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Thank you. It wouldn't surprise me that the heating system is oversized. Why would someone spend extra time to properly size a system and make less money off the deal. Throw 4x the gear at the solution, never have a not enough heat call back and make 4x the markup.

I'll review the heat loss article. The building is going to be modeled in CAD soon so I might be able to leverage that and throw it into LoopCAD and do the heat loss calculations there without too much work.

At this stage I'd just like a quick easy win. Throw something residential in for pre-heating if possible and save 10% pay back in 10-20 years is fine. Eventually the boiler needs replacement and it looks like high efficiency gas is likely to be the best choice given the heat loads. I had one quote just for the boiler of $52,000 and that is without installation. We'll likely run to failure for the existing heat plant - really I think until one of the 4 units dies I won't be serious about putting the work in to figure out a replacement plan. Yearly gas bill is ~$26,000.

My napkin numbers.

Going from the 80% to a 96% ( assume you only get 90% ) would save $2000 a year ( some of that gas is for the domestic ). $52k for the boiler assume optimistically $26k for install? would be a 39 year pay back which is too long. I like mechanicals but right now seems like doing things to decrease heat loss are going to be the biggest bang for buck.

Assumption is that COP of 4 would mean 50% cost of the BTU from heat pump.

Swapping 864,000 BTUs over to an a2w heat pump would require more land space, more money and more electricity than the building currently has available. Ideally we'd start with something and see how it goes before 100% committing. Too often projects are contemplated in an all or nothing scenario resulting in nothing.

We have our domestic preheating with 3 HPWTs before final heating with a gas hot water tank. The proterra units are each 4200 BTU. The gas hwt is 385,000 BTU. While the HPWTs aren't providing a huge portion of the hot water it did enable us to reduce from 2x 385,000 BTU tanks to one and leave the redundant one as backup. The setup likely was overkill to start with but the hybrid solution has saved ~10% off the overall gas bill with minimal impact on the electric side.

In order to justify the project I'd want to see making the money for the installation back in 10-15 years (ignoring interest). I can't see a full swap ever paying back so a full swap point could only happen once the current hydrotherm hits end of life. 1985 cast iron - it might be around for another 25 years? The heat pump tech is still in flux so it is nice to start small and realize the improvements in the technology rather than bleed out on the cutting edge.

The HPWTs are an easy win as they are used year round whereas the boiler is only used Oct-April and I think the heat pumps will generally have a hard time heating water at 127F a lot higher before the boiler while maintaining a high COP.

My sense is that given the project requirements a heat pump can't work for this application but I thought I'd post and get a sense from the experts. Can assume 46F+ as air temperature during the majority of the heating season.