I use Mathcad 2015 and when I calculate thermal resistance in K/W I get output in completely different complicated units using meters and seconds. How to force Mathcad to give me result with desired units?
Please tell us more about this Mathcad 2015, or did you mean Mathcad 15...?
When you evaluate an expression, there's a placeholder for units behind the result value. You can fill in the K/W and the other stuff will disappear if unit of the result actually is K/W.
You may want to check what the setting for units is that you use with your worksheet (Tools->Worksheet Options -> Unit system). It can be set to SI, MKS, US, CGS or none if I'm not mistaken.
You may be interested in this topic "Design of a small residential heating system" that you find doing a search in "search all content", there are many custom units of measure.