What are the advantages and disadvantages of forced air heat, vs. hot water, vs. steam?

With forced air, you can install ducts of sufficient size so that they can share cooling duty in the Summer, but some people find them drafty. I think circulating hot water is easier to plumb because you don’t need a two-pipe system (no return for the condensate is necessary.)

The main thing is to install a very efficient furnace, and to insulate properly.

I can’t answer definitively, because within those broad categories there’s still room for a lot of variation in the system that can overcome some of the disadvantages of any one, but…

Forced hot air systems are often drafty, involve a lot of relatively bulky ductwork (meaning it can be difficult to add a room, for example) that will eventually accumulate dust and other things that you won’t want to have blowing on you, and can be especially dry in winter, since you’re blowing hot, dry air into a room that is naturally drier (usually) just because of the season. On the other hand, as @pdworkin said, these are easy to adapt to cooling in the summer, too.

Hot water involves plumbing and radiators that are permanently filled with water (unless you go to the trouble of draining them, or there’s a break), so that means that you cannot afford to have a long-term power outage / heat loss, or your heating system will freeze, and then it will break and it will cause very extensive structural damage, and ruin most of your carpets and furnishings. Otherwise, it’s a relatively benign system that produces fairly steady heat from well-placed radiators. It’s also a bear if you live in an older house with, say, ½” copper tubing—even with an adequate and efficient furnace, you may not have the plumbing capacity to heat the space you need to.

Steam is one form of residential heating that I have no experience with (which is kind of ironic, considering that I work for a steam boiler manufacturer—but we make large power boilers for the electric utility industry, not heating boilers, and no kind of “residential” work).

You forgot to mention radiant & convective heating from electric elements, which is very nice: steady, well regulated, fairly easy to expand—but expensive. Other forms of radiant / convective heat, of course, include wood stoves and the like.

Personally, if I were building a new home or planning to move I’d be looking into geothermal / heat pump for a closed glycol / hot water system (very resistant to freezing), and passive solar.

@CyanoticWasp – Thanks! I left out electric heat because heating by electric these days is ridiculously expensive – there’s no way I can imagine anyone even considering it for any reason (until the day comes that we all have LENR/Cold Fusion reactors in our basements – which might not be that far off). The reason I ask is because I recently bought an older house that has a hot water system. Before that, I’ve always had forced air, and have never considered anything else. But I kind’a “fell into” this house due to recent circumstances. Despite the fact that it’s an older poorly insulated house, I’ve noticed that the hot water is very efficient, my heating bills are comparatively less than with hot air, and the house is heated more evenly and the temperature more steady during the day (I was wondering if anyone would mention the lower cost of operating a hot water system for the same comfort level). Though I miss being in a newer house with central air.

Hot water is great as long as you never run out of fuel when it’s below freezing. Also, be sure to bleed the units.

I had it serviced before the heating season, and plan to every year. So I trust that the mechanic will do whatever’s necessary like that…

@HungryGuy Hot water systems (oil-fueled furnaces) are pretty much the norm in New England, since so many houses here were built before the gas infrastructure was installed. (LP gas is also fairly common in more rural areas.)

I’ve had hot water systems (as a child in my parents’ house) and now as an adult for most of my life. Routine servicing of the furnace is important—for any furnace—but I never do a thing with the circulating system itself; never have to. The worst problem I had was a leak at the oil tank outlet to the fuel feed line. That spilled several gallons of fuel oil onto the cellar floor before I noticed the smell and tracked it down. That smell lasted for months, and ruined some carpeting in the next (finished) room next to the oil tank.