Hallowell International was founded in 2005 and went out of business in 2011. They had a hot product called the Acadia which was an air source heat pump that could heat a house down to -32 degrees F! Their claim to fame was that you didn't need to have a back up heat source if you installed their heat pump. Unfortunately, the product was plagued with a lot of technical problems, thus forcing them to close their doors.
Chris Brooke, Founder of FurnaceCompare.com, did some extensive research on the topic. His article is on this link: https://www.furnacecompare.com/manufacturers/hallowell.html
If you have an Acadia heat pump, this link does have a list of HVAC Contractors that may be able to help you.