Transformers are not wonderfully efficient, but ohmic losses at low voltage can be devastating. If a device only requires a quarter watt, ohmic losses at 12 volts wouldn't be much of a problem, but even a 50% efficient transformer wouldn't waste much energy. Products that require real power, however, are another story.
Consider a product which requires 112 watts, is located 100 feet from the power supply, and is connected to a 12-volt supply with #6AWG cable (that's like booster-cable wire!). Such cable has a resistance of about 0.0004 ohms/foot, so the total resistance would be 0.08 ohms. With 10 amps flowing through it (as would be the case with a 112-watt load) the wire drops 0.8 volts. Despite the large cable, over 8 watts gets wasted in the wire!
Now consider a 119.75-watt device powered 100 feet away from a 120-volt source. Such a device may be powered with over 98% efficiency using 18-gauge wire (0.0063 ohms/foot, or 1.25 ohms total). The wire would drop 1.25 volts, wasting only 1.25 watts.
As a couple of additional points of comparision, using #6 cable would result in less than 100mW of loss; if 5% loss were acceptable, 24-gauge wire would suffice.
Try this alternative.
Don't use electricity for these devices, use Natural gas.
High efficiency Gas Furnaces are rated in the 90% to 98% efficiency rating nowadays.
Much more efficient than any electric furnace.