In North America, most homes are heated by forced air. It seems like a good idea; you get to use the same system of ducts to heat and cool; it responds really quickly when you adjust the thermostat; you can add filters and humidifiers and other stuff to it. They are not like that old octopus system that ran on coal and convection; now you can get high tech accessories like Nest Thermostats and smart vents that give you more control than ever. It’s the standard go-to solution.

But there are other options that can keep you warm and toasty, such as radiant floors and hot water radiators. However before you can discuss which system is best, one has to understand what makes you comfortable and feel warm in the first place. And it’s not what most people think. (And this is not a discussion about the source of heat; that could be gas, electricity or a heat pump. This is a discussion about the delivery system.)

The single most important bit of science about feeling comfortable is that it has little to do with the temperature of the air; as engineer Robert Bean notes, it's not about the heat you are absorbing, it is the heat you are not losing, which results in perceptions of comfort. (See more on this topic in the post There's more to comfort than just picking a furnace or an air conditioner.) So your Nest could be telling the furnace to pump out 74-degree air, but if you're standing by a big window, you will be losing body heat to that cold surface.

That’s why the single most important feature of a home’s heating system is the insulation in the walls and the quality and quantity of the windows, If the walls are cold and the windows huge, you are not going to be comfortable no matter what the heating system is. Then there are other factors that affect comfort too, including humidity, air movement, clothing, activity and state of mind. But we are all fixed on temperature, because it’s easy. As a British government agency notes,

The most commonly used indicator of thermal comfort is air temperature – it is easy to use and most people can relate to it. But although it is an important indicator to take into account, air temperature alone is neither a valid nor an accurate indicator of thermal comfort or thermal stress.

So understanding that, let’s look again at that forced air system that almost everyone has. First of all, in many American systems, the ducts run in the attic and in many cases, they are leaking like mad. Then the vents are often located under windows, to counteract the downdraft that comes from older windows with lots of heat loss. That's a fine idea, but the ducts get long and bendy. The systems are often difficult to balance, the return air handling can be different from room to room. And the vents are usually not in the right place for cooling, where you want them high instead of low. There is also the issue of fan noise and room to room noise through all the ducts, dust and pollen moving around, lots of air movement that can be annoying.

Finally, there is the problem of combining ventilation with heating. Ventilation is the controlled management of fresh air, and you really want that all the time, not just when the furnace is running. It would be nice if it was all handled by sucking air out of smelly bathrooms and replacing that with fresh air somewhere else. This isn’t a lot of air, a lot less than you need to supply for heating.


radiatorRadiator built into bookcase, where it doesn't work very well. (Photo: Lloyd Alter)

In Europe, people are used to radiators, which came first because people who own houses in Europe expect to live in them for generations. So when central heating became popular it was retrofitted into existing houses, as it is a lot easier to squeeze a pipe in existing space than a duct, which needs all kinds of boxing and bulkheads. Hot water heating also didn't need electricity, as the water would circulate by convection. This worked very nicely in taller multi-floor houses and flats since the lines had to run vertically; it was not until circulating pumps came along that one could design a more horizontal system and do more complicated retrofits. However people got used to systems that are totally silent, and do not move dust, noise and smoke through the ducts. Even in new builds, they continue to prefer radiators to forced air.

radiatorToasty towels on my radiator. (Photo: Lloyd Alter)

There many different styles of radiators, tiny little very efficient furnaces, sophisticated valve systems to balance it all, and people have to dust their houses far less often because the heating system isn’t moving all the air around. Bathroom radiators double as towel warmers and are very cozy.

Radiators were usually placed under the windows for the same reason that vents are- old windows are huge heat holes that cause significant drafts, and the rising heat from the radiators counteracts the drafts. But with a properly insulated house with good windows, they really can go anywhere.

Radiant floors


Radiant heating is hot these days, and is almost always marketed with puppies and people lying on the floor. It’s also controversial; writing in TreeHugger I have been critical of it because of what’s called thermal lag, the long time it takes to respond. Alex Wilson, author of Your Green Home, has written:

“it’s a great heating option for a poorly designed house…. For the radiant floor system to provide enough heat to feel warm underfoot (the feature everybody likes with this system) its going to be cranking out more heat than the well insulated house can use, and it will likely cause overheating. A radiant floor heating system also has a very long lag time between when the heat is supplied to the floor and when the slab begins radiating heat….If there is a component of passive solar heating in the home, it will cause overheating because you can’t turn off the slab when the sun comes out.”

This turns out to be not exactly true in a properly designed and controlled system. Robert Bean counters:

Overheating in all buildings occurs with various combinations of enclosure performance, building mass, solar control, control over internal loads and control over the heating systems (and all types of systems not just radiant). Poor control over one or more of these elements can prevent the occupants from shedding their internal body heat at a rate fast enough to feel comfortable.

The main problems with radiant heating come from the fact that it is so oversold with so much misinformation. Energy savings of 30 to 50 percent are promised, often claiming that because you feel warmer, you set the thermostat lower; it may be true for some but not everyone. It does not “save energy”. In fact, Robert Bean has pages and pages of myths which he happily discounts. (If you want to get totally lost down this rabbit hole, check out Bean’s website, Healthy Heating.)

radiant flooringMy, radiant flooring sure does look complicated. (Photo: Wikipedia)

Radiant in-floor heating is more expensive than other systems, with all that tubing and the systems that hold it in place, but once again we have the granite counter syndrome- people will happily spend tons of dough on things that you can see but argue over every nickel going into insulation. They would much rather spend a few hundred bucks on a so-called smart thermostat that promises savings than they would on things like better windows that actually deliver it. But everyone I talk to who has put in a radiant floor system loves it. I regret not having put some into the slab in my house when I renovated last year.

In the end, the best heating system is almost no heating system at all, and recognizing that when it comes to comfort, the house itself is the most important element of the heating system. After all, the heating system’s function is to compensate for heat loss through the walls and windows when it is cold out; if there is almost no heat loss, then you need almost no heat. That’s why so many Passive and super-insulated houses get by with little mini-split heat pumps; they only need a bit of heat or cooling to be comfortable all year round. Because the most important lesson in all of this is that the house design matters a whole lot more than the heating system; all of the delivery options have their virtues and problems, but the best option is to barely need one at all.
