Efficient home heating, Part 1.

Nighttime lows have been dipping into the twenties, making my cozy little home all the more comfortable.  The Armstrong House, the physical structure that protects me from the raw forces of nature, envelopes me in a bubble of evenly warmed air.  The source of this warmth: underfloor – or radiant – heating. Although winter is a great excuse to wear indoor slippers, they are not much needed as my floors radiate a steady stream of thermal energy.  On those early mornings when my cat's demands for breakfast rip me from the bed, my toes happily waltz naked across the heated floor.

Walking on heated floors is a delight in the Armstrong House

A little background on the Armstrong House 
When the Pound Ridge Land Conservancy (PRLC) committed to renovating the Armstrong House, they decided to use it as a showcase for simple energy efficient building and lifestyle choices.  The PRLC chose to prioritize energy efficiency because it realized that both prongs of conservation (land protection and sustainable lifestyles) need to be practiced and taught.  At the Armstrong Education Center we call this philosophy 'Living Lighter on the Land', and radiant heating is just one of the many ways we demonstrate a low-impact lifestyle.   

How radiant heating warms the Armstrong House
Like the tortoise, radiant heating (AKA, underfloor heating) is slow and steady.  There are many different radiant systems available – air, electric and water – which differ in their heat-carrying medium.  At the Armstrong House we use water (AKA, 'hydronic') to carry heat throughout the house.  Here is how our system works: roughly 90 degree water is continually pumped throughout the house in underfloor plastic 'PEX' tubes.  The water's heat energy leaves the tubes and radiates upward into the cooler room. Radiant heating systems can be thermostatically controlled, just like other home heating systems.  Take a look at the pictures below to understand the basic design of this heating system.

Underfloor tubing runs throughout the entire Armstrong House like in this picture.  

A picture of plastic 'PEX' tubing in a room.  This tubing will be covered by a floor.  

A detailed look at how radiant tubing sits under a floor.  

Radiant heating versus other types of heating
What makes radiant heating so efficient and great feeling is its omnipresence – the tubing underlies nearly all of a room's floor, which means that heat enters the room from almost every inch of ground.  Alternatively, radiators and forced-air systems rely on a few sources of very hot air, which is expected to permeate a space.  The result with these systems are drafts, hot pockets, cool pockets and – as you'll see – a room that is heated from the top down.

Two systems of heating compared.  Forced-air systems on the left and radiant floor systems on the right.  In most cases, radiant heating is more efficient and comfortable.  

Radiant heating literally heats a room from the bottom up, which means that the space occupied by people (the bottom six feet of the room) is the warmest and most comfortable.  Alternatively, by heating a room in a top-down manner (as in a forced air system), energy is wasted heating unused air.  This also creates very dramatic and noticeable differences in heat conditions between floors.  For example, I remember in my grandmother's house the second floor was brutally hot while the first floor was comfortable.  Besides being uncomfortable, this style of heating is inefficient.    

Comparing how heat fills a room in different heating systems.  Radiant heating on the left vs. force-air heating on the right.  

The body's response to different heating systems
It is said that radiant heating has advantages over other heating systems on a purely physiological level.  When looking at the heating preferences of the human body, our feet and legs like to be the warmest and our heads like to be the coolest.  The diagram below reiterates the point that a bottom up heating system has advantages over a top down heating system.

Our bodies like to be heated from the bottom up.  Our heads like to experience slightly cooler temperatures than our legs and feet.  

When trying to reduce your energy and resource use, you have to tackle the large energy hogs, like home heating.  Here in the north, many months are spent heating the home and an efficient system will make a large difference over time.  This post is Part one of a series on efficient home heating.  In part two I will show you how the water in our radiant system is heated.  Here's a hint:  Its big, yellow and likes to sit in the sky.  Stay tuned.      

More reading

There are lots of people talking/blogging about radiant heating technology.  It is found all across the country and applied in all sorts of buildings.  Here are some links.  Happy heating!

From the Federal Government

Wikipedia

A Hudson Valley-based private company specializing in radiant heating

A Vermont-based private company specializing in radiant heating

Lots of good radiant information here