do I need to install warmboard on the second floor of small house
It really depends on your situation and layout of the home. Some do put radiant on the bottom floor only and trust that will be sufficient to heat the upstairs as well. This is especially true if the upstairs is open and perhaps just a small loft. But the vast majority of the homes we are involved in – whether small or large – use radiant on both floors. More comfort, and greater control of that comfort.
Feel free to send over your floorplans, and let us know about your thoughts, and questions, about putting Warmboard on both floors. We can walk you through the pros and cons and help you make the right decision that is best for you.