We live in the D.C. area and have a small 10x10 fully insulated greenhouse attached to our home. Until recently was heated by heat pump but 15 year old pump has failed (heat exchanger leaking and condensor may be too). We use the unit only to keep at about 50* in the winter - no a/c needed for plants. Q: what would be best replacement? Electric baseboard, wall forced air untit, gas space heater, new heat pump? Size?