Aqua-Hot hydronic heating is associated closely with recreational vehicles. Probably because Aqua-Hot created the first engineered application of hydronic heating for RVs back in 1984. Hydronic RV Heating Products Annual Service Kits 125D Model (Diesel) 125G Model (Gasoline) 250D Model (Diesel) 250P Model (Propane) 400P Model (Propane) 400D ...