Returns should be sized to "comfortably" carry all of the supply without overheating fans/compressors and creating excessive noise, especially at the return intake. If the return is not large enough, air at the return accelerates (and noise increases, whistles, etc.) to keep the necessary volume up. Restricted air flow not only makes a system less efficient, it can overheat and burn out heat pump/cooling system compressors; this is why it is important to replace filters often - to maintain efficient air flow. There is a formula or rule-of-thumb the heating/cooling guys use to size return ducts vs supply ducts; 'knew it years ago; I've forgotten.
Wilton ----- Original Message ----- From: "Peter Hertzing" <phertz...@gmail.com> To: "Mercedes Discussion List" <mercedes@okiebenz.com> Sent: Sunday, March 15, 2009 8:16 AM Subject: Re: [MBZ] OT - Stupid Wilton - Thanks for the great info. I have question. Is thier a magic formula for calculating the amound to return vs. supply? Should it be equal, or shoudl one or the other be larger? Thanks, Peter On Sat, Mar 14, 2009 at 8:45 PM, Wilton Strickland <wilt...@nc.rr.com>wrote: > 'Sounds like you may have an intake/return leak. I have found several (at > least 3 during the 15 years I inspected domestic systems) with the return > ducts lying COMPLETELY open under houses - ALL the air exiting supply > registers in the house was coming from under the house! I've seen many > others with lesser leaks, of course. We do need to be aware of those > possibilities, understand what happens in the system and try to close those > leaks on BOTH sides of the system. Duct leaks on both sides of the system > do a good job of removing money from our bank accounts and fatten those of > the power companies. > > Most heating/cooling system ducts I've seen are VERY poorly installed and > leak like sieves. Most I've seen are assembled very loosely with worthless > "duct" tape that falls off 'bout the time the check to the installer > clears, > screws or staples with lotsa leaking cracks. Check the ducts thoroughly > and > try to seal them as completely as reasonably possible. Seal leaks with > mastic and/or a VERY good tape (NOT so-called "duct/duck" tape) made > specifically for really sealing ducts - the very sticky, shiny, metallic > tape is usually good for it, and there may be better stuff now. There are > companies who do a pressure (fan door) test of duct systems with aid of > "smoke candles" to find leaks and then work to seal them. 'Been 8 years > since I did an inspection, so I've lost touch with costs, etc. > > Wilton > > ----- Original Message ----- > From: "Archer" <arche...@embarqmail.com> > To: "Mercedes Discussion List" <mercedes@okiebenz.com> > Sent: Saturday, March 14, 2009 3:24 PM > Subject: Re: [MBZ] OT - Stupid > > > Hi Wilton, > Here's another A/C question you or someone else might be able answer. > Because the electric bill seems high, I suspected that there might be a > leak > in the fiberglas ductwork Since this is a "closed" A/C system with no > fresh > air coming in except when the doors or windows are open, I concluded that > if > I opened a window a few inches and taped a kleenex in the opening that I > could tell if a leak in the return ductwork was sucking in air (gaining > air) > which would make the kleenex billow out; or if a leak in the ductwork to > the > cold air registers was blowing cold air out in the attic which would make > the kleenex billow in (losing air). > It turned out that the kleenex billowed out which meant that there was a > leak in the return ductwork in the attic and the house was gaining air from > the attic. Where was this excess air going? I would guess it was going > out > through the usual leaks around the doors and windows or even up through the > range hood vent or other vents. > > When we first built the house about 13 years ago, I did the same "kleenex > test" and found that there was a "big leak", so I called the company that > installed the A/C. He went over it with his gauges and instruments and > said > there was no leak. I tried to explain that since the house was losing or > gaining air there had to be leak, but I was never able to make him > understand that there had to be a leak. After waiting a a couple of weeks > deciding what to do, I did the test a second time and there was no leak. > The Kleenex hung straight down. I guessed that since the ductwork was put > together with staples and duct tape that a loose area of duct tape had > "resealed" itself. > (Note: Using a kleenex, I made sure there was no inside or outside air > movement that might have blown the Kleenex taped in the open window.) > > Since I was only using simple physics for the tests, I'm wondering if the > A/C guy was right and I was wrong since he knew a lot more than I did about > ducted A/C systems? > Thanks, > Gerry > > ------------------------------------------------ > From: Wilton Strickland > Several days ago, somebody was talking about doing something stupid. > "Don't > remember who it was, but be reassured whatever it was probably wasn't so > stupid. Now, let me tell you about stupid; THIS was stupid: > > WHERE IS ALL THE WATER COMING FROM? > By > Wilton Strickland > > During the summer of 2000, while I was working as a private, independent > home inspector and building consultant, I received a call from a woman who > was extremely concerned that her new house had excessive moisture on the > underside and did not have an adequate vapor barrier. (A vapor barrier is > usually formed in the under-floor crawlspace by laying a plastic > sheet/membrane on the ground to keep water vapor from rising out of the > ground and through the floor into the house.) She said she had a wet wall > and lots of water on the floor in a bathroom; she called a plumber who had > been unable to find any leak and had told her that her problem was “no > vapor > barrier under the house.” She had also called a roofer, who could find no > problem with the roof. Because the house was only a few months old, she > wanted a licensed, professional inspector to document the moisture problem > under the house in order to persuade the builder to correct it. > > She had described the house as being a one-story structure of about 1800 > square feet. When I arrived at the house, though, I immediately saw that > it > was a “double-wide” manufactured home on a permanent, full masonry > foundation. From what she had described on the phone, I was expecting to > find a typical “poor drainage” problem around the outside causing water to > accumulate under the house. Ground around the outside of the house, > however, was well-drained, and quick observations of the underside via the > crawlspace access door and foundation vents revealed a reasonably dry > crawlspace and an intact, factory-installed vapor barrier attached to the > underside of the structure. While I was walking around the outside, > looking > through foundation vents, etc., the lady continued to tell me how wet it > was > inside the house, and asking, ”Where is all the water coming from?” > > Shortly, I was ready to see the interior and the water that she was > concerned about. I followed her into the house and into a bathroom, where > the door was standing open against an adjacent wall. As she pulled the > door > away from the wall, I noticed that a large section of wallboard/sheetrock > on > the wall had been removed, and the backside of the door, the remaining > areas > of the wall and the cabinet in front of the door were dripping wet. A > couple of wet towels were on the floor beneath the door. There was a > strong > blast of very cold air coming from the heating/cooling register in the > floor > behind the door. She told me that when they removed the wet wallboard, > they > found a lot of water accumulated inside the wall. I knew immediately that > the water was condensation caused by the blast of cold air flowing in the > confined area between the door, the wall and the cabinet. I laid a > thermometer on top of the cabinet with the probe tip hanging off the edge > so > that the air could flow across it. After a very few minutes, while I began > to explain condensation to the lady, I checked the thermometer and found > the > temperature of the air at the top of the cabinet to be 56F! The wall, the > door and the front of the cabinet were acting as large condensing plates - > water was dripping profusely off the bottom edges of them. > > I tried to explain condensation to the lady, but she could not, or would > not, understand me. First, I tried to get her to understand that the air > all around us contains lots of water as a vapor that we usually don’t see. > Warm air can hold more water than the same air when it is cooler. When air > cools below the dew point, the temperature at which air is saturated or > holds all the water that it can at that temperature, some of the water > vapor > must condense and can be seen as fog, clouds, rain, snow, sleet or hail, > depending on temperature of air that the droplets of water may fall > through. > Dew on grass, condensation on the outside of a cold drink glass and the > water dripping from the surfaces in her bathroom are caused by the air in > contact with the cold surfaces being cooled below the dew point. The > constant blast of very cold air behind the door makes the surfaces cold > enough to cause the condensation to form on them - just like a cold drink > glass and windows inside a car on a cold day. The lady’s eyes had a > constant “glaze” of stupidity with no understanding of my explanation of > simple condensation as she continued to ask, “But where is all the water > coming from?” > > I tried, again, to tell her that the air all around us just naturally > contains lots of water. The amount of water in the air is constantly > changing as temperature changes, as weather changes. The air around us is > saturated, or full of water, when it rains. After a rain, some of the > water > soaks into the ground, much of it evaporates back into the air around us > and > rises away to be seen as clouds or to rain again another day. Inside the > house, water comes from several sources. First, air going into the house > from outside takes with it whatever water it accumulated by evaporation > from > outside. Additionally, we people, just by living, put a lot of water into > the air by breathing, perspiring, constant evaporation from our bodies, > etc. > Cooking, laundry and bathing/showering also put a lot of water into inside > air. We can’t live without putting water vapor into the air around us. > Still, the lady asked, “But where is all the water in the bathroom coming > from?” > > Because I had not seen the heating/cooling system thermostat in the usual > place near the return register in the hall near the bathroom, I stopped > trying to explain the situation for a moment and asked to see the > thermostat. She took me down the hall and through a closed door into a > bedroom, where the thermostat was located. She told me, “We never use this > room - the registers are closed and we keep the door closed.” The > thermostat was set at 67, but because it was isolated from the rest of the > house, it could never shut the system off; it never shut off during my > visit. I told the lady that the thermostat should be moved to a point near > the return register in the hall and should be set no lower than about 76. > When I suggested the more reasonable setting, she exclaimed, “Oh, but we > like to keep the house really cool!” (BTW, outside temperature was about > 95F.) I reminded her that by try to keep the inside of the house so cool, > she has condensation dripping off those surfaces in the bathroom. Back in > the kitchen, she showed me another wall that often gets wet. This wall > also > had a constant blast of 56-degree air on it from a floor register. > > Meanwhile, I stepped outside for a couple of minutes to check the size of > the cooling system. I found it to be a 4½ ton unit! Using a “rule of > thumb” of a ton of cooling for each 600 square feet in a typical house, > the > unit was over-sized by about 1½ tons! As I went back inside the house and > began to try to tell the lady that the cooling system was too big for the > house, that it produces lots of very cold air, but it never shuts off > because of the bad thermostat location, her father-in-law arrived and > asked, > “Where is all the water coming from?” > > With him, I had to start at the beginning, and, again, he evidently could > not, or would not, understand anything I told him about the source of the > water in the bathroom and the associated problems with the cooling system. > As I was beginning to “wind down” with the father-in-law and realizing that > he did not understand me, either, the lady’s husband arrived. Hoping that > he may be able to understand me, I had to start at the beginning, again. > He, too, interrupted occasionally by asking, “But where is all the water in > the bathroom coming from?” > > Several times, I tried to tell them that the thermostat should be in the > hall hear the return register, air flow to the register in the bathroom > should be reduced, the heating/cooling system should be properly sized for > the house, the factory-installed vapor barrier attached to the underside of > the house is sufficient and is in good condition, and there is no excessive > moisture problem under the house. After an hour and a half, or more, of > detailed explanations about basic meteorology, thermodynamics, air flow, > etc., with references to cold tea glasses and cold car windows in winter, I > still was getting the same question, “But where is all the water coming > from?” Because of the blank stares and doubting looks from all three of > them, I finally had to say, “I don’t know how else I can tell you, I just > don’t think I’m smart enough to explain it to you.” In exasperation, I > said, “Please, just let me go. There’ll be no charge. I just need to go.” > The lady then asked, “May we get a written report?” I replied, “Then, I’ ll > need a fee. I don’t know how else to explain it to you. Just let me go.” > I just wanted to get out of the situation and have nothing else to do with > them. I just could not get them to understand that the solutions to their > “problems” were VERY simple, and that they, themselves, created a large > part > of those “problems” by keeping the thermostat isolated and by trying to > keep > the inside of the house so cold. > As I drove away, I said aloud to myself, “What a pity. Ignorance can be > cured with knowledge, but stupidity lasts forever.” > Yeah, I guess I was stupid, too, for not writing a report and getting a > fee, > but by then, I just wanted to be FREE of them! > Wilton > > -------------- next part -------------- > > No virus found in this outgoing message. > Checked by AVG - www.avg.com > Version: 8.0.237 / Virus Database: 270.11.13/2001 - Release Date: 03/14/09 > 06:54:00 > _______________________________________ > http://www.okiebenz.com > For new and used parts go to www.okiebenz.com > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > > > _______________________________________ > http://www.okiebenz.com > For new and used parts go to www.okiebenz.com > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > -------------- next part -------------- An HTML attachment was scrubbed... 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