Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The concept of heating the substrate is for better water movement, thus better exchange of oxygen, fertilizers and so on throughout the DSB.
However, aquatic plants do a really good job of gas exchange without you having to provide power to heat the substrate. As Hoppy suggests: Keep the plants thriving, spend your money on CO2, good lighting, and they will do the job for you.