Hi all, the attached picture shows the present setup (red line) and proposed change (black line) I was told would help me with my dilemma. With my current setup (red line), for the most part, when the temps are above zero, the house stays warm and comfy but when it gets below zero, especially at 20 below with a strong wind, my current setup cannot keep up with the demand in the house. The temp in the house will not get above 65 although the stats are set at 70. The water coming into the house from the OWB is through 1 inch Thermopex is ~195ish, the return ranging anywhere between 160/170, depending on load. I have Grundfos 26-99 at the OWB on the number 3 setting. The feed and return manifolds are 1 1/4 inch copper 3/4 inch zone valves for each zone. I was told the proposed (black line) will solve my problem. I cannot wrap my head around how the proposed change (black line) will do this. Can any of you pros offer some insite? Roger