Go With the Flow – the Energy Flow

Within homes, we direct the flow of energy to produce hot water, to heat or cool spaces and to exhaust air.

In a hydronic boiler (Illustration 1 H069C), a flame heats the water in the heat exchanger. The energy circulates through radiators or convectors. The system might have zone valves or multiple circulators to direct heat into certain zones.

Not all the energy goes into the water. In some systems, as much as 35% of the energy goes up the chimney with the products of combustion. Although this may seem wasteful, that energy keeps the products of combustion warm, so they flow up the chimney without backdrafting.

Energy going up the chimney also keeps the products of combustion above the dew point, which is approximately 130°F for natural gas combustion. And keeping the products of combustion at approximately 140° prevents condensation on the heat exchanger.

That’s fine, but sometimes, energy goes astray.

Ice dams point to problems
Ice dams indicate an energy-flow problem (Illustration 2 I022C). In cold climates, heat pushes warm air into the attic through any little opening. Leaks at “can” lights make this worse because the can fixtures create additional heat. Insulation contact (IC) fixtures leak air, but they have a thermal trip switch to prevent overheating. Insulation contact air-sealed (ICAS) fixtures also leak air.

Problems with bathroom fans
Dripping bath fans indicate another problem with energy flow (Illustration 3 V007C). Both the bath fan’s pressure-activated damper and the damper in the roof vent connector can get stuck in the open position. Often, ductwork in the cold attic is not insulated. Warm, moist air condenses in these areas, creating leaks around the bath fan.

Here’s a basic principle to remember: As energy creates movement and changes vapor pressure, condensation occurs. That’s your clue to where the energy goes.