Home Page link

Does duct size really matter when using ECM2 motor?

Home| Search | About
Login Password
Register Now! Lost Password?

HVAC Discussions - Heating, ventilation and air conditioning. 

Page 3 of 6       < 1 2 3 > last >> Bookmark this page:  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
Does duct size really matter when using ECM2 motor? Double A-Ron 01-19-2007
If you were  Registered and logged in, you could reply and use other advanced thread options
Posted by on January 20, 2007, 7:00 pm
"Double A-Ron" wrote:


>
>When it was suggested "someone who knows distribution systems" is this
>referring to another HVAC technician or an Engineer? What do I look for
>in the Yellow pages?

forget the yellow pages....see below

>
>Was that one 20 x 16 duct for supply and another 20 x 16 for return?

yup. total airflow in the supply typically = total airflow in the
return. sometimes the return can be decreased by 10% if there is that
much fresh air being brought in thru a dedicated duct from the great
outdoors. 20% or more on commercial systems.


>
>I'd prefer to have the duct system designed and do the work myself as I
>have full access to duct work...... and no money.

no problem. all you need to do is obtain a copy of ACCA Manual D
Residential Duct Systems. Read it until you comprehend what it is
saying, and then proceed. remember, this is not rocket science.
anybody that can read & comprehend english can do this work.
errrr well most everybody.....

http://cgi.ebay.com/Residential-Duct-Systems-Manual-D-BOOK-ACCA-ANSI_W0QQitemZ270080735569QQihZ017QQcategoryZ2228QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


>
>I'm still puzzled why the furnace has only a 14"x14" supply duct;
>however it suggested I'll need a 20" x 16"?

nobody can see your system except you. I have no idea what you need.
However, if I want to move 1950 cfm at .08" w.c., I will need a 16x20
duct to do so. Actually a 15x20, but I like even numbers.

why is it 14 x 14? which is cheaper to build? who got to do the
original install? the lowest bidder. now you know.

AppliancePartsPros.com, Inc.
Posted by Double A-Ron on January 21, 2007, 8:41 am
Thanks Gone Fishing.... you really gave me hope! I'll order manual D
today.

You can see what I mean about the 14"x14" supply duct in the
Waterfurnace manual, page 13, here's a direct link:

http://www.waterfurnace.com/Envision/pdf/SP1585.pdf

-        horizontal model 060-070
-        discharge connection "M" - 13.6"
-        discharge connection "N" - 13.2"

FYI, here's a very user-friendly Design Heat Loss program that does
duct sizing too;

http://www.hvaccomputer.com

In the mean time I'd like to increase my 4 air return vents by removing
some drywall to open up the holes. Can you kindly suggest the grill
sizes required keeping in mind I'll increase the actual return ducting
in the near future.

Thanks again for your help, I'd really like to but ya some beers.


gofish@gonefishin.net wrote:
> "Double A-Ron" wrote:
>
>
> >
> >When it was suggested "someone who knows distribution systems" is this
> >referring to another HVAC technician or an Engineer? What do I look for
> >in the Yellow pages?
>
> forget the yellow pages....see below
>
> >
> >Was that one 20 x 16 duct for supply and another 20 x 16 for return?
>
> yup. total airflow in the supply typically = total airflow in the
> return. sometimes the return can be decreased by 10% if there is that
> much fresh air being brought in thru a dedicated duct from the great
> outdoors. 20% or more on commercial systems.
>
>
> >
> >I'd prefer to have the duct system designed and do the work myself as I
> >have full access to duct work...... and no money.
>
> no problem. all you need to do is obtain a copy of ACCA Manual D
> Residential Duct Systems. Read it until you comprehend what it is
> saying, and then proceed. remember, this is not rocket science.
> anybody that can read & comprehend english can do this work.
> errrr well most everybody.....
>
>
http://cgi.ebay.com/Residential-Duct-Systems-Manual-D-BOOK-ACCA-ANSI_W0QQitemZ270080735569QQihZ017QQcategoryZ2228QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
>
>
> >
> >I'm still puzzled why the furnace has only a 14"x14" supply duct;
> >however it suggested I'll need a 20" x 16"?
>
> nobody can see your system except you. I have no idea what you need.
> However, if I want to move 1950 cfm at .08" w.c., I will need a 16x20
> duct to do so. Actually a 15x20, but I like even numbers.
>
> why is it 14 x 14? which is cheaper to build? who got to do the
> original install? the lowest bidder. now you know.


