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 02-28-2013, 04:10 AM   #121
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,109
Rewards Points: 118
Share |
Default

Will the size of my ducts have to be changed?


Your Summer grains of moisture is 84, so your not in a dry climate. A 2 ton unit will still just meet your sensible loss. You can use a 50,000 BTU 80% furnace. Or a 40,000 BTU 95% efficient furnace.

beenthere is online now   Reply With Quote
Old 02-28-2013, 04:56 AM   #122
Member
 
Join Date: Jul 2011
Location: Houston Texas
Posts: 1,080
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
I increased that outdoor Summer Temperature on the Manual J program to 86 degrees and it still showed I should use a 2 ton unit. When I increased it to 88 degrees it went to a 2.5 ton unit. I think 2 ton is looking like my choice. What do you think guys?

The Total Heat Loss is 37,849 BTUH. The program says to add 20% to that for a total of 45,419 BTUH. Do they round these amounts to 50,000?

My 1975 heating unit is rated at 100,000 BTUH (input) and 80,000 BTUH bonnet capacity. Of course the house had single pane windows,very little insulation from day one. The house was built in 1965 and this heater says 1975 on it. Maybe the original heater was rated lower and they purchased a larger one or maybe the original one took a dump. Maybe when they bought a new one they told them they wanted a larger one because the original one was not getting it done or the installer sold them a larger one.
My heater is over 30 plus years and it works okay but now I am going from a 100,000 BTUH / 80,000 bonnet capacity to a recommendation of 45,419 BTUH. Is that possible?
Again, as one homeowner to another, I go back to the scenario I had. Although they claimned 3 ton in my home was adequate, I found that the high summer temp they used wass not realistic and the lessor 3 ton just ok.

Reminds me of software for a computer, it says on the box a "suggested" minimum computer spec for software use. But if you stay with the minimum, it will work but be slow. If you increase, obviously it works better.

I read back thru this and I believe that on at least 2 times, BT has suggested that 2 tons would just barely be enough.

You have to make the decision: do you go 2 tons knowing that if you go out of your design temps in summer, that your unit may run a long time with minor impact. Or do you go to 2.5 knowing that you will be comfortable all of the time.

Me, I am going with the 2.5!
__________________
digitalplumber is just a name for use here, I am not a plumber!
digitalplumber is offline   Reply With Quote
Old 02-28-2013, 10:30 AM   #123
Member
 
Join Date: Mar 2008
Location: Orange County,California
Posts: 271
Rewards Points: 0
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by beenthere View Post
Your Summer grains of moisture is 84, so your not in a dry climate. A 2 ton unit will still just meet your sensible loss. You can use a 50,000 BTU 80% furnace. Or a 40,000 BTU 95% efficient furnace.
1.) Is the 50,000 BTU 80% furnace the same type I am using now?

2.) Would you explain the 95% efficient furnace? It sounds like I am getting less loss of heat with this style.

3.) Would you recommend one over the other? Pros/Cons

- is one clearly better than the other?
- price?
- anything else?
Pawl is offline   Reply With Quote
Old 02-28-2013, 10:37 AM   #124
Member
 
Join Date: Jul 2011
Location: Houston Texas
Posts: 1,080
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
1.) Is the 50,000 BTU 80% furnace the same type I am using now?

2.) Would you explain the 95% efficient furnace? It sounds like I am getting less loss of heat with this style.

3.) Would you recommend one over the other? Pros/Cons

- is one clearly better than the other?
- price?
- anything else?

The more efficient, the better the unit will be, but you will pay more initially for the furnace. I personally would not install anything less than 90%.

I would assume that if you bought another new funace the same as you had now lets just say a 50K @ 80%, the only difference would be technology on the mainboard and motor, but efficiency would be the same.

Then again, if you hardly use it the added cost to the higher efficiency may not be worth it.
__________________
digitalplumber is just a name for use here, I am not a plumber!
digitalplumber is offline   Reply With Quote
Old 02-28-2013, 11:15 AM   #125
Member
 
Join Date: Jan 2013
Posts: 144
Rewards Points: 0
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
1.) Is the 50,000 BTU 80% furnace the same type I am using now?
It looks to me like an 80% just by calculating input capacity vs. bonnet capacity.

