Startup Hardware Research, how to?

We've seen the Y Combinator how to start a startup videos and blogposts, but one topic I can't find much information on is how to do market research when your idea depends upon some hardware.

For instance, let's say I want to build an app for pressure cooker users. I have a big list of pressure cooker manufacturers, how can I find out how many of my customers exist (people in the US, Europe, and world that own pressure cookers)? It's not straightforward to me how to figure out how many pressure cooker owners there are in the US.

Another example could be for treadmill owners. Let's say I want to make an app for this customer segment. I can imagine using other "treadmill owner" apps to estimate my customer base, but is there a way I can find out how many people bought a treadmill, or a pressure cooker, in the last 5 years?