Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 11-15-2010, 05:39 PM   #16
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 9,628
Rewards Points: 2,394
Default

Manifold pressure setting on new furnace


Manometers if properly taken care of in a padded case and not bounced around loose in a service truck should stay accurate. Few guys own a water tube one/ I don't but they are the most accurate. I would be a bit uncomfortable with their attitude and the way they setup your expensive furnace now. May want to get a 2nd reliable co to check it out later. It is a very complex procedure to check temp rises/adjust blower and I would meter clock it on all 3 stages to make sure it is not overfiring. There is a special procedure in the Trane manual for setting the manifold pressure and I hope they follow it.

__________________
"Cut it twice and it is still too short".
yuri is online now   Reply With Quote
Old 11-15-2010, 06:03 PM   #17
Member
 
Join Date: Aug 2008
Posts: 131
Rewards Points: 75
Default

Manifold pressure setting on new furnace


The furnace is a XV95 two stage unit 100K BTU at 95% efficiency. The service data indicates that first stage heating with blower on Medium Low the CFM is 971, temp rise is 58 at 0.1 static pressure. Second stage is 1464 CFM, temp rise is 59 at 0.1 static pressure. These numbers are probably based on the recommended manifold pressure of 3.5 and since mine is set at 4.0 I don't know what the temperature rise is on either stage of heat but we are going to find out in the morning.
Changing the blower setting to Medium would increase the CFM to 1146 with temp rise of 49 in first stage and CFM to 1631 with temp rise of 53 in second stage. FYI, the Medium speed is factory setting so they must have changed the blower setting while adjusting the furnace during the install. The temperature rise range for this furnace is 35-65.
Beenthere - Is this what you were asking for in your previous post?
kb3ca is offline   Reply With Quote
Old 11-15-2010, 06:10 PM   #18
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,576
Rewards Points: 2,832
Default

Manifold pressure setting on new furnace


Yes.

Trust me. Your furnace is operating against a lot more then a .1" static pressure.

Your air filter. Even if it is a cheap see through fiberglass one, will have a PD of .07" min.
Your supply registers will have a min of .03" PD. And your return grille will also have a min of .03" PD.

Thats .13" static, and I didn't include any of the duct work yet. Or an A/C coil, if you have A/C on the furnace.
beenthere is online now   Reply With Quote
Old 11-15-2010, 06:24 PM   #19
Member
 
Join Date: Aug 2008
Posts: 131
Rewards Points: 75
Default

Manifold pressure setting on new furnace


Yes, it does have an A/C coil. I just gave you the first set of figures listed for static 0.1 to give you an idea of the difference between MediumLow and Medium blower settings. It does list CFM and temperature rise for static pressures of 0.1, 0.3, 0.5, 0.7, and 0.9.
Since they set the manifold pressure to 4.0 I would think that the temperature rise at any given static pressure would be greater. So, why would they lower the blower speed to med/lo instead of leaving it at the factory setting of Medium?
Should I set the blower to the factory setting?
kb3ca is offline   Reply With Quote
Old 11-16-2010, 02:04 AM   #20
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,576
Rewards Points: 2,832
Default

Manifold pressure setting on new furnace


Quote:
Originally Posted by kb3ca View Post
Yes, it does have an A/C coil. I just gave you the first set of figures listed for static 0.1 to give you an idea of the difference between MediumLow and Medium blower settings. It does list CFM and temperature rise for static pressures of 0.1, 0.3, 0.5, 0.7, and 0.9.
Since they set the manifold pressure to 4.0 I would think that the temperature rise at any given static pressure would be greater. So, why would they lower the blower speed to med/lo instead of leaving it at the factory setting of Medium?
Should I set the blower to the factory setting?
Need to check actual temp rise first.

Might want to wait until they reset the manifold pressure back to 3.5" then see what temp rise is and adjust it then if need be.
beenthere is online now   Reply With Quote
Old 11-16-2010, 10:55 AM   #21
Member
 
Join Date: Aug 2008
Posts: 131
Rewards Points: 75
Default

Manifold pressure setting on new furnace


My HVAC guy came this morning to replace the O.D. sensor and to check out my furnace manifold pressure. While he was here I had him check the starting and running amps on the XL15i condenser because I suspected it was drawing a lot more power when running in the heat mode versus the cooling. The starting amps in heat mode were 25 and running amps were 12.5 which is well within the specs for the unit. He did a manual defrost and the running amps were 9.0 without the condenser fan running and it is rated at 2.8 amps so looks like all is well with the heat pump.
Next, I had him check the manifold pressure and temperature rise on the XV95 two stage furnace. Manifold pressure in first stage was 1.2" and second stage was 3.3" which is within specs for this furnace. He said his gage reads a little low. The temperature rise in stage two was 60 degrees. The range for this furnace is 35-65 degrees and I thought it was a little too close to the upper limit so I had him change the dip switches on the blower to run on Medium speed which is the factory setting instead of MedLow which it was set to during installation. After increasing the blower speed the temperature rise was 47 degrees and I'm leaving it there for now. Air temperature out of the registers is nice and warm and everything seems to be set up correctly.
Want to offer my sincere thanks to all who responded to my post and provided good advice on this matter. I feel good now that I have confirmed that everything is operating properly.
kb3ca is offline   Reply With Quote
Old 11-16-2010, 05:00 PM   #22
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,576
Rewards Points: 2,832
Default

Manifold pressure setting on new furnace


Glad you recognized that 60 was too close to the upper limit.

I shouldn't say this. it might make you wonder too much. But. I wonder how he knows his gauge reads a little low. And how he knows how low a little low is. To know if your manifold is set right.

Next year. When you have it serviced. make sure the tech uses an accurate manometer to check it.

beenthere is online now   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Goodman gas furnace getting 3 flashes, stuck pressure switch chuck2009 HVAC 4 11-02-2010 11:42 PM
hi pressure in the furnace TonyQ Plumbing 2 10-28-2010 08:46 AM
Pressure on the furnace azdcoast HVAC 3 10-05-2010 05:54 PM
Pressure Switch, Draft Inducer, Burner Box, Problem majorapus HVAC 7 10-25-2009 06:14 PM
furnace pressure switch Mike T. HVAC 3 10-10-2009 01:26 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.