My house has redundant systems for both domestic hot water and hydronic heating (baseboard and radiant floor). I can pick and choose which system I'm running. We also have several mini-split heat pumps with solar making our average $/kwh around $0.129. My goal is to pick the cheapest system(s) to run this winter.
- System 1: Buderus oil boiler with accompanying hot water tank (87% AFUE).
- System 2: Baxi tankless propane boiler (95% AFUE)
- System 3: Mini-split heat pumps (Fujitsu -15)
We live in Zone 6 climate so it gets pretty cold here.
So heres my question to you all. If we are relying on our heat pumps for most of our heat does it make sense for us to use the tankless propane or oil boiler for DHW and/or backup heating?
There are a bunch of articles on how to compare propane to oil such as this one. However, none of these articles factor in the additional potential efficiency gains you get from a tankless. According to energy.gov they claim anywhere between 8% and 34% gains for DHW. I haven't see any such claims for heating.
My gut tells me I should run the heat pumps and use the tankless propane for both DHW and backup heating. However, using todays fuel prices in my area the math suggests it would be nearly half the price to run the oil boiler for DHW and backup heating.
- | Oil | Propane |
---|---|---|
$/gal | $4.10 | $4.87 |
BTU/gal | 137381 | 91452 |
$/100k BTU | $2.99 | $5.33 |
$/100k AFUE BTU | $3.43 | $5.61 |
Does the tankless propane boiler provide any additional efficiency gains over the oil boiler that would make these more comparable options? To be even remotely comparable the tankless propane would need to be nearly 60% more efficient which sounds unlikely but maybe that is the case since it would be just for DHW and backup heating.
Edit
- Included AFUE and updated prices
- Specified heat pump type and solar info