Portable water heaters?

[fripclaksid]

I do a small amount of aquarium maintenance and I sometimes run into problems because the boiler would be too small or they wouldn't even have hot water. Is there a portable water heater? All the portable water heaters I've looked into seem to be too large and some even needs propane. Do you guys have any input? Thanks in advance.

 

[rkaragozler]

These are the ones we use at work, one problem with them is recovery time, it takes too long, they have on demand water heaters but very expensive,
http://www.amazon.com/dp/B0006GVO12/?tag=reefs04-20