----- Original Message ----- From: "Olin Lathrop" Subject: Re: [EE] Tank Temp Control Redux > For example, let's say the temperature drops 2C/hour at 50C. 2C/hour is > 3.6F/hour. You have 80 pounds of water, so that's 288 BTU/hour = > 304Kj/hour > = 84.4j/S = about 85 watts. If that's the case, a 2.5KW heater should > still > be fine. If Mike is the patient type, and the loss does turn out to be around 85 watts, then the 100W heater ought to work pretty well. Just turn it off for a little while each day. Of course, Mike may grow a rather long beard getting it up to temperature in the first place..... It surprises me that I didn't jump on the "do the math" thing in the first place. I'll be in Germany next week teaching model building. While we talk about designing experiments to uncover the model, the first rule is that if you have a first principles model, you use it. It is incredible how many people will do an amazing amount of work to avoid cracking open a textbook. --McD -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist