<p>In the case of 3D Printing, it's going to be faster to cool the radiator by blowing out the heat from the source.</p>

<p>The idea is that you're trying to get rid of as much heat as possible in the quickest means possible. By blowing away from the radiator, you're allowing the ambient temperature to cool the hot air being blown out.</p>

<p>If you were to blow the ambient air towards the radiator, the blown air will warm slightly as it is overwhelmed by the heat of the radiator. Even though the ambient air may be cooler, it will take more time to cool off the radiator.</p>

<p>Example of bad airflow, which will take much longer to cool the radiator:
<a href="https://i.sstatic.net/N6U9u.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/N6U9u.png" alt="enter image description here"></a></p>

<p>Example of good airflow, allowing the hot air to be quickly cooled by the ambient temperature of the build space:
<a href="https://i.sstatic.net/RRqeg.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/RRqeg.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2017-01-10T08:37:48.850Z
I don't dispute the conclusion, but I think its misleading to talk about ambient temperature. All that matters to the heatsink is the air passing its fins. Both cases mix 'new' air with the already heated air.
Sean Houlihane
CC BY-SA 3.0
2017-01-10T15:15:52.347Z
@SeanHoulihane I see what you're saying and I think I agree more with darth pixel's answer. I was coming from the perspective of a machine with a heated build plate, where the ambient temperature is still about 90&deg;F (more if enclosed).
tbm0115
CC BY-SA 3.0
2017-01-09T17:46:06.147Z
2017-01-09T17:51:47.373Z
2017-01-09T17:51:47.373Z
tbm0115
<p>Getting hot air from the radiator is definitely wrong idea because of few reasons:</p>

<ol>
<li>hot air can damage your fan (as they are usually not heatproof). Cold air cools the fan</li>
<li>cold air is denser so fan can suck more cold air than hot air so cooling is more efficient (fig A)</li>
<li>in terms of plug of radiator (with dust) it's much better to try to push cold air into plugged fan (fig C) than to suck the air from it (fig B). When flow is decreased there is higher possibility to damage the fan as it doesn't cool itself</li>
</ol>

<p>Of course we are talking about 3D printers with small plastic fans. Please notice (almost) all fans construction: they are designed to get air from the top of the fan and push it to the bottom (this construction prevents damaging/plugging fan motor by dust)... and their mounting wholes (or clips) are usually... naturally suggesting to direct air to the heatsink)</p>

<p><a href="https://i.sstatic.net/DMoSn.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/DMoSn.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2017-01-09T19:39:41.550Z
2017-01-13T08:42:22.143Z
2017-01-13T08:42:22.143Z
darth pixel
<p>I've build a 3D printer from sourced parts and mounted the hotend cooler to blow air over the heatsink. </p>

<p>Talking to a friend, he said it's better to reverse the airflow over the heatsink, but couldn't give me an argument other than everywhere he saw it was like this: all coolers are mount to suck the hot air away from the heatsink.</p>

<p>Is it one way better than the other way ? And if so, why ?</p>

CC BY-SA 3.0
2017-01-10T15:41:14.867Z
I think it also depends on th design of the radiator and how the fan is mounted on it. Some pics?
Gunslinger
CC BY-SA 3.0
2017-01-10T19:12:32.390Z
I am very confused if this radiator talk. A radiator like my car has in not in my printer. Do you mean the heater element? Ie the hotend or heated build plate? Or do you mean the cooling fins? That could kind of be called a radiator. In that case blow on not suck. Does sucking at your hand cool it?
MakerModder
CC BY-SA 3.0
2017-01-13T12:20:25.347Z
It is unclear to what you are referring to, by your use of the term "radiator" - Could you add a photo of the "radiator"? Do you mean _heatsink_? Or have you installed an additional cooling mechanism?
Greenonline
CC BY-SA 3.0
2017-01-13T14:56:49.843Z
Sorry, yes I mean heatsink. I'll edit the question
Nicu Surdu
<hotend><cooling>
Blow vs suck air over hotend's heatsink
Nicu Surdu
# Blow vs suck air over hotend's heatsink

(Asked by: username_0 on 2017-01-09)

I've build a 3D printer from sourced parts and mounted the hotend cooler to blow air over the heatsink.

Talking to a friend, he said it's better to reverse the airflow over the heatsink, but couldn't give me an argument other than everywhere he saw it was like this: all coolers are mount to suck the hot air away from the heatsink.

Is it one way better than the other way ? And if so, why ?

**Tags:** hotend, cooling
> **Comments:**
> **username_1**: I think it also depends on th design of the radiator and how the fan is mounted on it. Some pics?  
> **username_2**: I am very confused if this radiator talk. A radiator like my car has in not in my printer. Do you mean the heater element? Ie the hotend or heated build plate? Or do you mean the cooling fins? That could kind of be called a radiator. In that case blow on not suck. Does sucking at your hand cool it?  
> **username_3**: It is unclear to what you are referring to, by your use of the term "radiator" - Could you add a photo of the "radiator"? Do you mean _heatsink_? Or have you installed an additional cooling mechanism?  
> **username_0**: Sorry, yes I mean heatsink. I'll edit the question  

---

## 2 answers

### Answer by username_6 on 2017-01-09. Score: 6 | Accepted answer

Getting hot air from the radiator is definitely wrong idea because of few reasons:

1. hot air can damage your fan (as they are usually not heatproof). Cold air cools the fan
2. cold air is denser so fan can suck more cold air than hot air so cooling is more efficient (fig A)
3. in terms of plug of radiator (with dust) it's much better to try to push cold air into plugged fan (fig C) than to suck the air from it (fig B). When flow is decreased there is higher possibility to damage the fan as it doesn't cool itself

Of course we are talking about 3D printers with small plastic fans. Please notice (almost) all fans construction: they are designed to get air from the top of the fan and push it to the bottom (this construction prevents damaging/plugging fan motor by dust)... and their mounting wholes (or clips) are usually... naturally suggesting to direct air to the heatsink)

[![enter image description here](https://i.sstatic.net/DMoSn.png)](https://i.sstatic.net/DMoSn.png)


---

### Answer by username_4 on 2017-01-09. Score: 1

In the case of 3D Printing, it's going to be faster to cool the radiator by blowing out the heat from the source.

The idea is that you're trying to get rid of as much heat as possible in the quickest means possible. By blowing away from the radiator, you're allowing the ambient temperature to cool the hot air being blown out.

If you were to blow the ambient air towards the radiator, the blown air will warm slightly as it is overwhelmed by the heat of the radiator. Even though the ambient air may be cooler, it will take more time to cool off the radiator.

Example of bad airflow, which will take much longer to cool the radiator:
[![enter image description here](https://i.sstatic.net/N6U9u.png)](https://i.sstatic.net/N6U9u.png)

Example of good airflow, allowing the hot air to be quickly cooled by the ambient temperature of the build space:
[![enter image description here](https://i.sstatic.net/RRqeg.png)](https://i.sstatic.net/RRqeg.png)

> **Comments:**
> **username_5**: I don't dispute the conclusion, but I think its misleading to talk about ambient temperature. All that matters to the heatsink is the air passing its fins. Both cases mix 'new' air with the already heated air.  
> **username_4**: @SeanHoulihane I see what you're saying and I think I agree more with darth pixel's answer. I was coming from the perspective of a machine with a heated build plate, where the ambient temperature is still about 90&deg;F (more if enclosed).  

---

