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Hydor in-line heater on filter inlet?


11 Aug 2017
Cambridgeshire, UK
i know the traditional way to to place the inline heater is on the filter outlet.

But is there any reason why it can’t go on the filter inlet. Has anyone done this or can explain why it is not a good idea?

I would like to put it on the inlet and co2 inline on outlet. Tank is only running at 22 degrees.



Ps. Is there any other inline heaters on the market? I only know of Hydor.
I tried it once, it's just more prone to getting gunged up and therefore not necessarily working as efficiently.
If it helps I have both heater and atomizer on the outlet. Atomizer first and then heater.
It tends to create air pockets more easily when it's placed on the inlet, but if you're careful when priming the filter and tilt the heater a bit to get all the air out there's no reason you cant do it.
Cheers guys,

I’ll try to leave it on the outlet and see if there’s room for co2 also.

If not I’ll give it a go on the inlet. :thumbup:🙂
Not a pretty picture but this is how I've done it in quite a low height cabinet...


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explain why it is not a good idea?
one possible reason I've read, aside from getting gunked up is not reading correct temperatures (do they anyway?) however you can fix that easily by increasing the temperature on the heater and adding a separate controller such as an Elitech a brand widely used in marines. This one makes things easy as it's pre-wired and is sub £20, I use it on my titanium heaters and they've never failed. They just involve a small probe being added inside the aquarium to monitor heat which really is tiny.

*Check out the Elitech website where at the moment the are £15.99, free shipping and an extra 5% off if you add the code 'EXTRA5' as of 24/12/2019
Ps. Is there any other inline heaters on the market? I only know of Hydor.

There are these Chinese ones you can find on eBay for around £20. ETH300 or something. No idea whether they are good or not.
did you ever do this? was looking at something like this in the future

yes have set it up this way on both ADA and Eheim filters. Seems to be working fine on both.

only concern is long term it may reduce the heaters lifespan due to dirt build up.