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Blower Speed for furnaces


msteger
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I was at a home inspector seminar a few days ago where the presenter was discussing furnace blower speeds. He said that slowing the blower speed in heat mode can allow for more heat into the home and lower utility bills (due to more even heat and less power consumed). The idea sounds valid.

I noticed that my Carrier Weathermaker 9200 has the fan set (for heat mode) to low-medium by manufacturer default. Do you heating guys recommend trying a gas fired furnace is low blower speed for the reasons the presenter mentioned?

Of course, I'd leave the fan speed on High for A/C mode.

Just curious...

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I'm not a heating guy, but it sounds like nonsense to me. I think it would have the opposite effect.

Assuming that the burner is putting out a constant amount of heat, reducing the fan speed will cause the temperature of the air being delivered to the house to increase. So much for his "more even heat theory". And since a furnace has no way to store heat, the exhaust temperature will also increase, meaning more heat will be lost through the exhaust.

I would have just LOVED to have heard EnergyStar's take on this. Dang!

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The key is to set the fan so it meets the manufacturer required temperature rise (which is located on the furnace). Depending on a few factors, that could be the setting from the factory or it could be a different setting such as medium speed (similar to a temperature drop for the air conditioner).

For more even heat, properly sizing the furnace for the house and properly installed heat and return ductwork is more of a factor.

These two things are the most important in my opinion.

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There are factors before lowering that blower to low speed. What type of filter is installed, is there an air conditioner coil installed. What type of return air drop (Flex compared to metal), size of the return air drop and even where the hole is cut in the blower compartment for the return drop (right side, back, left side or bottom). Note: All just mentioned is beyond what a home inspector needs to know.

msteger

I noticed that my Carrier Weathermaker 9200 has the fan set (for heat mode) to low-medium by manufacturer default. Do you heating guys recommend trying a gas fired furnace is low blower speed for the reasons the presenter mentioned?

To answer your question direct. As a past heating tech of 10 years, I would not recommend setting your fan from low-medium to low.

If you do, just make sure your temperature rise is still in line with the information on the furnace. You don't want that heat exchanger getting too hot and wearing out prematurely.

I disagree completely with the statement that lowering the blower speed will allow more heat into the house. It just feels warmer only.

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I was at a home inspector seminar a few days ago where the presenter was discussing furnace blower speeds. He said that slowing the blower speed in heat mode can allow for more heat into the home and lower utility bills (due to more even heat and less power consumed). The idea sounds valid.

I noticed that my Carrier Weathermaker 9200 has the fan set (for heat mode) to low-medium by manufacturer default. Do you heating guys recommend trying a gas fired furnace is low blower speed for the reasons the presenter mentioned?

Of course, I'd leave the fan speed on High for A/C mode.

Just curious...

Maybe it's just me, but I'd call Carrier, get a tech on the phone, and ask the tech to tell me if the presenter is correct or a folklorist. (As we all know, there's plenty of folklore blowing out of HI "schools.") I think I'd get a better answer from a manufacturer's tech than I would from an HI "instructor." (As we all know, HIs' opinions vary all over the place...)

Speaking just for myself, I wouldn't change anything on the say-so of an HI "instructor."

WJ

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During the winter months, we often close the window that is closest to the fire a couple of inches. That smaller window opening lowers the amount (speed) of the wind blowing through the house and allows for more heat to escape from the smoke. In the summer we will open that window fully up to allow more wind to blow over the ice, for cooling purposes. So, I guess he is right.

For the record I think your instructor is a tad on the goofy side and likely is not used to being challenged. Call a couple of furnace tradespeople or mfg rep.

This reminds me of an old friend of many inspectors that claimed air moving through ductwork approaches 400miles per hour!

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I dunno,

There might be something to it. I'd always thought it was goofy that when I increase the heat in my car the fan would automatically slow down on certain settings. I thought it might just be that brand car or that I might have a bad switch but when my wife got her beamer I discovered that when the heat is thermostatically controlled the fan actually runs slower for higher heat.

ONE TEAM - ONE FIGHT!!!

Mike

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The main system in my home has a three speed blower.

I have a three speed blower also. The first setting is when the burner is burning at low fire (40,000 BTU's); the second is when the burner is burning at normal fire (60,000 BTU's); and the third speed is when the air conditioner is running. My parents had basically the same furnace only they had a fourth speed so when there was no call for heat or cooling, the blower would run really slow to keep the air circulating throughout the house plus it constantly filtered the air that passed through the hepa filter.

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