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Old 07-01-2009, 01:06 PM   #1
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ac size versus ventilation and RA


I have an 1800 ft 2 story home, 1100main floor, 700 ft with 3 BR upper, 1100 ft open basement, brick main level with stucco upper 2 x4 construction, 35 years old unfinsihed basement. R13 insulation in upper levels, R 19 in attic, soon to be R50

Replaced furnace withn HE Carrier this winter.Heating was vastly improved and more comfortable.
AC unit is an original Sears C875-47051-1 but I dont see any specs on output on the labelAc is blowing cool but I want to improve the current system as the upper level does not cool well and basement is frigid.

Need to know :

what humidity setting is best for summer
what fan speed or is auto best AC function on programmable Carrier Infinity Controller for summer and AC

I have 3 RA vents on Main floor,2 upstairs in 2 of 3 bedrooms,all approx 16 x 8 but none in basement. Planning on adding 5 new RA at ceiling with dampers at floor level in upper levels. Should the basement have one as well ,or more than one as I add dividing walls

Basement has remained extremely cool with poor air flow to top floor

What other info do I need to post to determine how to maximise the AC
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Old 07-01-2009, 01:42 PM   #2
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ac size versus ventilation and RA


Basements in our cold climate tend to always be cold and I put electric baseboard heaters in mine. I will not reduce my air circulation upstairs by sucking part of it RA from the basement. I do a lot of custom work/balancing ductwork and I would recommend this procedure. Buy yourself an rotating vane anemometer and check the airflow in fps from all your supply vents and draw a map of them and record the readings. Then throttle down some of the lower ones to boost the airflow upstairs. Your ECM motor will compensate for what you do and maintain static pressure and flow. The results have to feel good and no facts or figures from the internet will solve your problem. http://www.trutechtools.com/cart/ind...products_id=44
You can get smaller versions for around $200. If you know someone in the biz get them to buy it at WWG Totaline. Unfortunately they only sell to contractors now.
Happy Canada Day!!

Last edited by yuri; 07-01-2009 at 01:55 PM.
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Old 07-01-2009, 02:00 PM   #3
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ac size versus ventilation and RA


Thanks Yuri,

Should I maintain equal RA vent size at the ceiling?

Enjoy your Canada Day. Do they have firewoks at the Forks now?
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Old 07-01-2009, 02:05 PM   #4
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ac size versus ventilation and RA


I don't do duct sizing but Beenthere sounds good at it. We have fireworks and they are building this huge Museum of Human Rights there now. First Federal funded major museum outside of Ottawa. Should be real interesting when done in a couple years:http://www.canadianmuseumforhumanrights.com/

Last edited by yuri; 07-01-2009 at 02:10 PM.
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Old 07-01-2009, 02:17 PM   #5
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ac size versus ventilation and RA


I forgot, this is the Canuck hotline today. BT is likely still at work.

Good to see some Fed Money outside the Capital, I'm surprised all the streets aren't cobblestone.Ottawa is one beautiful city but talk about seeing your tax dollars at work....

The Forks is shaping up nicely 20 years too late for me but I still go back to visit and feed the mosquitos
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Old 07-01-2009, 02:32 PM   #6
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ac size versus ventilation and RA


Your return grilles should be larger then your supply grilles.
You don't want noise from returns. So they should be larger.

Ideal return grilles would only have a velocity of 300FPM.
Since its hard to live in an Ideal world. Try to size them between 300 and 400FPM face velocity.
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Old 07-01-2009, 02:48 PM   #7
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ac size versus ventilation and RA


Hey BT Thanks.

Do I need Yuri's GIZMO to calculate my FPM?
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Old 07-01-2009, 02:54 PM   #8
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ac size versus ventilation and RA


That, or you can buy a duel pressure manometer pitot tubes and transition the ducts.
Cost is about the same, but, its much easier to use a vanemanometer.
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Old 07-01-2009, 03:15 PM   #9
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ac size versus ventilation and RA


And more FUN!!
I make lots of $$ doing specialty jobs with mine. Plus tweaking the blower adjust settings on the board can get you +/- 15% air on the G71.
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Old 07-01-2009, 03:27 PM   #10
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ac size versus ventilation and RA


LOL, yea, its hard to find a 6' straight peice of duct, with no take offs in it. Or els interfering.
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