If using a timber base, such as a thin sheet of MDF, for heat cord… saw or rebate parallel channels, every 2 cm, such that they are fractionally larger than the diameter of the heat cord. Then include two or three channels at right angles, similarly spaced, near the top and bottom edge. You will probably need to gouge out a little of the channel to accommodate the last 2 cm of the cord. The MDF board should be sealed once cut. Three coats of polyurethane or acrylic paint or similar will ensure it does not absorb any liquid wastes. There is absolutely no need to route out the floor of a cage. A small hole drilled at the required level in the back bottom corner will allow the heat to be passed in and then threaded. Am easier alternative is to use coreflute.
Placing a slate or ceramic tile on top has a number of distinct advantages. Tiles have what is often referred to a high thermal mass. They take a lot heat to warm up each degree and as a consequence, they are able to give out a lot of heat to a cold reptile before they cool down significantly. At the same time, they are good conductors of heat and will spread the heat evenly and quickly. Heat that is drawn out of the top will be replaced by heat from within all of the tile. So they make an excellent surface on which reptiles can warm up. They also have that large amount storage to give off once the heat source underneath them is turned off.
The temperature to which the surface of the tile will get depends on the many factors that influence the thermodynamics of a given enclosure in addition to the wattage of the heat cord used. Someone in Qld said they get 40 degrees with a 15W cord. In Perth, in winter (thanks to Snowman), we got 35 degrees on a corflute threaded 15W cord. I have also 35 degrees on an MDF threaded 15W cord with tile on top. The beauty of these two systems is that you can re-thread the cord so that a percentage hangs out the back, to reduce the internal temperature attained.
Wood is a good insulator. If you want the cord to give off heat underneath, then do not use wood as material to hold it. I would suggest using coreflute sandwiched between two tiles. That way you minimise the need for tape, which can create real problems if you don’t have the right gear – aluminium tape. This will also provide structural rigidity. There are some simple metal clips available that will allow you to hold the tile sandwich together nice and firmly – you just need to buy the right size.
At $20 for a 15W cord and $25 for the next size up, I figure you can afford to dabble a bit. I am a strong believer in using the minimum required wattage so that if anything goes wrong with the thermostat, you are not going to come home to baked reptiles.
Given that you are getting a good degree of transfer of heat from the cage below, and that hot air rises, I would be starting with the lowest wattage and seeing how that performs. The reality of life is that determining just the right amount of heating for any given enclosure is, to some degree, a process of trial and error. So start with the minimum likely wattages and build up from there.
I am sorry I cannot be more specific than that.
Good luck with it,
Blue
