Apr 06, 2022 · Espar D2 vs D4. You may be wondering why we recommend the Espar D2 over the Espar D4. In short, the Espar D4 is overpowered for the van, and as a result, it won’t run at high boosts very often. This means that the excess fuel that’s going into the heater doesn’t get burnt up. That excess fuel will sit inside the heater and the heater will