I agree with Mike about adding a nat gas forced air furnace system. you probably will need ductwork modifications. I would add a small supply and return to basement area...what is your location?...I don't understand why a boiler would be considered....your location please...ductwork to basement should be more practical and less expensive than a mini split.

IMO

We are in Metro Boston area. So a hydrocoil system wouldn't be efficient for my climate? Our basement is half below ground, half above. We were just going to leave the electric baseboards, but someone suggested it may be more efficient for the mini-splits, but obviously if we are able, ductwork would be the best route. For whatever reason we can't get duct work in the basement, should we just leave the electric baseboard?

Hydrocoil systems are not common and expensive. I am no experience with them, but I would think they would be less efficient than a furnace that is is rated 95%+ efficiency.

A mini split would cost less to operate than electric baseboard. However it will cost you $7-10K for a mini split installation. You may never recover that initial cost. I suggest leaving the electric baseboard in the basement since the heating load is small. If you could add a furnace vent or two then you could use the electric baseboard as a supplement on very cold nights and keep the operating costs low.

Where is your current A/C system and ducts located? If its in the basement (and works well) I would recommend replacing it with a new unit that provides both gas heat and A/C. If its in the attic, you may not be satisfied with just adding the heat capability, since it will be hard to force the hot air downward in the winter, and the top floor will always be much warmer.

I also agree that its easiest to leave the baseboard heat in the basement, and you probably don't need A/C there if its mostly below ground. However, having A/C ducts there would help with dehumidifying the basement, which is often a concern.

Bruce

Matching new and
newfangled systems to existing homes can be very challenging. All electric homes were typically very well
insulated but even that might not be up to today’s standards. Have there been improvements in air sealing
and insulation since the home was built?

I can see why the
hydronic coil might be useful. You don’t have room for a furnace where the
existing air handler is, and the the duct system can’t be made to work with a
furnace in the basement. There are a couple of problems to consider with the
hydrocoil idea. To have a large capacity, hydrocoils need to be big or run hot,
your choice. Since you don’t have room
for a furnace with the existing AHU, you might not have room for a big
hydrocoil either. You might be able to ameliorate this somewhat with more than
one coil in the ductwork if it can be fit.
Ok what is the problem with a hot hydrocoil? That seems logical after all. It has to be hot to provide heat, right? It boils down to physics if you'll forgive the cheap humor. For anywhere near efficient boiler operation,
you need your return water to be below 130 F.
Even lower, much lower, is better.

Hot water-driven
convectors (aluminum fin baseboards) also need relatively hot water, but not
nearly as hot as a typical hydrocoil in an AHU. Toe-kick heaters are
hydrocoils. Radiant floor heat can use
very low temp water and are a good match for condensing boilers. Cast iron radiators are pretty good too,
falling between the convectors and radiant floor heat. You can run them all from one boiler as well
as domestic hot water (and melt the snow on your driveway if you want) and it
can all be done with upwards of 95% combustion efficiency with skillful
design. That is easy with a new
building, but you have to be somewhat lucky with an existing home. You also have to know a lot of stuff yourself
or have a very good installer. With a
boiler in the basement, you could run the hydrocoil and install baseboard close
by in the basement in a separate zone. My only caveat there is that small zones can be a problem
without a buffer to keep the boiler from short cycling.

Maybe efficiency of
the boiler is not your top concern.
After all, you are going from electricity as fuel to nat gas. The
difference between boilers burning at 82 and 98% might not be a big deal. Just don’t let someone install a high
efficiency boiler that can’t take advantage of that design because you can’t both run it at low water temps and keep your house warm. It won’t work very well. Note that in less than the coldest weather if
the system is set up right, you can still run in an efficient mode with lower water
temps, just not for as much of the time.
If a modulating/condensing boiler is dropped into a system where it is
snapping on and off a lot and can’t condense, it will be neither efficient nor
last long. They are not built for that
and since they cost more, even a bigger waste of money right from the start.

Here are some considerations for boiler chic if you go that route.

Don’t settle for a combi boiler providing both heat and
domestic hot water directly without a lot of proof that it will work well for
you. They are difficult to fit to heating and hot water needs in houses, but
might work better in apartments and condos. An indirect tank on a
different boiler might be a much better choice.

There is a company very local to you
makes a system that is might often be a best match to existing hydro systems
and don’t require the sophisticated engineering that some other condensing
boilers do. It might work well for you. The HTP Versahydro and
Versaflame boilers look like a very good idea. The primary heat exchanger
appears to take advantage of the natural polarization of hot water in the tank.
The buffer is built in. If your demand is low, you might substitute a
Westinghouse Stainless SteelGas-FiredWater Heater. They are either
licenced or built by HTP and have a 1:3 turndown ratio vs. 1:5 for the Versa
boilers. They won’t do domestic hot water unless your installer adds a
secondary heat exchanger (and indirect tank). It could be a very cost-effective
solution, and is more forgiving of less than optimal system design, like the
HTP Versas, due to its buffering capacity.

Finally, for hydronic heat and boilers, there are a couple
of boards that I know of that have a lot of generous and knowledgeable
posters. One is Terrylove.com (DIY forums) and the other is
heatinghelp.com.

I don't see the benefit of spending all the additional money on a boiler for a hydrocoil system versus a forced hot air system. From a financial and efficiency perspective the forced hot air system is the better choice in my opinion.

RE: mike_home

“I don't see the benefit of spending all the additional
money on a boiler for a hydrocoil system versus a forced hot air system. From a
financial and efficiency perspective the forced hot air system is the better
choice in my opinion.”

The short answer is that every situation is different and
unique. Hybrid systems might also be considered to either rule in or out in any
given situation, particularly where hydronics already exist.

“A given volume of water can absorb almost 3500 times a much
heat as the same volume of air, when both undergo the same temperature change.”

Therein lies the potential efficiency gain. Whereas forced
air requires large ducts and high wattage blower motors to circulate air,
water, for the same Btu transfer, requires small diameter piping and much
lower wattage circulators. Hydronic systems can also be easier to zone, also
increasing efficiencies.

Hydronics can be quieter, create less draft and may
contribute to greater open usable space when embedded within the floor.

Of course all HVAC ‘Systems’ require proper design,
installation and control management to deliver comfort and efficiency.

IMPO

SR

fsq4cw,

Maybe I am misunderstanding what the OP means when he refers to a hydrocoil system. I think it means hot water boiler connected to a coil which a blower forces past on its way to be distributed thorough a system of ducts.

However if we are talking about a hot water boiler connected to baseboard radiators, then I agree with you that overall would be more efficient and comfortable.

Hi Mike,

I think you have it right. My post was just a general
statement. We can’t really say what the OP should do as we’re not there. We can
only suggest avenues to explore.

SR

I don't have installation costs or operating costs.

I don't know if a furnace in the current position of the air handler is practical. I don't know if ducts from a basement furnace is practical. If the answers to the location questions are no, what to do?: is hydrocoil the only choice? How about high velocity? Can't say that I have not heard much about that recently.

The OP needs to return and provide more details of the current location of the equipment and how it is connected to the existing duct work.