heater sizing recommendations are way off

[fryman]

I have a ~120gallon setup, so based on recommended heater sizing I got 2x300W BRS titanium heaters on an inkbird controller. I also have an Apex for backup temp monitoring. The BRS website recommends 300W for "up to 100gal" and also put out a video awhile back that suggeated 2 smaller heaters is better than 1 big one. The logic made sense to me, although in retrospect maybe 2x200W heaters (BRS says 200W for up to 75gal) would have been more appropriate. I don't recall why I went with 2x300W.

Anyways, this worked fine for ~4years. A couple weeks ago I had low temp alarms. I checked my equipment, and found that both Ti heaters were not working. I thought it odd, for both to fail at the same time, so I checked power useage from my EB832 and found that only one of them has been working for as long as the Apex keeps records. Looks like one failed an unknown time ago but everything still worked so I didn't find out until the second one failed.

Apparently 300W is more than needed for my setup. Also, having redundant heaters seems kinda pointless, unless I have some way to detect when one goes bad.

So I've been testing the last couple weeks using spare heaters I happen to have on hand: a 150W ehiem, 100W tetra and 100W no-name heater. These 100W heaters are tiny, maybe 4in long and labelled on the box for 10-30 gallon aquariums.

And yet ANY of them is able to maintain 25C for 120G (!). The 150W eheim can maintain 26C. The 100W heaters aren't adjustable and so they turn themselves off at ~25C. They do seem to stay on most of the time at night. Ambient temp is obviously a factor. At night we allow the house to get cooler and yet these tiny heaters still do the job.

This is not what I expected, and got me thinking I may have grossly over-sized my heaters for a long time.

What size heaters do you use? I'm thinking to just stick these two tiny 100W heaters on the inkbird and call it a day. It was surprising to me that this works.

 

[UncommonSense]

I use a single 300w eheim on my 180g (+75g sump)… have done so for over a decade…

You’re 100% right, companies over-sell on heaters as much as they possibly can! (A 13.5g AIO tank breakdown I got recently came with a 150w eheim heater that barely fit in the filtration compartments…)

These heater sizing recommendations would be more accurate for older, poorly insulated homes in winter states… likely in a home with no central heating!

 

[BeanAnimal]

Electric heating elements produce 3.41 BTU per watt-hour consumed.
It takes 1 BTU to raise 1 pound of water 1°F.

A 100 gallon tank and sump, ignoring the mass of rock, glass, etc., is ~100 gallons of water. That’s about 833 pounds; call it 850.

So it takes ~850 BTU to raise the 100 gallon tank by 1°F.
That’s ~250 W running for 1 hour.


If your tank (on the coldest day, with no heater) drops more than 1°F per hour, then you are losing more than 850 BTU/hr. For example, a 2°F drop per hour is ~1700 BTU/hr, which needs ~500 W just to hold temperature.

If you tank loses only 0.5 °F per hour, then your heater only needs to be 125 W to keep up.

The same math can be used to estimate how fast a single “stuck on” heater can overheat a tank, or how a pair of heaters will behave if one fails on or off (overheating or underheating depending on sizing).

 

[The Ugly Phase]

use a 650 watt for my 90 gallon

 

[Tangdora]

1200w on 360 gallons. 3-5 watts is typically a good full of thumb.

 

[JBNY]

As other have said., it depends on what the room temperature is. My sump in in the basement. I never turn the heat lower than 70d at night just because the heaters will be on all night.

 

[BryanM]

For me, sizing 1 heater properly to keep your tank at temp is the most important part. If you undersize and use two heaters simultaneously they will wear out faster and if one fails the tank cannot maintain temp.

So I have two oversize heaters, one is active from 12am-11:59am, the other from 12pm-11:59pm. If the active heater isn't doing its job the other heater will take over.

I would have run two 300w heaters in your tank if it were mine.

 

[KStatefan]

My calculated loss on a winter morning was 168 watts. I have changed pumps so i need to redo this on a cold dry morning. I removed two mag pumps so I am sure I have more heatloss now.

 

[mcarroll]

People tend to oversize without thinking a lot....that just creates potential risk IMO. It shortens the time between failure and fried fish, so less time to react with a fix. Inkbirds and remote notification are nice, but a lot nicer when the window of time for your reaction is measured in hours vs minutes.

But there are cases where oversizing makes sense...a remote sump that's also serving as the heat source for the display tank, for example. Not only do you need a heater that will satisfy the 3-5 watt/gallon "rule" for both volumes of water (and heat losses to both rooms), but you'll have additional losses from the plumbing. So at minimum you'll be at the top end of the "3-5w/g rule", but it could even be more.

