Insulating under baseboard registers


Old 04-11-03, 04:57 AM
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Question Insulating under baseboard registers

What's the best way to insulate under baseboard registers for hot water heating There is quite a draft coming in from outside.
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Old 04-12-03, 08:01 AM
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Volume of air in house remains constant.

In other words, air cannot come into the house without the same volume of air leaving the house. Furthermore, whenever you heat air, it expands. This pushes air in the house out of the house. When this heated air cools, it contracts. This draws air from outside to keep the volume of the air in the house constant. This is your primary source of air exchange in the house during the winter and how humidity is removed from the house.

Hot water heating gives the illusion that air is infiltrating the home, when in fact it is a process of heat transfer known as convection. The heating element, usually a copper tube with aluminum fins, gets warm as a result of warm water being pumped through the copper tube. This in turn heats up the air surrounding the heating element. as this air is heated, it rises. This draws air at the floor level towards the heating element to replace the heated air leaving the area around the heating element. This is known as convective heat transfer. The cold air at the floor being drawn to the heating element gives the illusion that air is infiltrating the home in that area.

People say the same thing with forced air systems about cold air returns. They complain that these vents are blowing cold air, when in fact they are drawing cold air into the system to be heated. To visually see what is occuring, put a smoke stick near the bottom of the baseboard while the system is on and you'll see the smoke go into the baseboard at the bottom and come out the top. This principle of volume of air remaining constant applies to everything throughout the house, regardless if it is air leaving the house, the volume of heated that comes out of the top of your baseboard must equal the volume of air that goes into the bottom of the baseboard, to the volume of air that comes out of heat vents equals the amount of air going into your return vents, etc.

Air infiltration (low pressure) equals air leakage (high pressure). Though it is unlikely that the cold air you feel at the bottom of your baseboards is air infiltration, let's assume that it is. If we apply this principle to your situation, then the same volume of air coming in at the baseboards must be leaving he house. During the winter the air infiltrating (low pressure) the home is cold air. Air leakage (high pressure) from the home is warm air. To illustrate the amount of force involved here is if you could let either air into or out of the house without air leaving or replacing the air, your ears would pop just like in an airplane. The same effect with your ears would occur when the air is heated and expands and then cools and contracts, if the air was not allowed to escape and be drawn into the home.

There are many in the air sealing and building performance industries, including many of my collegues, who argue that by prohibiting the amount of air into the home,you prohibit the amount of air leaving the home. I disagree and stand fast on my position that only high pressure areas should be air sealed. I base this on two premises, one is it is heated air leaving the home (high pressure) and the second is the force involved to keep the volume of air constant in the home.

In other words, if the was air infiltration at the baseboards, which I doubt, I would give it very little attention and only view it as an indication that the same volume of heated air is leaving the home somewhere else in the home. It is the air leakage (high pressure areas) I would air seal in the home.
Old 04-12-03, 08:13 AM
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Thank you for your reply. Your explanation does make sense. I just don't want to be heating the outside nor over - heating to compensate for a space that could be better insulated.
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