Sorry for the cross-post.  I got chastised for putting this in the wrong forum the first time:

Hello, we are in the planning stages of a new construction in Ottawa (Ontario) for a small 1600sqft bungalow.  Reading past posts, I do not see much about Hydronic Air Handlers (e.g. Lifebreath).  What are the pros and cons of a Hydronic Air Handler? Is it truly a better alternative to High Efficiency Forced-Air (Natural Gas)?  We have natural gas available and cannot afford to go with geo-exchange since we are opting to spend our limited $$ on a tighter building envelope as a top priority (ICF foundation, spray foam walls).

We have read that hydronic air is more efficient than the standard high efficiency natural gas furnace.  Both use natural gas as the heat source but the hydronic system uses the NG to heat the water which then heats the air; whereas the standard furnace uses natural gas to heat the air directly - so what makes a hydronic system superior?  It is also advertised as a good reason to go with hot water on demand since the unit is already producing hot water for air heating... is that a valid statement?  Does the story change if we also throw radiant floors into the mix?

Thanks!

Hydronic air isn't of-itself inherently more efficient than condensing NG, but there's quite a range out there- some is, some ain't.

Is the Lifebreath solution you are looking at the eKoComfort combi solution (in whichy they participated) under a different name?:

http://www.ekocomfort.ca/

A standard condensing furnace typically has 1-2 burner stages and blower speeds. With a continuously variable ECM motor and outdoor-reset control you can A: avoid temperature swings, B: run lower air velocities, which= C: better comfort at a lower temp, with less electrical power and NG fuel used. Whenver the same burner can be applied to HW heating as well the duty cycle is higher, and properly controlled, the minimum burn length longer, which reduces burner cycles and the fixed per-cycle losses that eat up efficiency when operating at well below peak load (which is 80% of the time.) If there is at least a small amount of water stored (3-5gallons) cycling losses from short water draws can be reduced, but not eliminated. A typical tankless on-demand (even condensing versions) operate at less than 50% efficiency on short draws due to excessive cycling losses, and only make it up during shower & tub draws. Combi HW/space heating systems usually beat that, and cycle the burners fewer than half the number of times.

A downside to any forced-air system is that it (unavoidably) induces pressure differences between rooms which drives outdoor air infiltration losses. In typical homes that adds up to a ~15% performance hit, more in leaky/drafty homes, but much lower in super-tight homes (tight enough to need active ventilation.) Hydronic floors/radiators/baseboard don't have that loss, and tend to perform better, when all else is equal (condensing low-temp 95% AFUE blah blah etc.).

But for new construction it's always good to ask whether spending $10 more on radiant floors to get condensing efficiency is really better than spending the same money on more/better insulation and lowering the heat load, and using high efficiency hot air, or even cheaper systems? The PassivHaus approach has it's merit- built it superinsulated & super tight, heat it with a 1-2 kilowatt heating element in the (necessary 'cuz it's so tight) ventilation air stream.

It doesn't take a superinsulated house to reach the point where the peak hot water load (when taking showers) exceeds the design-day heat load by a factor of two or more. When that happens combined systems have some synergy that can add up to better efficiency for both, if it's done right.

We did this on our house because we have a water to water heat pump and a boiler for backup. You're gonna find it's not very common to use a hydronic air handler and they're difficult to find ones that both heat and cool. We finally found one, probably about the only one available from a company called FirstCo. It's a nice unit, and not too terribly expensive, and it works well. Controls are a little funky, but nothing unmanageable. It's a variable flow unit, 2-3 speeds.