I recently purchased a home with a Greenwood 100 installed in an outside shed to heat my house. I'm just learning about all of this, but I've been told it is a closed system. I've been doing prep work getting ready to fire, and my instruction manual talks about checking the transfer fluid levels routinely and draining/changing it every couple of years. Here's the problem - I don't see this gauge anywhere on my stove. Plus, I don't have the "fill port" shown in the diagrams. The previous owner (who is a contractor and knows more than I do) said that the system doesn't use the transfer fluid because it is closed. Greenwood's website hasn't been helpful and, so far, I haven't been able to talk to anyone from that company. The stove is about three years old. So, my questions: are some systems run without this transfer fluid? If so, is it okay to do this? If I should run it with the fluid, any ideas where the fill port would be hidden? Thanks for any help that you can provide.