The hot water heaters are STD 1" pipe. but on the other had I would stay away from using them as heating sources, because I have been there done that. Any particles that are in the oil will stick to the element since it gets so hot. Even if you take a 3000-4500 watt 240v heater and cut it down to 110 which will take the wattage to 1/4th. IE a 4500watt 240v is 1125watts at 110. heat vs surface area scorches the oil and the bits suspended in it. Go on Ebay and search for a Chromalux heater. You can use a 240v just divide the wattage by 4 to see what rating it is They have thermostats built in and have a knob right on the outside with the temp settings. I have a 240v 3500 watt one running on 110 so its like 875 watts, but its also 72" of 3/8" brass tube heating surface vs 24" of 1/4 metal tube on a water heater, so no scorch. Dont know what else you did ask, but I will get back to you when I read your post again.