Taming the Heat:

Keeping a  small vivarium cool without fans

I love compact fluorescent lights but the heat they produce can be a problem, especially in small vivaria.  A 10 or 20 gallon vivarium fitted with a single 36w compact fluorescent fixture can easily exceed 90°F (30°C) in a room at typical daytime room temperature.  Unfortunately, venting the vivarium to allow the heat to escape also allows humidity to escape so it be difficult to vent a vivarium enough to maintain optimal temperatures and still maintain adequate humidity.  One approach is to attempt to cool the lights by blowing air across them with a fan but fans can fail, add complexity to the system, cost money, consume electricity, and produce noise.   The noise of a dozen small computer fans whirring in a room can be substantial.   Following are pictures and temperature data for a passive cooling light ventilation hood I developed for small vivaria.

The test vivarium is a 20 gallon tall (51cm W x 48cm H x 25cm D) fitted with a single 1 x 36w compact fluorescent fixture with ESU Desert Sun 7 CF bulb.  The original hood contained a row of 6 - 6.5cm diameter ventilation holes along the rear top (see image below) and the fixture was mounted in the hood with no barrier between the bulb and vivarium space.  Maximum daytime temperatures routinely exceeded 88°F (31°C).

First Modification

The first modification was to install the acrylic light shield shown in the images below.  The shield was bent from a sheet of  0.125" (3mm) thick Solacryl heated with a propane torch and bent over a 90° angle form.  The dimensions of the shield are just enough to clear the fixture (I always flatten the light reflectors about 50% after they are install) and create a tight fitting transparent barrier between the fixture and vivarium space.  The shield is attached to the hood with 6 stainless steel pan head screws.

Bottom view showing shield installed to top and rear of hood.

Front view with front access panel open to show installed shield.

Installation of the shield alone reduced the heat inside the vivarium but not enough.  Daytime maximum temperatures typically ran about 85°F (29.5°C).

Final Modification

The final modification was to drill 3 inch (7.5cm) holes in the hood at each end of the light shield (see image below) and two 1 inch (2.5cm) holes in the top front corners fitted with ventilation caps (image below and at top).  The large holes in the end are the key to the ventilation because they allow a chimney effect to form inside the now sealed light compartment.  Warm air from the light rises through the row of vents along the top rear and draws in fresh cool air through the end vents.   The two 1 inch vents allow some heat to escape directly from the vivarium.

The finished hood.

Test Results

Temperatures inside the vivarium and in ambient room temperature were monitored for two weeks using a digital indoor/outdoor thermometer with remote probe placed about 1 inch (2.5cm) above the substrate surface.  Temperatures observed throughout the day were typically in the range of 70°F -77°F (21°C - 25°C) with the following extremes recorded over a two week period:

It can be seen that the final system maintains temperatures at the vivarium floor within a few degrees of ambient room temperature despite significant heat output from the lamp.  Additionally, the vivarium is obviously still young and not grown in with plants yet.  As the plants develop and mature, leaf shading should provide greater variability of temperatures throughout the vivarium allowing the frogs to seek optimal temperatures as needed.

The real test, however, is whether the frogs find it suitable.   Just two weeks after introducing a male pumilio to the vivarium, he began calling.   This is significant because this frog has not been observed calling for about a year and has been housed in a vivarium similarly planted and the same size as this one except that normal daytime temperatures were about 10°F (5.5°C) warmer without the acrylic shield and ventilation.