Posted by on January 21, 2007, 12:40 pm
"Double A-Ron" wrote:


>You can see what I mean about the 14"x14" supply duct in the
>Waterfurnace manual, page 13, here's a direct link:
>
>http://www.waterfurnace.com/Envision/pdf/SP1585.pdf
>
>-        horizontal model 060-070
>-        discharge connection "M" - 13.6"
>-        discharge connection "N" - 13.2"

what you're looking at on that page is the discharge opening of the
blower. the airhandler is rated at 5-6 tons, so consequentially, yes,
it will have a discharge of that size, based soley on the blower
wheel. Notice the return air opening size? Ideally your supply duct
would be somewhat similiar, based on the total cfm YOUR system is
supposed to be delivering. If you maintain only the 14x14 supply
duct, the static pressure inside will be such that it limits the
ability of the blower to deliver the correct airflow, plus it will
cost you $$ in operational costs.

My ductulator says at 1950 cfm a 14x14 duct by itself will impose a
.2" w.c. static pressure on the blower. Now factor in all the other
restrictions like filter, coil, & too small return ducting. You ARE
NOT getting the engineered airflow the manufacturer of your equipment
recommends. It cannot perform to factory specs.

>
>FYI, here's a very user-friendly Design Heat Loss program that does
>duct sizing too;
>
>http://www.hvaccomputer.com


I learned correct duct sizing long before there were computer
programs. Computer programs exist so people dont have to learn the
basics. Any moron can use a program to plug in numbers. Computer
programs that are based on ACCA Manual J & D are approved by city
building departments. I would strongly question software that wasnt
approved.

You dont need software if you can read and comprehend ACCA Manual D.

FWIW, the ONLY software I would recommend is
http://www.wrightsoft.com/overview/unitedstates/default.asp?country=US


>In the mean time I'd like to increase my 4 air return vents by removing
>some drywall to open up the holes. Can you kindly suggest the grill
>sizes required keeping in mind I'll increase the actual return ducting
>in the near future.

yes. install 4 each 14x20 bar type commercial grade return grills.
From these run 4 12" dia ducts back to the air handler. The 14" is
width, they will fit inbetween the 16" on center wall studs. The 20"
is the vertical height. The 14x20 bar type grill will have the bars
running horizontally, parallel with the floor.

>
>Thanks again for your help, I'd really like to but ya some beers.
>

screw the beers, I drink Drambuie straight up.

Posted by GoUP on January 21, 2007, 2:04 pm

> FWIW, the ONLY software I would recommend is
> http://www.wrightsoft.com/overview/unitedstates/default.asp?country=US
>
>

IF all the parameters are set up correctly.... I've found many quotes that
didn't have the numbers right...

The old rule of thumb for residential has always worked. Cheap customer .1"
Customer who desires quiet, comfort and quality .08"

However, on a two stage system such as Waterfurnace, if you use too large a
duct you better make sure your spread and throws on your registers are
matched also for the lower CFM if wall or ceiling mounted. Also, the larger
duct should be insulated or the end of the line will have cooler air coming
out. I like to keep my velocities up a little on two stage units which
allow me to use registers to match the low and high limits of the design. I
have gone as high as .13" depending on the size of the low stage for AC
verses the high side heat output.

Now, in defense of the contractor, Waterfurnace and everyone else who is a
supplier has told me the exact same thing, "Don't worry about the duct size,
the ECM motor will overcome the resistance." I've heard this at least a
dozen times from Trane, American Standard, FHP, ClimateMaster, WaterFurnace,
Rheem, Rudd and ComfortAir. They are right up to .15" but after that you
will definitely have problems.

