heated air exits the convector is almost the same, regardless of the type of heating element.

Thus, if you want to purchase the safest possible convector, then you should give preference to devices with a monolithic heating element, such as hedgehog. It is also important to make sure that the convector is equipped with overheating protection and automatically turns off if it falls.

All of the above recommendations may not seem very original, but after our experiments we were definitely convinced of significant differences between different types of heating elements.