Reptile & Amphibian Forums

I need to heat some glass vivs.I use flexwatt along the back but its not enough(set around 90 degrees).Because they are for arboreals with high humidity needs I dont have screen tops.I wanted to just add some heat by having a bulb on during the day.
Can I hang a light above the glass a few inches and not have the glass crack.Could I use a low wattage bulb in a fixture sitting directly on the glass?
I only need to get the ambient air temps up about 10 degrees without drying out the tanks.

What exactly causes cracking? Is it the high heat or the fluctuations or what?

I could always just buy more flexwatt and run a longer strip, would that help get the temps up?
BTW I already have three sides of each tank insulated.These are 40 gals set upright.

Heat in one spot while the surrounding glass is cold can cause a crack in plate glass over time, but the hotspot has to get pretty hot.

Anyway, have you tried insulating the top of your tank with something like 3/4 inch foam insulation? I have found that insulating the tops of cages helps a great deal with heat retention.

You can also use fiberglass insulation behind the flexwatt (read the temp limits on the insulation however.) They use fiberglass insulation in small halogen fixtures to keep the heat going one way. This will keep alot of the heat produced by the Flexwatt from being wisked away by moving air. This is your problem: too much of the heat energy is going elsewhere - sucked away by cooler surroundings.

I don't think a light above will be as effective as you think, being that heat rises. You can try aiming a spot bulb at an angle hitting the side of the tank. Or tape a strip of Flexwatt on the tank side as well (at least during the cooler months). But I think the suggestions above will go a long way.

Chris is right, it is a heat differential that can potentially cause glass to crack. If the glass is uniformly heated, at a reasonable rate, you shouldn't have any problem. Or if the temperature difference between a hot area and cold area isn't extreme, you shouldn't have a problem. Unfortunately, it is dependent on several factors, so there is no easy answer to let you know if you'll have a problem or not.

Believe it or not, thick glass can be more of a problem, since glass is also an insulator.