They're coming for your Air Conditioners!

[sjfcontrol]

I wanted to be sure folks did not misunderstand and think you meant to leave the fan set on. This causes humidity to rise drastically in a house.

What would make that happen?

Your duct work runs through a very hot unconditioned space. As the cooler air from the conditioned space circulates through the duct work it absorbs heat from the attic. Like a heat exchanger. If each pass of the air through the ducting picks up even 1 degree of heat, the cumulative affect can add up to a significant rise. Think about what happens when you fill a glass full of ice water and set it on the counter. the outside of the glass begins to get moisture on it. The same will happen from the cooler air in the home circulating constantly through the warmer duct running through the attic. Not nearly as dramatic, but enough that the humidity levels in the home will begin to rise. This doesn't happen when the air conditioner is running and circulating refrigerant through the evaporator coil because humidity is being removed at a rate greater than the rise caused by the duct work.

A secondary problem, is that the blower motor is using electricity and that will result in a rise in your electric bill. A blower motor running 24/7 can consume more energy than many folks realize.

Some programable thermostats have a third option for the fan called circulate. This setting brings on the fan long enough to move the air around, but not long enough to create extreme temperature gains or humidity level increases. This is primarily for air cleaning purposes and has a secondary benefit of moving the stagnant air around the house with minimal affect on humidity levels.

Thanks. When I was having issues with one of my systems, I tried leaving the fan on, with the idea it would help circulate air from the colder areas to the warmer ones. Eventually it just seemed to be heating the air, I figured because it was cycling thru hot attic ducts. So I quit doing that.

[03Lightningrocks]

I wanted to be sure folks did not misunderstand and think you meant to leave the fan set on. This causes humidity to rise drastically in a house.

What would make that happen?

Your duct work runs through a very hot unconditioned space. As the cooler air from the conditioned space circulates through the duct work it absorbs heat from the attic. Like a heat exchanger. If each pass of the air through the ducting picks up even 1 degree of heat, the cumulative affect can add up to a significant rise. Think about what happens when you fill a glass full of ice water and set it on the counter. the outside of the glass begins to get moisture on it. The same will happen from the cooler air in the home circulating constantly through the warmer duct running through the attic. Not nearly as dramatic, but enough that the humidity levels in the home will begin to rise. This doesn't happen when the air conditioner is running and circulating refrigerant through the evaporator coil because humidity is being removed at a rate greater than the rise caused by the duct work.

A secondary problem, is that the blower motor is using electricity and that will result in a rise in your electric bill. A blower motor running 24/7 can consume more energy than many folks realize.

Some programable thermostats have a third option for the fan called circulate. This setting brings on the fan long enough to move the air around, but not long enough to create extreme temperature gains or humidity level increases. This is primarily for air cleaning purposes and has a secondary benefit of moving the stagnant air around the house with minimal affect on humidity levels.

Thanks. When I was having issues with one of my systems, I tried leaving the fan on, with the idea it would help circulate air from the colder areas to the warmer ones. Eventually it just seemed to be heating the air, I figured because it was cycling thru hot attic ducts. So I quit doing that.

You made me type all that stuff and you already knew the answer? Was that a test? Did I pass? LOL...

[sjfcontrol]

I wanted to be sure folks did not misunderstand and think you meant to leave the fan set on. This causes humidity to rise drastically in a house.

What would make that happen?

Your duct work runs through a very hot unconditioned space. As the cooler air from the conditioned space circulates through the duct work it absorbs heat from the attic. Like a heat exchanger. If each pass of the air through the ducting picks up even 1 degree of heat, the cumulative affect can add up to a significant rise. Think about what happens when you fill a glass full of ice water and set it on the counter. the outside of the glass begins to get moisture on it. The same will happen from the cooler air in the home circulating constantly through the warmer duct running through the attic. Not nearly as dramatic, but enough that the humidity levels in the home will begin to rise. This doesn't happen when the air conditioner is running and circulating refrigerant through the evaporator coil because humidity is being removed at a rate greater than the rise caused by the duct work.

