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Old 04-05-2012, 06:45 PM   #1
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I have been having trouble with my air conditioner, but no problem with my heating. I have a 2,150 sq. ft house. It's a one and a half story home with 4 skylights, high ceilings and lots of windows. I live in Ohio so my furnace is used more than my air. I have gotten 6 estimates from different heating and cooling contractors and some things they agree on, and other things they are totally different on. Most of them agree I have improper return air or I don't have enough. They suggest I need at least three to four supply lines. I have a Goodman 10 seer 3 ton air conditioner which was installed around the year 2000 when the home was built. The furnace was replaced in 2005 and is a Goodman GMS909904CXA. It is a 92,000 input and 86,000 output. I have been told I need a 2 stage furnace. If I only install a 3 ton 13 seer air conditioner they say it will only improve very little. They state I need to match air and furnace for best results. Did lots of reviews on the literature they have given me on their brands of air conditioners and have gotten good and bad ratings from everyone. I just don't know what system in a 3 ton seer I should go with. They all think I should have a single stage air conditioner and a 2 stage furnace. This is because it runs more hours in the winter season and less in the summer, and it is much more efficient. Can provide much more information if needed. Would appreciate all your help!!!! Very confused!!!!


Last edited by mammaw810; 04-05-2012 at 06:48 PM.
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Old 04-05-2012, 07:13 PM   #2
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A 2 stage is no more efficient then a single stage furnace. The only savings from a 2 stage is that many people find they can set their thermostat lower because of the longer run times eliminating much of the cool draft feeling. But it needs to be sized right, not over sized.

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Old 04-05-2012, 08:06 PM   #3
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3 Tons for a 2100 sq ft house seems very high to start with especially in Ohio.
If you are going to buy a new furnace and a/c unit,why not do the job right?
I would not even talk to any contractor that will not give you a manuel "J" AND a manual "D"so that you at least know for sure what your house needs.
For my relatives I have only installed a 2 stage furnace believing that in the spring and fall they do not need the full size of a winter furnace.
The thing is is that even if you buy the most bells and whistles if the size is wrong you don't get any savings and if the duct SYSTEM isn't good you lose effiency that way.
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Old 04-06-2012, 08:17 AM   #4
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I'm not quite sure what a manual J and a manual D is. Can you explain what that is ? Would really appreciate it. Thanks!!!
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Old 04-06-2012, 08:26 AM   #5
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I'm going to weigh in on the side of upgrading the ductwork. You said it yourself in your first post, you need to match the airflow to the furnace. Without even seeing it I can tell that you have a problem child. 4 skylights will suck so many btu's out of a house it isn't funny, add large expanses of glass plus high ceilings and you have a monster. Good airflow and circulation is a must, particularly in your application. Fix one thing at a time don't get wrapped up in all of this equipment buying and shotgun approach. Upgrade the ductwork and have it professionally balanced to what it should be and see how much improvement or not there is and then move on to the next item. It sounds like things are working so there is no need to panic and buy out the store. You need to tweak and improve. Patience lad, you'll get it figured out. Remember cost versus benefit. Pocketbook first!
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Old 04-06-2012, 12:00 PM   #6
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Originally Posted by mammaw810 View Post
I'm not quite sure what a manual J and a manual D is. Can you explain what that is ? Would really appreciate it. Thanks!!!
Manuals J and D are engineering calculations that allow people to figure out exactly what your heat loss/gain is for each room and the "D" tellsm you what size duct you need in order tom supply each room with enough BTUs to satisfy it.
It requires that they measure each room,each window etc.I used to do the long form with a calculator and penciel but these programs are now availiable for computer use where you plug in all the measurements etc and it automaticly gives you your answers.
It used to be only the very best contractors would do this but it is really quite common now and only the lazy contractors will not do it.
In some areas of the country is is now required when you pull a permit for installation of a new house OR a replacement.
The day of putting ones finger up in the air to guess is now over.Nobody in their right mind would buy a furnace without these two calculations.
For more info you can google it and get a ton of information.
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Old 04-06-2012, 03:33 PM   #7
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Thank you so much REP for your information. I will check it out on the google sight and hope for the best. Everyone has been helpful and we really appreciate all the information we can get. Today you get told very little from professionals for some reason. They only tell you things when you ask, they never volunteer any more information unless they have to. I don't quite get that. Once again thanks to all of you. We haven't went forward with this project until we know for sure what we are doing. We don't want to put a lot of money in an air conditioner and still have the same problem. Right now when we run our air conditioner sometimes it runs for 12 hours when it is really hot outside. Trying to fix this problem and hoping for the best.
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Old 04-09-2012, 06:57 PM   #8
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Originally Posted by GarryE View Post
I'm going to weigh in on the side of upgrading the ductwork. You said it yourself in your first post, you need to match the airflow to the furnace. Without even seeing it I can tell that you have a problem child. 4 skylights will suck so many btu's out of a house it isn't funny, add large expanses of glass plus high ceilings and you have a monster. Good airflow and circulation is a must, particularly in your application. Fix one thing at a time don't get wrapped up in all of this equipment buying and shotgun approach. Upgrade the ductwork and have it professionally balanced to what it should be and see how much improvement or not there is and then move on to the next item. It sounds like things are working so there is no need to panic and buy out the store. You need to tweak and improve. Patience lad, you'll get it figured out. Remember cost versus benefit. Pocketbook first!



