If you have off-peak water heating service available from your power supplier, you may be interested in newly designed units which will both heat the water you use for washing and provide warm air to heat the milkhouse.
McFate, K. L.
"Heating a Milkhouse with a Water Heater,"
Iowa Farm Science: Vol. 8
, Article 5.
Available at: https://lib.dr.iastate.edu/farmscience/vol8/iss5/5