Johnstone Supply Gaithersburg is a leading HVAC/R Wholesale Distributor with access to over 70,000 locally stocked products and inventory so you can get it same or next day in most cases. Our product selection is continually growing to meet the needs of HVACR contractors to ensure we have the best brands and technology. Plus, our relationships with hundreds of the industry's top manufacturers give you access to a million special order parts. From equipment, to parts, to supplies you can be confident Johnstone has what you need today. Johnstone Supply: Making it Easier to do Business.