As I had brought up years ago, ACCA's Manual S was in dire need of an update.  Written in 1995, Manual S Residential Equipment Selection was passed by with huge technical and efficiency strides within the HVAC industry.  Think about it: ECM Motors were in their infancy, condensing furnaces were still prone to failures, and variable refrigerant flow was far from mainstream in the U.S.  All addressed in the updated Manual S! I have to say, their committee did a thorough job addressing updates to a process that is essential to system design and a code requirement in most of our country!  I highly recommend HVAC Sales Staff, System Designers, and Building Analysts purchase a copy of the new text, but in the meantime here is a teaser:

1.  Multi-Stage Central A/C: can be sized between .90 and 1.20 of the total building load.  This additional 5% of capacity vs. 1995 becomes increasingly important as homes get tighter and Sensible Heat Ratios rise.  Higher airflow to handle the increase in sensible loads lends to higher capacities.

2.  Variable Capacity Central A/C: can be sized between .90 and 1.30 of the total load.  See #1 for sensible capacity reasons, but variable capacity equipment is great for handling high latent capacities when operating on part load days as well.

3.  Cold Climate Heat-Pumps: can be sized to the total cooling building load + 15,000 btu/hr maximum.  This goes for single-stage, two-stage, and variable capacity equipment.  For mini-split heat-pumps, this 15K is above the total block load.

4.  Heat Pump Supplemental Electric Heaters: can be no larger than 5KW if the heat load is < 15,000 btu/hr.

5.  Fossil Fuel Burning Furnaces and Boilers: can be sized between 1.0 and 1.40 of the total heat load.  Ok, this isn't a change, just thought it was important to know!  If installing a furnace that needs a larger blower for cooling, maximum is now 2.0.

     Loaded with up to date examples, the new Manual S is far from a dust collector.  A great reference manual, but lets just hope it is not for another two decades like it's predecessor...but don't take my word for it!

Excess Air

Views: 138


You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Eric Kjelshus on August 28, 2014 at 8:33am

I run loads each day.  BUT my completion does not,    I see so much over sizing  last job was needing 34,000 and he put in 120,000 BTU's ( the box fit)  I took out 1/2 the burners so the BTU fit the duct work and closer to the building.    My grand Pa would size 3 times needed or down to -40  so you could open the windows in bedrooms 8" to get "air" at night.   in the 1880 the gas was made from coal and was very high CO  when would burn,  some  Lights would be gas and CO in the building go high so would open window's to vent the home.    Gas was so cheap that was not metered  just so much a yr.

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Profile IconDenise Cooper, Maren Cooke, Steven Antonini and 1 more joined Home Energy Pros
15 hours ago
Crosbey Archery joined Allison A. Bailes III's group


HVAC design, Manuals J, S, T, & D, Duct leakage, Air flow, ENERGY STAR new home requirements,…See More
22 hours ago
Crosbey Archery commented on Ottawa Furnace Filters's blog post Some Useful Information about Furnace Air Filters
"This post is really helpful especially to those homeowners who are still confused on what to…"
23 hours ago
Diane Chojnowski posted videos
Diane Chojnowski posted a discussion

Incentives & financing options for home energy upgrades has a useful database of incentives and financing options for home energy efficiency…See More
George Kopf commented on Home Energy Magazine's blog post My Fall Into The Smart Home, Lazy Life
"Matt, Another way of looking at this is that by freeing up my time/brain power, I can give more…"
Chris Laumer-Giddens's blog post was featured

Sparky Doubled the Air Leakage in this Home!

Sparky Doubled the Air Leakage in this HomeThis is the home.This is the hole that Sparky…See More
Chris Laumer-Giddens posted a blog post

Sparky Doubled the Air Leakage in this Home!

Sparky Doubled the Air Leakage in this HomeThis is the home.This is the hole that Sparky…See More

© 2015   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service