Hydronic air handler: tankless water heater or heat pump

I live in Queens, NY and currently have a Burnham boiler (299K BTU) running 2 zones for heat via a hydronic coil on 2 air handlers and 2, 5 ton Lennox units for A/C also using these Lennox air handlers. This equipment has outlived it's useful life and I'm looking for advice on replacing with efficiency and reliability at the top of my list. My questions are:

Should I be considering heat pumps instead of (or in addition to) another heat source?

Rheem has an integrated tankless hot water, hydronic air handler and condenser system, would this work? If heat pump is an option, could it be hooked up to a hydronic air handler?

Lastly, does it make sense to connect a tankless hot water system to a small hot water heater to avoid the wait on a long run (I have a recirculating pump for this purpose today).

Apologies for the long questions, but I really would appreciate some impartial advice.

Thank you.

Those systems are quite large, could be necessary, but that's highly unlikely! First thing is to either analyze your fuel use to try to understand what your real requirements are as a first guess, then probably pay someone to do a manual-J heating analysis to determine what your REAL needs are. Then, and only then, can you size things properly.

FWIW, the only thing excess a/c capacity does for you is cool things off quicker if the building has been heat-soaked for a long time. It is terrible for maintaining a comfortable temperature with adequate humidity control. And, humidity control in Queens is likely a high priority.

A boiler that big could heat a big apartment house...while there may be some houses that need one that big, those people tend to not visit forums for free help! If you read some here, you'll find lots of people stuck with the same thing - excessive capacity for a boiler. This is not uncommon, as most places are too lazy or ignorant to size one properly. For economy AND comfort, a 'right-sized' one is what you want, which starts with a room-by-room analysis of your actual needs.

So, assuming the boiler ~80% efficiency your boiler output is ~ 240,000 BTU/hr, and you have 10 tons of cooling?

That would be about right if this is a ~10,000' brick building with no insulation in the walls, but it's probably way overkill for your actual heating & cooling loads.

First things first- get a handle on what the true heating loads are- a Manual-J heat loss calculation would be the right thing to do, but short of that, let's start with a fuel use analysis, which is sufficient for establishing an upper bound on the heat load, which would also steer us toward a more sensible solution.

If you have a mid-winter gas bill (or is it oil?) with the exact meter reading dates on it, and a ZIP code we can convert your fuel use per heating-degree day into a BTU/hour @ +15F (the 99% outside design temperature for NYC), to better right-size the equipment.

Depending on the condition and size of the ducts there may be other issues if your actual heat loads are 24,000 BTU/hr rather than a large fraction of 240,000 BTU/hr, but let's cross that bridge only when we know the actual loads a bit better. It's one thing to be 2x oversized, another to be 10x.