Tank heater in cold room

Question
I have a 50 gallon that I have almost set up, with a 60 gallon capacity underwater heater in it.  It has a biological (hanging on the back)
wheel filter, and an undergravel filter.  I've kept fish for many years, and I haven't put the fish in it yet because it is sitting in a foyer
that stays at about 38-40 degrees in the winter, and the heater doesn't seem to be able to heat it to even 70 degrees, even though it's rated at that gallon capacity.  I have goldfish and koi, which would probably do fine with the lower temperature, but the bacteria in the biological filter don't do well at those temps.  What is the solution?

Answer
Hi G. Shulz;

Add another heater of the same wattage. Together they should do the job for goldfish and koi. For a 55 gallon in a normal low room temperature of 60 to 68 you need at least 275 watts to get it to 85 (if you ever need it that high). This is 5 watts per gallon. I usually double it if the room is below 50. If they were tropicals you might need to triple it, but see how it goes with your cooler water fish. I think double is enough, which equals a total of 550 watts of heater power.

Followups welcome.

At Your Service;
Chris Robbins