redearslider.com

Is it okay to have a high wattage heater on a smaller tank?

Let's say a 300watts in a 20g tank?

Reason is that I don't want to avoid buying another one when I upgrade the tank

yes?no? why?

thank you guys

The higher end and more reliable heaters shut off after a certain temperature so you should be fine with a larger heater.
I'd just double check with a thermometer to be on the safe side.

The only real worry with a heater that powerful on a small tank is if the heaters thermostat malfunctions and the heater gets stuck in the "On" position, it can heat the water to dangerously high temperatures before you notice.

It's rare for this to happen, but I have read multiple cases of heaters malfunctioning and effectively "boiling" the persons fish.

I personally would not do it, as this approach would have resulted in boiled fish twice. Also, heaters are cheap and having a spare, even if under / over powered is handy as they never fail when shops are open.

Over the years I have had two heaters (one cheap and one expensive) jam on without warning, which shows to me the reality of the risk. Over same timescale I have never one fail by not heating at all.

The heaters jamming on had no big/quick effect because I had followed the fishkeepers wisdom of
1. Do not "over power" heaters (I had the right power in the tank for size of tank and room temperature)
2. Have two heaters, so any jaming on / off has a slow effect (i.e. 2x 150 w rather than 1 x300w).

Problem is I am now a bit worried. With new setups, all my tanks (turtle and fish are single heater only - must put the new batteries into the temperature monitors, so the alarms will go off if it over / underheats).

I agree with seanwb, get a smaller 150W heater now and when you upgrade tanks just get an additional heater. Definitely safer than using one large heater.

Depending on your room temperature you may be able to get away with as little as 50w.

Google "how many watts fish tank heater" for sites to help. Remember to half tank size if it is only 1/2 full of water.

There are different views, but rule of thumb is about 5w per gallon of water, less if in a warm room, more if somewhere very cold.

In my office , the tank has 5w per gallon of water, and the pond 2.7w per gallon. Neither heater stays on for very long, therefore I could get away with less.