Three new tenants leased warehouse space on the first floor of Four Townsend West in Nashua this month. Howtek Inc., which uses its digitizing systems to reformat images for the medical and graphic art industries, will move into 6,000 square feet for four years. His Mercy Christian Fellowship, a religious organization, and Mania Technologies, a supplier of printed circuit equipment, both leased 3,000 square feet for three years. Bill Luers of Tamposi Nash Real Estate Group Inc. represented the landlord, 4 Townsend West LLC, and the tenants in these direct deals.