choosing the right aquarium heater for discus

[Lioness]

I'm looking at ways to keep my discus safe and I have a question about using multiple heaters. I know having two heaters is beneficial in case one fails, but I'm wondering if it will also impact my energy usage. Will using two heaters use more or less energy than using just one? I'm thinking that one heater set to 28C might be constantly switching on and off, whereas two heaters might provide a more stable temperature and use less energy overall.