To answer this question, if helps to first understand how your body reacts to a room environment and how you know when you're comfortable.
A common misconception is that the way
to make your home comfortable is to provide enough heat to keep your
body warm. In fact, your body loses heat to its surroundings and the
rate of that heat loss is what makes us comfortable – or not. You
may remember from science class that heat always travels to cold
because the environment is always trying to achieve thermal balance.
Your body reacts the same way to its environment – giving off heat
to the surrounding air and surfaces. The rate at which your body
gives off that heat determines your comfort level. The slower your
body gives up its heat, the more comfortable you feel. The job of
your heating system is to slow the body's rate of heat lost to the
environment.
Your body loses heat four ways:
- Radiation (heat lost to cooler surfaces in the room)
- Convection (heat lost to the air around you)
- Conduction (direct contact with cooler surfaces)
- Evaporation (from your skin)
About half of this lost body heat is
through radiation, with another third through convection, and smaller
amounts to conduction and evaporation.
Of these four, a hydronic heating
system uses radiation as a large component of its heat-delivery
method – which means it heats the objects in the room rather than
just the air. Your body senses these warmer surfaces and gives off
less heat to them. A forced air furnace delivers warm air to the room
and heats the room surfaces through conduction, resulting in cooler
surfaces and a less comfortable environment.
A hydronic system also delivers heat
through convection. This creates a gentle, natural air flow as cooler
room air flows across the radiator and is warmed by conduction. This
air flow is imperceptible to your body but acts like a blanket of
warmth. By contrast, a forced air furnace creates air flow using a
blower, causing a cooling effect when that air contacts your skin.
It's the same feeling you get when standing outside on a sunny but
breezy day. The thermometer may indicate that the air temperature is
warm, but the sensation on your body is that it's cooler.
Because the surfaces in a hydronically
heated room are warmer to the touch, you lose less body heat and feel
more comfortable when you touch other things or surfaces in the room.
A great example is a radiantly heated floor. Your feet lose no heat
to the floor, so your body feels more comfortable – even at a lower
room air temperature. A conventional, forced air heated room will
often have a “comfortable” air temperature but you'll feel cold
because your feet are in contact with a floor that is several degrees
cooler than the air, and much cooler than your body.
The last way your body loses heat is
through evaporation. Your skin cools as its moisture is lost to the
surrounding air. A hydronic heating system doesn't dry out the air as
a forced air system will. This reduces the evaporative effect on your
skin and leaves you feeling more comfortable.
When it comes to comfort, hydronic heat
offers clear advantages over forced air.
Next week I'll discuss how hydronic
heating systems are more efficient than forced air.
Heidronically yours,
Wayne
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