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Old 07-23-2012, 10:47 PM   #1
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For all the HVAC experts! 2 level difference


Quick background info. i am located on the east coast and it's nice and hot. the house is 3 stories, basement included. the issue is, there is too much of a temperature difference between each level. the basement is the most cool, the 1st level is pretty good, but upstairs in the bedrooms the temperature must be 10 degrees hotter.

so my question is can i somehow improve the ducts so that the top level is just as cool? i am assuming there is a lot of leakage traveling from the basement up to the bedrooms. because on the 1st level it's not bad. appreciate the insight!

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Old 07-23-2012, 10:57 PM   #2
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For all the HVAC experts! 2 level difference


The duct system can have issues but sadly it is mostly due to heat rising. It is going to be hotter as you go up levels in your home in both summer and winter.


You can try to close some vents in the lower levels to force more air to the upper levels. Don't close more than say 20% max of the vents or you may freeze the coil. You will find you will need to reverse this procedure come winter.

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Old 07-23-2012, 10:59 PM   #3
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For all the HVAC experts! 2 level difference


and if you can leave the fan running instead of having it on auto it will help to cycle the air.
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Old 07-23-2012, 11:28 PM   #4
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For all the HVAC experts! 2 level difference


thanks guys. so theres pretty much no retrofit solution? and you are saying to keep it running all the time instead of setting the temp at the thermostat?
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Old 07-24-2012, 05:05 AM   #5
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For all the HVAC experts! 2 level difference


Trying to cool a 2 story home with a single unit is not easy. There's always zoning, where you install electric dampers to control the differents areas (or "zones") of your home. Those zones would each has a tstat, and you could maintain each zone at the desired temperature (for the most part). That said, retrofitting ductwork to handle a zone system can be very, very difficult, especially if your ducts are enclosed in walls, floors, etc.
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Old 07-24-2012, 05:08 AM   #6
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For all the HVAC experts! 2 level difference


How many returns do you have.
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Old 07-24-2012, 08:06 AM   #7
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For all the HVAC experts! 2 level difference


Quote:
Originally Posted by scottmcd9999 View Post
Trying to cool a 2 story home with a single unit is not easy. There's always zoning, where you install electric dampers to control the differents areas (or "zones") of your home. Those zones would each has a tstat, and you could maintain each zone at the desired temperature (for the most part). That said, retrofitting ductwork to handle a zone system can be very, very difficult, especially if your ducts are enclosed in walls, floors, etc.
thanks for your input. yea i think you are right. theres too many zones, and not enough money to install a zone system. what is the normal action in case like this, with multiple levels, which i imagine is prevalent

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How many returns do you have.
upstairs there is only one in the main hallway i believe. i am a complete noob to hvac so i am not even sure how the whole return thing works haha. please enlighten me!
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Old 07-24-2012, 08:15 AM   #8
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For all the HVAC experts! 2 level difference


The problem with multi-story homes, is that most hvac system installers act as if it is a single story structure. What is the model & manufacturer numbers of the hvac equipment? How many returns and what are their locations in the structure? What is the size of the duct work to each floor? Where is the inside unit located?

Now, you can try a cheap fix by closing dampers on various ducts, to see what happens. Also, what is the output temps of the various ducts on each floor, and what is the return air temp at each return? Also how old is the structure, is the attic areas well ventilated, well insulated?

Now, you can try by putting up UV film on the windows on all floors, and use black out drapes. We have found that has worked best with our place, along with having to put in a powered vent fan in our attic, due to poor air circulation, due to no lower input venting into the attic. We have been able to get our attic temp to stay below 110 with the powered vent fan, which also has helped with keeping the house cooler.

Also, basements will always be generally cooler than the rest of the house, due to the ground is a natural insulator.
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Old 07-24-2012, 08:26 AM   #9
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For all the HVAC experts! 2 level difference


very good points! i have no idea what kind of system i have haha. there is a return on each floor. on first level is in the kitchen. on upstairs it's at the end of the hallway. the way the ducts work is the main one runs straight up from the basement, through closet on first floor, to closet upstairs, and branches off from there. should i just opt to get a bigger system?
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Old 07-24-2012, 08:37 AM   #10
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For all the HVAC experts! 2 level difference


Where are you ducts located on the first floor (not the basement)? In the ceiling or the floor/baseboard? I'm assuming they're overhead in the top floor?

If you have separate main trunks for the first floor and the second floor, you could easily zone a system like that, and have a much improved comfort level in your home. If they aren't (and chances are good they aren't), then you're stuck with trying to reduce the load on the house, as mentioned earlier or spending a boatload of money to retrofit what you have now.

The size of the system is not the issue in your case. It's the delivery of the air that is causing you trouble. IMO 2 story homes should never be run with a single unit unless it's zoned, but it happens all the time.
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Old 07-24-2012, 08:43 AM   #11
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For all the HVAC experts! 2 level difference


Quote:
Originally Posted by scottmcd9999 View Post
Where are you ducts located on the first floor (not the basement)? In the ceiling or the floor/baseboard? I'm assuming they're overhead in the top floor?

If you have separate main trunks for the first floor and the second floor, you could easily zone a system like that, and have a much improved comfort level in your home. If they aren't (and chances are good they aren't), then you're stuck with trying to reduce the load on the house, as mentioned earlier or spending a boatload of money to retrofit what you have now.