Quote:
2.) Would you explain the 95% efficient furnace? It sounds like I am getting less loss of heat with this style.
Correct the effieciency of a gas furnace is figured simply by what percentage of the heat created goes in your house vs. what percentage goes out the flue pipe. So if your furnace makes 100,000 btu's but 80,000 btu's go into the house then the efficiency is 80%

Quote:
3.) Would you recommend one over the other? Pros/Cons

- is one clearly better than the other?
- price?
- anything else?
Well higher efficiency is obviously better, but there are some things to watch out for with the higher end units. For instance if you go 95% they usually use a variable speed blower, this causes the unit to usually run quieter, but if the motor goes out they are quite expensive to replace. And the savings you get by choosing 95% vs. a lower end 90% unit (usually they aren't exactly 90% usually around 92%) doesn't pay back very quickly because the units cost quite a bit more. Then if you have an expensive motor go out you've spent what savings you did make replacing the motor.

IMO I'd just go with a lower end 90% unit which will get you the savings but not be much more expensive to purchase than the 80% without paying big bucks for the 95%. In other words you get more bang for your buck with a lower end 90% again IMO.

Also if you're getting a new A/C anyway I would recommend looking at a heat pump. It's basically the same as an A/C with some extra parts which allow it to make heat and it makes heat much cheaper than gas or electric. The cost difference from a A/C to a Heat Pump is usually only about $500.
JScotty is offline   Reply With Quote
Old 02-28-2013, 11:45 AM   #126
Member
 
Join Date: Mar 2008
Location: Orange County,California
Posts: 271
Rewards Points: 0
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Again, as one homeowner to another, I go back to the scenario I had. Although they claimned 3 ton in my home was adequate, I found that the high summer temp they used wass not realistic and the lessor 3 ton just ok.

Reminds me of software for a computer, it says on the box a "suggested" minimum computer spec for software use. But if you stay with the minimum, it will work but be slow. If you increase, obviously it works better.

I read back thru this and I believe that on at least 2 times, BT has suggested that 2 tons would just barely be enough.

You have to make the decision: do you go 2 tons knowing that if you go out of your design temps in summer, that your unit may run a long time with minor impact. Or do you go to 2.5 knowing that you will be comfortable all of the time.

Me, I am going with the 2.5!
I remember BT said, "a 10 degree increase in outdoor summer design temp would easily increase size of ac unit by 1/2 ton".

I went from 86 degrees with a 2 ton unit recommendation and then put 88 degrees in my outdoor summer design temp and it increased the recommendation to 2.5 ton. So regarding my load calculations if 88 degrees is the low end temperature of going from 2 to 2.5 tons and if what BT is saying is true here in the 1st sentence of my response then theoretically I have a 10 degree cushion for days over 88 degrees. In 2012 my area had 5-89 degree days, 2 days of 90, 91-1x, 92-3x, 94-2x, 96-2x,102 once. Does what I am saying sound right?

Regarding the last paragragh above when I left window coverings and shading out of the program it increased 9000 BTUHs under the Total Heat Gain column. Meaning when those windows are covered on really hot days and with a 9000 BTUH reduction in Total Heat Gain the 2.5 ton unit should keep me comfortable all the time and not have to run a long time with low impact. Sound right?

Last edited by Pawl; 02-28-2013 at 12:26 PM.
Pawl is offline   Reply With Quote
Old 02-28-2013, 11:55 AM   #127
Member
 
Join Date: Mar 2008
Location: Orange County,California
Posts: 271
Rewards Points: 0
Default

Will the size of my ducts have to be changed?


BT - will this information you mentioned on an earlier post apply to my 1000 cfm breakdown below? ------> The duct system should be designed for the full 400 CFM per ton (1000CFM for a 2.5), and then the blower set to only move 350 CFM per ton(875CFM). The installers should balance it out to each rooms needs then. With any excess air being equally allotted to each room.
Attached Thumbnails
Will the size of my ducts have to be changed?-house-floor-plans-030.jpg  

Last edited by Pawl; 02-28-2013 at 12:30 PM.
Pawl is offline   Reply With Quote
Old 02-28-2013, 03:10 PM   #128
Member
 
Join Date: Jul 2011
Location: Houston Texas
Posts: 1,080
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
BT - will this information you mentioned on an earlier post apply to my 1000 cfm breakdown below? ------> The duct system should be designed for the full 400 CFM per ton (1000CFM for a 2.5), and then the blower set to only move 350 CFM per ton(875CFM). The installers should balance it out to each rooms needs then. With any excess air being equally allotted to each room.

Puzzled here as to how an upstairs bedroom can require more heat CFM than cooling?
__________________
digitalplumber is just a name for use here, I am not a plumber!
digitalplumber is offline   Reply With Quote
Old 02-28-2013, 03:13 PM   #129
Member
 
Join Date: Jul 2011
Location: Houston Texas
Posts: 1,080
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
I remember BT said, "a 10 degree increase in outdoor summer design temp would easily increase size of ac unit by 1/2 ton".

