Comments on: Don’t Set Your Air Conditioner Thermostat Like This

By: ruben

ruben — Thu, 16 Oct 2014 00:07:42 +0000

I have kept my fan on since
I have kept my fan on since the day it was installed. First reason to have it on all the time, air filtration. Second is to get hot spots in the house. The fan on is used during the middle of the seasons where you don't need either heat not cool. But it's dry in Arizona. I've never heard of mold in duct work. Must be very wet.

By: David Butler

David Butler — Sun, 28 Sep 2014 22:58:30 +0000

@Evelyn, the additional
@Evelyn, the additional energy required to run continuous fan for that period (8 hrs) is probably on the order of $3 to $8 a month, depending on your blower size, electric rate and how many hours the blower would have operated to satisfy heating or cooling calls. This amount can easily be obscured by monthly fluctuations.

If you live in a humid climate, you should keep an eye on indoor RH to make sure it doesn't get too high. Anything over about 60% is a red flag.

By: David Butler

David Butler — Tue, 08 Jul 2014 22:17:40 +0000

@Valeri, you can't just add a
@Valeri, you can't just add a thermostat to an existing air conditioner.

Since you already have two AC's, then you must already have two thermostats, no? Normally, a two story home with two AC units will have one system per floor with a thermostat on each floor. But without more information on how your system is laid out, there's no way to offer specific advice.

The common problem you describe (upstairs warmer than downstairs) is almost always the result of a poorly designed air distribution system (ducts) and/or defects in the building envelope (usually both).

See my replies and Allison's to a similar question here for more information: Oooh, Shiny Stuff! - Radiant Barrier Fundamentals.

By: Thomas Clark

Thomas Clark — Tue, 08 Jul 2014 21:33:12 +0000

Hey David, Just read your
Hey David, Just read your answer to Jessica. Thought she may have a Hunter Prog. t'stat with fan refresh setting. Turns the fan on independently according to preset time intervals. Only time I have seen one like this is in my new home. Hope this helps. Tom C.

By: Valeri Stroner

Valeri Stroner — Tue, 08 Jul 2014 20:30:22 +0000

We have a two story home.
We have a two story home. Our upstairs is much warmer than the main level. We do have two ac units to accomodate the size of the house but my question is do we need an additional thermostat upstairs?

By: David Butler

David Butler — Sun, 06 Jul 2014 22:39:36 +0000

@Jessica, when the t'stat is
@Jessica, when the t'stat is set to Auto, the blower will not turn on between heat or cool cycles, or when system is turned off.

Most thermostats include a mode that will keep the blower on for a brief period (typically up to 2 minutes, adjustable from the installer menu) after the end of a cooling cycle in order to purge the remaining cool air from the ducts. Ditto in heat mode.

By: Jessica

Jessica — Sun, 06 Jul 2014 06:34:17 +0000

I just built the house so the
I just built the house so the system is new etc the fan is set to auto. Is it suposed to kick in when system is turned off?

By: David Butler

David Butler — Wed, 21 May 2014 00:09:54 +0000

@Tom, your post is filled
@Tom, your post is filled with so much misinformation and misconception, I can't fathom a response that would fit on the page.

By: Tom Clark

Tom Clark — Mon, 19 May 2014 19:21:40 +0000

Ladies and Gentlemen, How
Ladies and Gentlemen, How much humidity are we talking about here ? If cost is the only factor then the above upper estimate of $250.00/yr or $20.00/mo. is worth the savings and comfort associated with constant fan operation ! Last year after considering the advice in regard to Fan "on" operation. I placed a Humidistat in the enclosed crawl space of my home and another in the living space. The humidity level has never gone above 52% in the past 18 mos. despite leaving the fan run continuos 24/7. I have observed the gravity drain flows whenever the Outdoor unit is running. There is little condensate/moisture left in the drip pan. I have not had any humidity problems in the home since enclosing the crawl space and installing a dehumidifier in same. The dehumidifier drains to the outside as well. This drain flows intermittently all year long. Ten years ago after the home was finished and the crawl space was left with inadequate ventilation. The pre-finished Hardwood Floors all buckled on the first floor !! The builder concluded there was too much moisture in the floor. Agreed to correct all defects associated with the excessive crawlspace humidity. The crawl space was then enclosed and outfitted with the correct auto dehumidifier and constant gravity drain to the outside ! Problem solved. However the builder consulted with the HVAC installation contractor who said the floor defects were caused as a result of the 24/7 fan operation ! So 10 years later the floors remain cupped and buckled as they were when we first moved in ! I have consulted with many HVAC Manuf., contractors, technicians, and engineers as well as worked in the HVAC field primarily in the North East. None of these industry professionals agree with the fan operation be capable of causing the floor to swell to this extent ! I have clearly shown the fan "on" setting has not had the effect on Humidity in the home as described in the article or subsequent posts. Now the fan on setting allows for a higher temp. setting due to convectional cooling effect (breeze) It also eliminates awareness of system cycling. I have allergies and appreciate the benefit of constant filtration of the indoor air. I am sure to check and replace the return air filter on a as needed basis or every 3-6 months as manuf. recommends. In addition my assertion regarding separate heating and cooling is because the best way to heat is with Radiant heat not blown air !! (breezes) and hot air rises ! Heat needs to be down where the people are not up at the ceiling ! The most comfortable heating systems heat the objects in the room not the air ! These two systems are designed to do two different things. We should Cool with a cooling system and we should be heating with a system designed to heat ! More expense but so much more energy efficient and even more comfortable !

By: Allison Bailes

Allison Bailes — Sat, 10 May 2014 16:17:52 +0000

Laurel B.:
Laurel B.: Put your thermostat in the cooling mode with the fan in the Auto setting, especially in a humid climate like Florida.