Boiler replacement strategy
We have a 1978 split level located in southern coastal Maine. Reasonably insulated (6-inch walls), reasonably well maintained with a 22-year-old 4-section Burnham boiler for baseboards and domestic hot water (the house originally had electric baseboard heat and was converted to oil).
Inspired by the promise of rebates, we purchased two heat pumps about a year ago. One upstairs, one downstairs.
Performance has been… OK. We’re trying to make the heat pumps our primary source of heat, but we still need the boiler on colder days when the outside temp drops below 30 (my wife likes a warm house) and also because the heat pumps don’t reach the bedrooms well.
We will likely need to replace the boiler in the not so distant future. I’m wondering if we can do with with a smaller system (one that would normally be considered undersized for the house), as it is serving largely to boost the heat pumps? Are there other strategies to consider?
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Replies
1. boilers can last a long time, what makes you think it’s replacement time? 22 years is young!
2. Oil boilers don’t come in small sizes. Usually the smallest you’ll find is .6 gph, which is huge for most houses. The technology is limited in this regard.
3. The expensive solution could be an air to water heat pump, which would use the baseboard to heat and could be paired with the existing boiler nicely.
I certainly hope you're right about the age and I don't think replacement is imminent, but I like to plan ahead. We'll see... I'm sure there are many others in the same situation as I am, so maybe the technology for smaller boilers/backup heat systems will advance somewhat in the coming decade.
Oil heat, and boilers in general, are in decline in the US. Propane and gas can be sized more appropriately, but they should still be sized for design load when paired with a heat pump. The hope is that air to water heat pumps can gain more market share in the US for the boiler replacement space.
Consider a gas or pellet stove (or insert if you have a fireplace) in a strategic location. Turn fans on to move the air around. You will at least relieve a good portion of heat burden from the heat pumps (at least 30k BTU, likely more), and it can add to the ambiance of the house.
I abandoned my broken boiler and replaced with a heat pump on one floor of my house. I'm outside Boston so costs are high, but the cost for direct boiler swap was about $10k, and to also replace other components came to around $15k total. Cost for a fireplace insert all in was up to $8k installed. We haven't yet pulled the trigger yet, since we're considering removing the chimney, but we'll definitely add a centrally-located gas or pellet heat source for when the temps drop <30 and we want to augment (for price and comfort). Mind you, the heat pump does keep up, but it just has more variability than the extremely even and comfortable hydronic radiators that I've used most of my life.
An air to water heat pump like the SanCO2 could work well since you already have the distribution, but understand that you may want to increase the BTU output of the baseboards since they're likely sized for 180F water. That said, since you're only using it to augment the heat pumps, maybe they're sized appropriately. The site heatinghelp.com is a great resource for lower temp hydronic systems.
A SanCO2 can't work for this application. It's for DHW and/or extremely low load homes.