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zoning new oil boiler system
This is my first post so here goes. I am currently heating with a coal boiler 2 pipe gravity system and a oil boiler backup that I haven’t used in years, that looks to be plumbed in such a way that circulates the heated water into the coal boiler and gravity takes over to move the hot water through the system to the radiators. The flue is in need of repair so I have been thinking about removing both boilers and installing a new flue sized for a new oil boiler. If I do this I'm thinking about going to a micro zone system. I'll remove the gravity piping (to remove all that unnecessary mass and water) and replace it with pex to a zoning manifold with thermo electric actuators and install thermostats in the rooms according. I would have 5 zones on the first floor (approximately 1200 sg ft) and 3 on the second floor (590 sq ft) and possibly add heat to the basement (1200 sq ft). I’m thinking and Buderus G115WS 85K BTU DOE boiler supplying a 50 or 75 gallon buffer tank and using outdoor reset mixing valve on system loop and possibility ODR on the boiler also if there is any energy savings in doing so? I have many days that heating with the coal boiler only requires 100°F water and I’m thinking 150° for “design day” weather. I’ll use the ODR valve to set the best water temp for the radiators (sort of what building the correct coal sized fire does now when you think about it) and the boiler ODR to set the best water temp for fuel savings. Does all of this sound doable? I’ve done some rough heat load collections and the max btu of boiler is so close when figuring in the basement it sort of make my wonder if I shouldn’t go bigger? Currently the foundation walls are not insulated and should I heat this space I would do so, when I did the calculations I did them w/out insulation so that would help bring the heat loss down and when doing a system like this where every rad is practically its own zone and can the boiler output be reduced by a certain percentage? Thoughts?