Can Running the HVAC Fan Continuously Save Energy? (Part 2 of 3)

Not all blower motors are designed for ON mode!

Check if the fan is rated for continuous use.  If your fan isn’t rated for continuous use but you still elect to run the fan in ON mode, budget to replace the fan sooner than normal with a fan that is designed for continuous use.

Other Issues

  • Filter gets dirty faster, system works harder.

Remember the filter we discussed in Part 1? The filter clogs up more quickly if you run the fan continuously. A clogged filter makes the blower motor work harder and uses more electricity. If you run the fan in the ON mode, change your filter every month.

  • Unconditioned air is always in the loop.

If supply ducts are in the attic or crawl space, unconditioned air will circulate into the home all year round, which may cause the system to cool or heat more frequently.

  • Humidity increases, moisture is introduced into the house.

During the cooling season in humid climates, running the fan in the ON mode can actually increase humidity inside your home, which introduces moisture into the house.

  • Environmental issue

Last but not least, there also is an environmental issue...see Part Tres of Three!

by Mark Munsch

Combustion Air: What Is It? Why Is It Important?

A recent fast moving snowstorm expected to bring heavy accumulation of snowfall had XCEL Energy (natural gas supplier) warning radio listeners of making sure exterior vents were not blocked by snow buildup.  Xcel's concern, obviously, was a safety issue that if venting was not properly maintained, indoor carbon monoxide levels may increase due to inadequate combustion and venting of gases.

All fossil fuel burning appliances need ample air intake and draft to complete the combustion process in a safe and efficient manner.  The most common fossil fuel heating systems we see in Colorado are forced air furnaces fueled by natural gas.  Some homes have multiple furnaces and water heaters all requiring ample amounts of combustion air.  Whether one or multiple, including gas boilers, the same rules apply.

So, what is combustion air?  According to the Housing Industry Research Center, the definition is as follows:  (http://hisearch.org/C.aspx)

Combustion Air - (1) Air that is supplied to combustion appliances to be used in the combustion of fuels and the process of venting combustion gases.  Inadequate combustion air can lead to dangerous problems.  (2) The duct work installed to bring fresh, outside air to the furnace and/or hot water heater.  Normally 2 separate supplies of air are brought in: one high (for ventilation) and one low (for combustion).

Depending on the year of construction and the style of the dwelling, there are several ways in which combustion air is provided to the home.  This can be through crawlspace vents for crawlspace appliances, exterior wall vents that allow for air supply through metal ducting for basement and main levels, or simply roof, gable, and soffit vents for attic installations.

What Xcel Energy didn't mention specifically, but implied in it's warning to consumers, is exterior vents are also commonly obstructed with leaves, plastic bags, bird's nests and lint.  Frequently, interior vents have been blocked with sweatshirts, towels, and rags by the homeowner because of the "cold" coming into an otherwise comfortable living space.

Please take a moment and locate the vents that supply your gas appliances making sure they are freely open, unobstructed, and able to do the job they were designed to do.

by Mark Munsch

Can Running the HVAC Fan Continuously Save Energy? (Part 1 of 3)

Question

"What's more energy efficient - ON or AUTO?

I leave my fan on to keep air circulating but I've heard lots of different answers, including 'The AC pulls in air from the outside,' but I don't think that happens unless a door is open. The other answer I've heard is that 'It costs just as much to run the fan on as it does when the AC is also running,' but I thought fans require low power so that doesn't seem to make sense to me, either."

Answer

Let's start by making sure we're on the same page with regards to definitions:

  • AUTO mode = Fan is on only when heat or AC is triggered by the thermostat setting
  • ON mode = Fan is on all the time

Let's also assume we're talking about a central air system with a blower motor (fan) located inside the home. These systems are usually "closed loop systems," which circulate conditioned air (heat or AC) throughout the home via ductwork and vents in the floor, walls and ceilings. There typically also are larger vents, usually one per floor, which collect and return air back to the fan to be reconditioned and distributed throughout the home. The system usually includes a filter in the loop, typically in the air handler where the fan is located; the filter cleans air before it is recycled.

There are two types of fans - AC and DC voltage. AC fans are more prevalent, so let's use that as our example; let's also ignore efficiency and power factors because they're immaterial.

Warning, math required!

A typical AC fan motor uses about 500 watts when it's running. Therefore, if you run the fan continuously for a 30-day month (720 hours), you would use 360,000 watt hours (720 x 500) or 360 kilowatt hours (kWh). Therefore, the fan uses about 360 kWh per month in the ON mode. The average kWh in the US costs about $0.12 so it costs about $43 per month, or about $520 per year, to run a fan continuously.

At this point, it should be pretty obvious that AUTO costs less than ON but let's math it out to its logical conclusion.  If we assume an average of 10 hours on and 14 hours off per day, energy costs are reduced by 60% to about $18 per month or $215 per year.

Bottom line - If you run the fan in AUTO mode, you'll save about $300 per year.

If you do want to run the fan continuously, there are a few important things you'll need to consider...

...see Part Deux of Three!

by Mark Munsch

Water Heater Temperature Pressure Relief Valve (TPRV)

Technical is a topic used to provide more information on terms commonly seen in US Inspect reports.

TPRV stands for Temperature Pressure Relief Valve. The TPRV is a valve on the water heater that will release water if excess pressure is built up within the appliance. Because the water released from the TPRV is very hot, it must be contained and discharged to a safe location by means of the pipe extension.

A TPRV can be found on all new water heaters. It is located either at the side or on top of the unit and can be recognized by the small operating lever. Just behind the lever is a flat metal ring on which is stamped the TPRV pressure and temperature ratings. Most valves are designed to discharge at 150F degrees and/or 210 pounds per square inch (psi). The TPR valves should be tested regularly to insure proper operation.

Because of the high pressure and temperature involved in a TPRV discharge, only certain materials can be used as a pipe extension. Standard PVC piping is not approved since it would not hold up to the temperature or pressure. CPVC has been tested and found capable of withstanding prolonged bursts from a water heater TPRV.

Smooth-walled copper, iron, and galvanized steel pipes are the materials recommended for pipe extensions. Corrugated piping can create turbulence within the pipe, which prevents pressure dispersion and increases the possibility of pipe rupture. Flexible piping is prone to crimping, which can have the same effect. Pipe extensions should be terminated within 6 inches of the floor, assuming that the water heater is located in an area where the floor will not be damaged by a discharge (e.g. the garage). If the water heater is located in an area where the floor could be damaged (e.g. the attic), the pipe extension should be extended to the exterior of the house, discharging within 6 inches of the ground.

by Mark Munsch