Heater temp doesn't match thermometer temp?

[abrage22]

I've always used Aqueon Pro heaters, but there's always been one problem. It's never in match with my little coralife digital thermometer. I've got the heater set at 80 because that's what gives me a 74 degree reading on the thermometer. I trust the thermometer more because it always matches our house temp exactly when I test it with the thermostat.
I'm looking to get a pair of German blue rams soon, so I need to know, and have the temp right on where it needs to be (78+). Should I just crank the heater up more? Anyone else dealing with the same thing?

 

[smallfry53]

I have never used aqueon heaters, but I think that is typical for the temp. not match what the dial says. I slowly increase the temp. a degree every day or so to get ready for the gbr. If you really want to make sure, you could put another thermometer in to see if they match.

 

[Lt.]

I don't know what brand my heater is, as I got it second hand with a tank I bought, but it reads 82 degrees, when my current thermometer, and every other thermometer I've tried, reads 78 degrees.

 

[shellieca]

I have the same problem in my 46g with an Aqueon heater. It currently is set at about 84F but both thermometers in the tank say 76-78F, depending on if the lights are on. I didn't have this problem until I switched from an HOB to a canister filter. I'm going to try adding a second heater to see how that helps.