GaryE
I am taking your advice. Thank you so much for all your information. I have added cold air returns higher on the walls just above the ones on the floor. I will use the lower ones for heat, and close the top ones, then use the top ones for air, and close the bottom ones.
I have a high efficent furnace and the exhaust pipe is vented through the wall but my combustion pipe is inside for fresh air. Everyone that has seen this, stated that it also should be vented through the wall with a 3" pipe. This would make my furnace more efficent. Also I have an 8" supply line running off the Plenum which doesn't do anything, ( heat or air]. I have been told the air is shooting right over top of it because that is a compression area. It is right where the supply runs takes off from the main body. I already have two 6" supplies on the main body and adding the 8" supply to the same area would starve out the other two. The two 6" supplies work real well. It has been suggested to move down the supply run from the main about 5 feet leaving the 8" on the plenum and then add a damper. This way we can control the amount of air flow for the 8". I'm not real sure how to install the damper since the run is an 8x22. This would make such a big difference without moving the 8" from the plenum. How do you know if your furnace blower motor is moving enough air? I have checked the diagram and it has all the proper settings, and it still seems to be running a little slow. I have double filters and an electronic air cleaner. Does this restrict some of my air flow? I am told my furnace has a 4 ton capacity which would handle a 3 1/2 ton air conditioner, approx. 36,000 BTUs.
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Old 04-09-2012, 08:26 PM   #9
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what are double filters...
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Old 04-10-2012, 08:20 AM   #10
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what are double filters...
that would mean I have two filters on my furnace.
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Old 04-10-2012, 08:27 AM   #11
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side bye side.... not back to back I assume....
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Old 04-10-2012, 08:50 AM   #12
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your question of how do you know if you systems are moving enough air, was not really answered.

I am not a pro here, but what I have found is that there are a couple of ways to do it.

1, measure the flow out of each supply and also measure intake at the returns. This too can be done a couple of ways. You can have someone with an expensive flow hood measure, then you know for sure. You can get a hand held anemometer and do it yourself, this is ok for gross measurement, but normally requires some math calculations. You could also get a manometer and check the static pressure of your system, then compare that to the listed air flow charts from your system manufactuer. any of these ways will give you a better idea of what your current system is delivering for your dollar spent on heating and cooling

2. Once you have the figures, you can then used a software program (like hvac calc, here on this site) and figure out what each of your rooms requires, at a given high and low temps for your area.

Armed with the flow rates and each rooms btu/air supply need numbers, you will then know better what each room needs and if you system can deliver!!!! its not easy to understand, but its not rocket science either and its not like you are a pioneer in the hvac world...lol. Its really pretty cool (pun inteneded) when you can take the bull by the horns and really dig into the education/testing and become a well informed consumer!!!!

lets face it the Professional guys, just dont have the time (which equals money) to do the full on research you need for your home. They are skilled at many things, but they do not have time to do a full audit for each and every single homeowner out there. so they use rules of thumb and their experiance in the industry. This is not a knock to the pros, but just a fact of life. you dont need to be a pro either, but armed with diy education you can make a great decision on your hvac system!!!!!!!!!
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Old 04-10-2012, 11:26 AM   #13
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side bye side.... not back to back I assume....

that is correct

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