Still, it's preferable, when possible, to use just the recommended size heater for each tank on the system. IME it's almost always possible. Then, even in the remote sump scenario, neither heater might need to be oversized.

My calculated loss on a winter morning was 168 watts.

Cool!!!!

Would be interesting to have a KillAWatt on the heater (it accumulates data) to see how closely the caclulation matches actual uasage over a similar period. (I bet it's close!!)

 

[BeanAnimal]

1200w on 360 gallons. 3-5 watts is typically a good full of thumb.

I would suggest calculating the size needed based on a simple temperature measurement drop.

Oversizing a heater means A) rapid temperature swings and B) rapid overheat in the event of an accident.

 

[Freenow54]

I use a single 300w eheim on my 180g (+75g sump)… have done so for over a decade…

You’re 100% right, companies over-sell on heaters as much as they possibly can! (A 13.5g AIO tank breakdown I got recently came with a 150w eheim heater that barely fit in the filtration compartments…)

These heater sizing recommendations would be more accurate for older, poorly insulated homes in winter states… likely in a home with no central heating!

So I am taking from this that a large wattage heater cycles more therefore lessons the life of the I assume thermal switch ? Just trying to have it explained in a better light

 

[Jamie814]

Would be interesting to have a KillAWatt on the heater (it accumulates data) to see how closely the caclulation matches actual uasage over a similar period. (I bet it's close!!)

If you have an apex it does this for you. You just enter your kw rate when setting it up, and it calculates everything plugged into it together or individually per outlet iwth graphs and all. My system costs about $65/month to run slightly more in the winter.

 

[UncommonSense]

So I am taking from this that a large wattage heater cycles more therefore lessons the life of the I assume thermal switch ? Just trying to have it explained in a better light

That’s been my experience with traditional mechanical bi-metallic heater thermostats, yes!

modern digital heater control has made mechanical bi-metallic thermostat failures less of a concern for those just getting into the hobby… however, for those of us with older gear laying around, this nuance is worth keeping in mind!

 

[BeanAnimal]

So I am taking from this that a large wattage heater cycles more therefore lessons the life of the I assume thermal switch ? Just trying to have it explained in a better light

Thermal cycling is hard on the element, tube seals and mostly the switch contacts (typically bi-metal). Ideally the internal thermostat is never used to cycle, but only as a fail-safe.

 

[BristleWormHater]

Theres a lot of factors that go into this, I can think of, humidity, glass thickness, lid type, water flow, & outside air temp can all effect how fast or slow the water heats. I use a 100w on my 25 gallon, It heats pretty frequently as my house is a little colder, especially during the winter because of thin single pane windows, especially the two near the tank. In somebody else's house that 100w heater might only have to heat every 30 minutes or so.

 

[UncommonSense]

Theres a lot of factors that go into this, I can think of, humidity, glass thickness, lid type, water flow, & outside air temp can all effect how fast or slow the water heats.

The insulation of the exterior walls, and ceiling/attic/roof… whether the home is on a concrete pad or has a subfloor/crawlspace (and insulation there)… total non-compartmentalized air volume of the home, etc….

Then there’s the target temp the tank itself is set at… are the tank/sump glass or acrylic… how much other equipment is contributing to heating the water…

It’s almost infinitely complex as an equation!

— I’ve found that a smaller tank heater, and a well insulated/heated structure works quite nicely, at least in the temperate climate here!

 

[Freenow54]

That’s been my experience with traditional mechanical bi-metallic heater thermostats, yes!

modern digital heater control has made mechanical bi-metallic thermostat failures less of a concern for those just getting into the hobby… however, for those of us with older gear laying around, this nuance is worth keeping in mind!

So Enlighten me please how does the digital switch work? Not being smart that is not like me LL

 

[Freenow54]

Thermal cycling is hard on the element, tube seals and mostly the switch contacts (typically bi-metal). Ideally the internal thermostat is never used to cycle, but only as a fail-safe.

Clearly I don't know how a heater cycles Please tell me

 

[Freenow54]

Clearly I don't know how a heater cycles Please tell me

I do know how Bi metal works I looked up the answer on new tech and I got the answer I expected A Thermistor. However I don't understand why this is not a wear part

 

[BeanAnimal]

That’s been my experience with traditional mechanical bi-metallic heater thermostats, yes!

modern digital heater control has made mechanical bi-metallic thermostat failures less of a concern for those just getting into the hobby… however, for those of us with older gear laying around, this nuance is worth keeping in mind!

Most “modern digital” thermostats in context to hobby aquarium heaters are SCR based and minimally designed circuits with no failsafe, the failure mode of an SCR is “on”.

I would never rely on an aquarium heaters on board controller to switch power and maintain temperature.