A secondary problem, is that the blower motor is using electricity and that will result in a rise in your electric bill. A blower motor running 24/7 can consume more energy than many folks realize.

Some programable thermostats have a third option for the fan called circulate. This setting brings on the fan long enough to move the air around, but not long enough to create extreme temperature gains or humidity level increases. This is primarily for air cleaning purposes and has a secondary benefit of moving the stagnant air around the house with minimal affect on humidity levels.

Thanks. When I was having issues with one of my systems, I tried leaving the fan on, with the idea it would help circulate air from the colder areas to the warmer ones. Eventually it just seemed to be heating the air, I figured because it was cycling thru hot attic ducts. So I quit doing that.

You made me type all that stuff and you already knew the answer? Was that a test? Did I pass? LOL...

No, not a test at all. My question was specifically about a rise in humidity, as you originally stated. If you'd said it would heat the air while going thru the attic, I wouldn't have asked. Frankly, I'm still not convinced about they humidity -- but the air DID get warmer.

Soo.. You get condensation when you cool warm, saturated air. When you're running on the fan alone, you're warming the cool air in the duct. The only warm air that you're cooling would be in the attic itself. i don't see how that raises the humidity, but I'll defer to the expert!

[03Lightningrocks]

Soo.. You get condensation when you cool warm, saturated air. When you're running on the fan alone, you're warming the cool air in the duct. The only warm air that you're cooling would be in the attic itself. i don't see how that raises the humidity, but I'll defer to the expert! [/quote]

Try it and check the humidity before and then after you do it... ... then give me the "scientific explanation" for why it happens.

[Cobra Medic]

Are we talking about relative humidity or the absolute moisture content in the air?

[Winchster]

He didn't mention it but

The turnover in a house is pretty good, meaning you're also pulling warm humid air from outside. And warm air by default raises the relative humidity.

[03Lightningrocks]

He didn't mention it but

And warm air by default raises the relative humidity.

And... relative humidity is what one is actually feeling. It is what makes you feel uncomfortable and sweat.

[Winchster]

He didn't mention it but

And warm air by default raises the relative humidity.

And... relative humidity is what one is actually feeling. It is what makes you feel uncomfortable and sweat.

Exactly.

[JP171]

I gather it's illegal for a homeowner to buy the equipment and supplies, and service his own equipment? That gauge header can't be that expensive. With three units, it'd pay for itself.

I can't fathom how it would be illegal ... but law makers can be a sneaky bunch. Maybe some of the suppliers don't like to sell to "the public" but I doubt it's illegal. Check the internet.

I seem to recall hearing that you need a license to do any HVAC work that might result in a release of refrigerant. That would be enforced by requiring a license to buy the refrigerant, and possibly the metering tools. But I don't know that for a fact.

LOL... I don't think it was meant to corner the market. sjfcontrol has it right, it is an EPA regulation that began in 1993. The idea was to reduce the damage being done to the Ozone layer by refrigerants through proper training and certification. GOOGLE Montreal Protocal for further information.

didn't read the whole thread but no you DO NOT need a license, you need an EPA Certification and a TDLR use and purchase certification. A home owner is allowed to service and repair his own equipment at his home or anyplace he owns or rents. A city may refuse to grant a permit for replacement or installation of a new unit but repaires don't require a permit. and the gauge manifold can run from about 30 to well over 500$ meters run from again 30 to several hundred dollars and you don't need anything to purchase the tools. and yes I am licensed at the Class A level have been for, hmmm oh about 20 years

[C-dub]

You made me type all that stuff and you already knew the answer? Was that a test? Did I pass? LOL...

There are a whole bunch of things that I think I know, but always forget to look up to confirm or repudiate my theory. I appreciate your confirmation of my thoughts on this subject.