Anyone can help me figure out what size buffer tank would be best? My wood boiler is a closed system with a 23 gal capacity, will be about 75ft from house. Initially to run a heat exchanger in plenum 16 x 18. Like to add some other circuits like to water heater and garage. The info i found on boiler 120,000 working to 140,000 max btu capacity and the exchanger is rated 115,000. My house furnace is a hi efficiency 80,000 and barely keeps up when its good n cold outside. Looking for ideas without breakn the bank, thinking of using an elec water heater for the tank. Im capable of doing the work but my math skills not where they should be for calculations.