Modeling tankless coil in a boiler

Hi Bruce,

That’s a tough one.  I’m sorry we don’t have that option in our standard selections.  We haven’t run into a good resource for modeling that scenario.  As I understand it the seasonal efficiency of the water heating will depend heavily on the house heating dynamics.   You can model a workaround by selecting the Oil Tank Water Heater option and modifying the Recovery Efficiency and Energy Factor yourself. The Recovery Efficiency will be something less than the AFUE of the boiler for heating purposes.  How much less will depend on the size of the system (cycling losses) and how often it is simultaneously in use for home heating.  The EF will be just a couple points lower than the Recovery Efficiency.  The best case scenario would be when you have sufficient oil delivery data to get a good base load estimate.  You could then calibrate the efficiency to match the utility usage.

If you are aware of any good resources on this issue, please pass them along.