The size of the system is not the issue in your case. It's the delivery of the air that is causing you trouble. IMO 2 story homes should never be run with a single unit unless it's zoned, but it happens all the time.
on first floor ducts are floor/wall not in the ceiling. top floor its ceiling but inside the attic space. i dont think i have separate trunks because the main duct runs straight up through 2 closets, with branches coming off.

so in my case i should get a 2nd unit?
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Old 07-24-2012, 08:57 AM   #12
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For all the HVAC experts! 2 level difference


If you have separate "trunks" (i.e. main supply lines) for the 1st floor and 2nd floor, you could zone this. If not (and it sounds like you do not), then your best bet would be a second unit to manage the top floor.

If you could take some pictures of the furnace/air handler, including some duct pictures there at the furnace, we might have a better idea of what you're dealing with.
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Old 07-24-2012, 10:07 AM   #13
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For all the HVAC experts! 2 level difference


Quote:
Originally Posted by scottmcd9999 View Post
Trying to cool a 2 story home with a single unit is not easy. There's always zoning, where you install electric dampers to control the differents areas (or "zones") of your home. Those zones would each has a tstat, and you could maintain each zone at the desired temperature (for the most part). That said, retrofitting ductwork to handle a zone system can be very, very difficult, especially if your ducts are enclosed in walls, floors, etc.
I have not found this to be a problem. Properly sized ducts (supply/return) and matching air handler size to the ducts / heat load will correct this. Additionally, the use of jump or transfer ducts helps also.

so what could be the issue.

my guess from 4000 miles away...

1. air handler / tonage way to big for the building or to big for the ductwork. Lots of people and contractors like to think bigger is better, in fact the HO in this thread said "may I need a bigger system". Bigger is not better. bigger leads to short run times on the hot days and does not allow the air to circulate. This the "fix" of keeping the fan running all day. Note that this idea is not economical as the ducts may be picking up heat load and or leaking. The leaks may create a negative pressure in the house and cause additional heat load...

2. static pressure. if the returns are too small or restrictive filters are used, the speed of the air in the system is slowed. if the volume of the air in the system is slowed there is no mixing of the air and of course heat rises and the upper floors get hot. The supply side ducts could be too small for the air handler. Typically the installers will slow the fan to reduce the static pressure, whic leads to low air speed and low volume.

so what do to?????

first off check your delta t. The Delta t is the temp of the air comming into the air handler and the temp going out the other side. you may need to drill a small hole in the ducts (NOT THE AIR HANDLER!!!!) to insert your themometer. 15 to 20 degrees difference is what you are looking for. higher (like 30 or 40) means the air is too slow... lower (like 5 or 10) means that the air is too fast.

Next thing to check is the static pressure of your system. Use the same holes and use a manometer (fairly cheap on ebay). You want one what will measure up to about 2 inches of water. Analog or digital, its your dime, so pick what your comfortable with.

next thing to check is the air speed and volume at each of your supplies. use an anemometer for this (again cheap on ebay). be sure to get one that does cfm and air speed (fpm). also check the returns for FPM. This should be less then 350 fpm. Check with and without the filters.

so until you have the tools, what can you do... caveman testing!!!!

first off, get a feel for how much air is pumping out of the registers upstairs. just use your hand or tie a piece of yarn to the registers (i use yarn, med weight, 1 foot and some tape.) run the system and see how far the yarn moves. Now remove all the upstairs registers. run the system and feel for any difference. Re-tape the yarn if thats how you are checking. My guess is that you will find a larger volume of air moving through the opening. All registers are not created equal!!! some are restrictive and some are not.

next, with the registers off, remove all the filters in all the returns. run the system and check the air flow up stairs again. My guess is that it will be much better.

shut down the system and open up the air handler service door and take a look at the evap coil. Is it clean or dirty (dust hair etc). Now run the system with the doors open (there may be a switch that will not allow this, defeat that switch). Re-check the upper floors. My guess is that you will have more air flow.

so what have we found???? my guess is that you do not have enough returns and your registers are restrictive and maybe your coil is dirty. My guess is also that your delta t is high, due to static pressure or low air flow.

How to fix it?????

1. caulk around the registers. This will stop any air from leaking into the walls/ floors. Mastic the seams of the ducts, as far as you can reach. this will help (in a small part) to keep the air in the ducts. its easy to do and since you have the registers open anyway!!! just do it!!

2. mastic up the return seams and into the return as far as possible..same thing as above.

3. Research better flowing registers. replace the upper floors. I have found that registers with flow dampers are not so good. Adjustable bar type registers are good. None of them are cheap!!!

4. research air filters. retrofit your system with 5 inch media filters.

I think (4000 miles away), you will find some improvement with these suggestions.

but get the tools and check yourself!!! After the air flow issues are fixed, read up on subcool and superheat in order to be educated when you call a professional to check your system for refrigerant levels!!!

good luck and report back what you find!!!!!

Last edited by bobinphx; 07-24-2012 at 10:09 AM. Reason: oopppps
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Old 07-24-2012, 01:24 PM   #14
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For all the HVAC experts! 2 level difference


The problem is you need more btu's and air flow as you go up in levels of your home in summer and less btu's as you go up in winter. the ductwork will only deliver a set amount regarless of what you the load is. You can check deltal T but too much air flow will not reduce the deltal T. to little air flow will increase the delta t and will freeze the coil. My opinion as a HVAC contractor in your near your vary area.

If you were only cooling or only heating through these ducts you could address sizing to correct the problem. your main problem is you need different amount of Btu 's foor cooling than you do for heating.
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Old 07-24-2012, 02:14 PM   #15
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For all the HVAC experts! 2 level difference


thank you so much for the input Bob from 4000 miles away! i am going to try to do some caveman testing here. i think you are right its more a flow issue than anything else because downstairs its fine.

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