My biggest concern for this customer is the cfm over the resistant heaters.
I'm sure if a performance/cfm check was done you would find your lacking and
getting very close to cycling on overloads. And, if they insulated the duct
near those heaters you may have a fire just around the corner.
I'm not trying to scare you, just telling you the truth. I never put
insulated duct within 2 feet of electric resistant heaters unless I make a
shield on the inside that has 1" clearance from the insulation. Just this
week we put two Waterfurnaces in. The outlet was 13.5 x 13.5 We had a duct
14" square by two feet lining the actual insulated duct of 18 x 18. The
radiant heat will not be allowed to start a fire this way. Even insulating
the outside has potential problems. I have seen a fan fall and catch
insulation on fire and burn out a canvas connector.

You need a whole house Manual J and Manual D performed. Let a competent
dealer do this for you. Tell him your coming back here to make sure his work
is right.




Posted by Steve Scott on January 21, 2007, 5:12 pm
I think you've misplaced your decimal points.


>
>> FWIW, the ONLY software I would recommend is
>> http://www.wrightsoft.com/overview/unitedstates/default.asp?country=US
>>
>>
>
>IF all the parameters are set up correctly.... I've found many quotes that
>didn't have the numbers right...
>
>The old rule of thumb for residential has always worked. Cheap customer .1"
>Customer who desires quiet, comfort and quality .08"
>
>However, on a two stage system such as Waterfurnace, if you use too large a
>duct you better make sure your spread and throws on your registers are
>matched also for the lower CFM if wall or ceiling mounted. Also, the larger
>duct should be insulated or the end of the line will have cooler air coming
>out. I like to keep my velocities up a little on two stage units which
>allow me to use registers to match the low and high limits of the design. I
>have gone as high as .13" depending on the size of the low stage for AC
>verses the high side heat output.
>
>Now, in defense of the contractor, Waterfurnace and everyone else who is a
>supplier has told me the exact same thing, "Don't worry about the duct size,
>the ECM motor will overcome the resistance." I've heard this at least a
>dozen times from Trane, American Standard, FHP, ClimateMaster, WaterFurnace,
>Rheem, Rudd and ComfortAir. They are right up to .15" but after that you
>will definitely have problems.
>
>My biggest concern for this customer is the cfm over the resistant heaters.
>I'm sure if a performance/cfm check was done you would find your lacking and
>getting very close to cycling on overloads. And, if they insulated the duct
>near those heaters you may have a fire just around the corner.
>I'm not trying to scare you, just telling you the truth. I never put
>insulated duct within 2 feet of electric resistant heaters unless I make a
>shield on the inside that has 1" clearance from the insulation. Just this
>week we put two Waterfurnaces in. The outlet was 13.5 x 13.5 We had a duct
>14" square by two feet lining the actual insulated duct of 18 x 18. The
>radiant heat will not be allowed to start a fire this way. Even insulating
>the outside has potential problems. I have seen a fan fall and catch
>insulation on fire and burn out a canvas connector.
>
>You need a whole house Manual J and Manual D performed. Let a competent
>dealer do this for you. Tell him your coming back here to make sure his work
>is right.
>
>


--
Mankind has been on a bad trip for a
long time now.





Page 3 of 6       < 1 2 3 > last >>
Similar ThreadsPosted
Grille Size vs Duct Size October 29, 2007, 9:55 am
How to determine return air duct size for a 50,000 BTU Gas Furnace September 19, 2006, 4:52 pm
Carrier variable speed motor, duct transitions - any problems? September 14, 2006, 4:01 pm
What size AC do i need? August 7, 2006, 6:21 pm
ac size June 7, 2007, 12:05 am
Size of A/C Unit July 1, 2006, 3:22 pm
compressor size? August 7, 2006, 11:30 am
Gas pipe size February 21, 2008, 5:18 pm
calculating capillary size February 14, 2007, 5:19 am
how contractors really size aircon October 5, 2007, 1:00 pm

Contact Us | Privacy Policy

XML SitemapXML Sitemap