I went from 86 degrees with a 2 ton unit recommendation and then put 88 degrees in my outdoor summer design temp and it increased the recommendation to 2.5 ton. So regarding my load calculations if 88 degrees is the low end temperature of going from 2 to 2.5 tons and if what BT is saying is true here in the 1st sentence of my response then theoretically I have a 10 degree cushion for days over 88 degrees. In 2012 my area had 5-89 degree days, 2 days of 90, 91-1x, 92-3x, 94-2x, 96-2x,102 once. Does what I am saying sound right?

Regarding the last paragragh above when I left window coverings and shading out of the program it increased 9000 BTUHs under the Total Heat Gain column. Meaning when those windows are covered on really hot days and with a 9000 BTUH reduction in Total Heat Gain the 2.5 ton unit should keep me comfortable all the time and not have to run a long time with low impact. Sound right?

Unless you need to pinch pennies and role the dice for non extreme hot days, I would do the 2.5 and be done with it. All of this stuff is "in theory" and could be you install 2.5 tons and have a record heat season!
__________________
digitalplumber is just a name for use here, I am not a plumber!
digitalplumber is offline   Reply With Quote
Old 02-28-2013, 03:39 PM   #130
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,109
Rewards Points: 118
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Unless you need to pinch pennies and role the dice for non extreme hot days, I would do the 2.5 and be done with it. All of this stuff is "in theory" and could be you install 2.5 tons and have a record heat season!
Yep, he could have a record heat season that it can't keep up. no big deal, cause that type of heat wouldn't occur again for 20, 50 or 100 years. you can't plan for the absolute worse extremes, and then have an economical running system.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
digitalplumber (02-28-2013)
Old 02-28-2013, 03:40 PM   #131
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,109
Rewards Points: 118
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Puzzled here as to how an upstairs bedroom can require more heat CFM than cooling?
If it has a fair amount more windows then the other rooms, and faces east.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
digitalplumber (02-28-2013)
Old 02-28-2013, 03:42 PM   #132
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,109
Rewards Points: 118
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
BT - will this information you mentioned on an earlier post apply to my 1000 cfm breakdown below? ------> The duct system should be designed for the full 400 CFM per ton (1000CFM for a 2.5), and then the blower set to only move 350 CFM per ton(875CFM). The installers should balance it out to each rooms needs then. With any excess air being equally allotted to each room.
Basically yes. You'll find the second floor landing actually needs 50% more air then the program will say. Unless its a landing with a door at the bottom of the steps to prevent heat from the first floor rising.
beenthere is online now   Reply With Quote
Old 02-28-2013, 04:36 PM   #133
Member
 
Join Date: Mar 2008
Location: Orange County,California
Posts: 271
Rewards Points: 0
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Puzzled here as to how an upstairs bedroom can require more heat CFM than cooling?
That one upstairs bedroom window is 8' wide by 34" tall with full southern exposure all day long. Only window in the whole house with full exposure to sun all day. Plus I did not take any credit for window coverings. That is my biggest window.
Pawl is offline   Reply With Quote
Old 02-28-2013, 04:42 PM   #134
Member
 
Join Date: Jul 2011
Location: Houston Texas
Posts: 1,080
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
That one upstairs bedroom window is 8' wide by 34" tall with full southern exposure all day long. Only window in the whole house with full exposure to sun all day. Plus I did not take any credit for window coverings. That is my biggest window.

Window Tint!
__________________
digitalplumber is just a name for use here, I am not a plumber!
digitalplumber is offline   Reply With Quote
Old 02-28-2013, 05:14 PM   #135
Member
 
Join Date: Dec 2008
Location: Las Vegas, NV
Posts: 445
Rewards Points: 4
Default

Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Window Tint!
Gotta be careful with window tint. My wife spent a fortune in tinting our front west facing windows, only to find the glass got much hotter.
I peeled the tint and went back in with new solar screens.

Maybe there are other types of tint that would be a better choice but for us, we tried two different kinds and they both doubled window temps.

sammy37 is offline   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
Wiring Size Calculations for New Service CorinthWest Electrical 7 12-07-2010 11:36 AM
Room size X floor tile size deck hand Flooring 4 04-08-2009 04:42 PM
hard metal vs. flexible ducts katea HVAC 4 05-18-2008 08:23 AM
Wire size and Breaker size for remodel ?? Skydmark1 Electrical 12 12-15-2007 05:00 PM
Rehab Mess- Ducts Knocking-Furnace Vibrating drmark7 HVAC 7 03-18-2007 04:34 PM




Top of Page | View New Posts

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