Difference between Forced Air Heating & In-Wall Gas Heaters?

You can't

install a gas heater in a bedroom

Hot drinks are for warm feelings

Forced air delivers warmth by blowing air heated to some practical level. It is usually low to very low temperature air which allows for huge gas flue condensation at the furnace. Such modern equipment comes with fantastic efficiency numbers on the yellow label that tell us the warm air furnace portion of the heating system seemingly trumps any other boiler schemes we can think of for our homes. Forced air heat is delivered into the rooms as nothing else but pure convective warmth, the radiant heat component is lost somewhere along the line. Lost, as in lost efficiencies.

Now, if your home is draughty and either your supply or return ducts are built with lots of hair crack leaks (which applies almost always) you'll find yourself spilling away of lot of your expensive air. Delivery ducts, because they 1) handle so much volume and 2) because they are so large in surface are a big huge source of lost heating efficiencies.

In the world of heat transfer, the radiant mode is the one that packs all the bonus points for power, mainly because it sides with a powerful mathematical concept: heat radiation relies on not just the square, not just the cube, but yes the fourth power of the temperature heat jump between objects in the room and the heating media. Both conduction and convection live in bliss ignorance of this power concept.

How do we maximize this radiant power to the great benefit of system wide heating efficiencies? Simple, bump up the temperature differential between the radiators and us. Opportunities for radiant heat transfer dwindle real quick when we reach for ambiguously low temperature heating media (remember, the fourth power of a tiny amount is still a tiny amount compared to how huge everything gets as we start with bigger and bigger numbers, play with the adding machine, you'll see: 1 [yX] 4 = 1; 20 [yX] 4 = 160,000; 120 [yX] = 210,000,000)

There are many practical ways of getting some heat delivery by radiant mode. Preferentially the radiation kicks in as we go hotter and hotter with the heating device inside the room. A central forced air grille delivers near zero radiation. A low temperature water convector starts delivering the stuff but still in very low dose. So called radiant floors actually deliver very little radiation, but since there is so much floor surface to play on, what is prescribed at homeopathic dosage turns out to have a very nice curative effect. Next, steam radiators start packing major loads of efficient radiant heat transfer, just because the gadgets are hot. Electric ceilings work a bit like the broilers and the hot lamps that used to be so popular in the motel rooms deliver heat that compete with the good feel and efficiency of the sun.

Wood stoves, radiant gas tubes, and some of the wall furnaces fall anywhere in that spectrum depending on how close you are exposed to hot flame and hot flue surfaces. Obviously, the cozy hot cocoa feel we seek at the ski lodge is the one of the metal wood stove, and some of the gas fired wall furnace, and the simulated fire places. Not bad stuff.

OK, who I am kidding? who drinks cocoa straight? The purpose of central heating, be it central air or a hydronic boiler adds the practicality of having efficiencies of scale: for instance, one big boiler with one pilot light trumps the dozens of heating units each with their own pilot. Construction details make big unit efficiency more possible than in tiny equipment - small is not beautiful. Also, and more importantly, small live fired units scattered around our living space bring in all the dangers of CO poisoning, gas leaks and fire hazards and in that regard, both hydronic versions of either hot water or steam come with the possible safety enhancements of a separate boiler room.

Do I like wall stoves vented to the outdoors? yes. More than one or two inside a real home and you're better off with boilers and radiators. Lastly in my book, the unvented simulated open flame gas fire log is a big NO NO.

The wall furnace has got to be one of the better choices for heating a small ski lodge.

Too much help here... or too much words?