Best system for Duplex I’m purchasing

What type of heating is there now?

Is there a basement or crawlspace? Accessible attic?

Is natural gas available?

KEEP THE STEAM!

Tightening the envelope is your biggest return on investment!

So your going heat pumps.

I was building a 4 plex a while back. Cold climate with hot muggy summers with cheap gas and electricity. Went with ducted heat pumps for each unit simply because we need cooling. The cost delta between a cold climate heat pump and AC only is a couple of dollars and install is the same. Saved having to do gas work, venting and any plumbing.

Top unit has a 1.5ton unit, sandwitch floors 1 ton. No issues with heat. Each place has a small ERV with the fresh air connected to the intake and exhaust from the bath (so no bath fan needed).

Each unit is sub metered so they pay for their own use. More important, everybody has their own thermostat. Operating cost is very low comparable to a place with gas since there is no gas meter fees.

Did install oversized filters so can get 2 years out of one.

Keep the steam as your primary heat source. Over the long haul, it costs no more to maintain and keep in good repair than any other system, and probably less (and less hassle) than heat pumps — as well as greater comfort.

Now what you might want to do, if you have the extra cash on hand, is install heat pumps for the shoulder seasons and for summer air conditioning. They cost a good bit to install — a lot more than a boiler, for instance — and they have ongoing maintenance issues (even the best of them) and a short — 10 to 15 year — reliable life — but they are "modern" and "green" and both of those a selling points.

You want a thermostat in each unit. OK. What I would do is keep the steam as the primary heat, set at a fixed, low temperature — say 60 to 65 F — where the occupants can't get at the thermostat. Then a heat pump for each unit, with its own thermostat, and powered by that unit's electric meter (I presume they will be separate?). That way the occupants can set their own temperature on their own dime and be happy, except on the super cold days when the heat pumps can't keep up.

KEEP the steam heat, if you have a brown out, power surge or a nearby lightning strike the electronics on your mini splits will be fried, and then where will you and your tenants be????

So instead of a steam boiler that could last 30 years with very little maintenance, you want to replace it with something that will cost you $15k-$20k every 10-15 years?

I think you have it backwards. It's the new systems that require more maintenance. Steam heated by natural gas requires a very small amount of attention that any handy homeowner can give it.

For a rentalI imagine you want AC.So a ducted or mini split would be needed in addition to a steam heating system.

Or just go all FA.

I would do 2 separate units so they are paying gas and electricity, I've had pros tell me it isn't really a good idea to zone resi on different floor levels.

My mistake, but I assume you get that pricing on the steam boiler too. It's still the same problem, just with slightly different numbers.

Then yearly I would pay $350 for cleaning + $50 every month during the heating season for someone to go and drain/refill the water so it's clean.

For those who are still here, this is completely wrong. You don't drain and refill it every month and I haven't had mine cleaned in 5 years—this is gas not oil.

Not to mention steam costs more in gas per monthly than a forced hot air.

Source, please?

Thanks for listening to my ted talk and goodbye

Sounds like you had your talk all written up, not sure what you were asking for.

Mind was made up before the initial post.

@pecmsg At the cottage, often the temperature drops bellow -10F to -15F. No issues with cold climate heat pump there, plenty of heat. The outdoor unit does need to be on a taller stand to keep it out of the snow though.

@QuintonS Be careful with shared ducting between units. Most codes require some mitigation, add in the cost of zoning, you are not saving anything over 2 units.

The one issue with a furnace in a multiplex is that event the smallest one is WAY oversized for the load. A common solution here is to use a combi rated gas water tank feeding a fan coil for heat. If you need to add in AC, the BOM cost of that is still well above a heat pump only +resistance tank solution.

Can you have a system that is reasonably sized for both -15F and typical summer usage?

In heading dominated climate the unit sized for heat will always be oversized for cooling. Since you are dealing with modulating equipment, this is not an issue as long as you size reasonably well.

That commonly misquoted 140% oversize factor in man S is the MAX oversize for furnace, not the required oversize. For heat pumps it is even less, 125% MAX. Also use a proper man J without fudge factors, so if you local design temp is 0F, use 0F not -15F.

Pretty cold winters here and hot muggy summers, heat pump works well all year around. Definitely better for cooling than the typical 2x oversized single speed AC.

@EdTheHeaterMan I think the OP had his mind made up that steam is outdated and inefficient going in.