FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Air temp at registers

user-100766 | Posted in Energy, Heating & Insulation on February 5, 2007 01:10am

I have a new house that is not sold yet and I am conserned about the furnace. It is a forced air 75k btu, propane fired, 80% efficient. The air coming out of the heat registers is only 89 degrees. Its a 2500 sq ft house and it took almost 50 minutes to raise the temp from 61 to 64. The outside temp was in the upper 40s. I checked the air temp at the register at another house I have, exact same temps, and it was 119 degrees at its highest temp and only took about 25 minutes. My home has a forced air NG furnace and it puts out about 114 degrees.

I talked to my heating contractor, he came and took a look and said that everything is working as it should and that it takes a while to raise the temp when its that low….bla bla.. I aint buyin it. Anyone out there that knows what the temp should be at the register with what I have dexcribed here? And any ideas what if anything could be wrong?? 

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. alwaysoverbudget | Feb 05, 2007 02:14am | #1

    first i  don't know craap about this,but  i thought you were suppose to get a 25 degree  over air temp.i'm guessing your house at 72 = 97 degrees,so that rule might not be right.the only time i have ever checked air temp it was with the air cond. on. larry

    hand me the chainsaw, i need to trim the casing just a hair.

  2. User avater
    rjw | Feb 05, 2007 02:23am | #2

    Check the manufacturer's plate, it should give temp rise range for the unit.


    With my mouth I will give great thanks to the Lord; I will praise Him in the midst of the throng. For He stands at the right hand of the needy, to save them from those who would condemn them to death.

    - Psalms 109:30-31

  3. MrBill | Feb 05, 2007 03:58am | #3

    Rusty,

     My furnace just turned on when I started reading this so .... stuck an HVAC thermometer in the register and its about 95 degrees. High efficiency Miller on Natural Gas. Outside air is about 30 degrees, thermostat is set at 68. 

    Any chance yours has the wrong gas jets in it ? I think propane is less efficient than nat gas ? Maybe the other way around, anyway I know that they need different jets to work properly.

     

     

    Bill Koustenis

    Advanced Automotive Machine

    Waldorf Md

    1. User avater
      rjw | Feb 06, 2007 03:09am | #8

      Plus, you have to calculate the delta of the return air to the "made" airThat's where the plate specs come in....

      With my mouth I will give great thanks to the Lord; I will praise Him in the midst of the throng. For He stands at the right hand of the needy, to save them from those who would condemn them to death.

      - Psalms 109:30-31

  4. Dave45 | Feb 05, 2007 04:13am | #4

    If you've just started running the furnace, it's gonna take a while to warm the house up.  Air is fairly easy to heat, but it takes time to get the walls warmed up.  Give it a couple of days to stabilize.

    Comparing the temperature at the registers between two houses doesn't mean much.  The heat loss between the furnace and the register will depend on the length of the heat duct, how well it's insulated, having good connections, etc. 

    If you can determine which registers have the shortest and longest duct runs, check their temperatures when the furnace is running.  You may need to partially close off the short run register to force more (warmer) air to the long run register.

    1. user-100766 | Feb 08, 2007 05:02am | #10

      Thanks for all the replies. Its a new house. Here we have to put R-22 in the walls, R-38 in the cieling and R- 30 in the floors. So the house is well insulated. I sided it and set all the windows and doors so I know there are no air leaks around any windows or doors. Also when I checked the temps  the furnace had been running in the house for about a month so it wasnt trying to warm a cold house. Everything in it should be at 61 to start with. Also the air temp coming from the duct was checked about every 10 minutes and 87 was the highest it got to. The furnace is a Rheem criterion. And yes it has been converted to LP. If you dont change the jets you get lots of black soot coming out the vent on the roof. (ask me how I know that).  Anyway it sounds like it may be within specks. I guess I am used to the furnace here in my  house that has the 114 degree air.  Thanks again for the help guys. I love this site.

  5. Grott | Feb 05, 2007 07:22pm | #5

    Just few things...

    If you do a heat loss calcualation you will be able to tell if the rating of the furnace is appropriate to your needs.

    To do a heat loss you will need to check the insulation values and materials, Size and U-value of windows and doors and the general "air tightness" of the home.

    Also are the ducts sealed, insulated? Are they in heated or un heated space? All these factors are important to your long term comfort.

    The air temp seems low to me, especially on an 80% unit. Most of those really bake the air.

    Garett

  6. DanH | Feb 05, 2007 08:37pm | #6

    When did you measure the air temp? You need to have the furnace running for several minutes before measuring. And fan speed makes a difference. The higher the fan speed the lower the output temp will be, even though the total heat output is a hair higher with the higher fan speed.

    In addition to timing temperature rise, time temperature drop. If it takes 50 minutes to raise the temp 3 degrees but only 30 minutes to drop that amount, you're on the hairy edge of having enough heat -- probably only good to 30-35. If, OTOH, it takes about 2.5 hours to drop that much then you're good to about zero.

    But make sure the house is up to temp first. It takes probably 48-72 hours for all the drywall, etc, to warm up once heat is turned on in a previously cold house.

    60K BTU (your net) should be sufficient for a 2500 sq ft house anywhere south of Minneapolis, if it's properly insulated.

    So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
  7. woodturner9 | Feb 06, 2007 12:37am | #7

    FWIW, 2 to 4 degrees F per hour is a "rule of thumb" for a properly sized furnace - so it sounds like it's working within spec.  The unit with the 119F register temperature may well be oversized and thus less efficient.

  8. doodabug | Feb 06, 2007 03:24am | #9

    Your post made me curious, so I did some checking today. I was working at a house today that had 80% furnace installed this past Friday.

    Outside temp today -10

    I put oven thermometer in register closest to furnace.

    TIME                          HOUSE TEMP            REGISTER TEMP

    7 am                             55                             87                      

                                       60                             90

                                       65                            100

    9:30 am                        70                            104

    2 1/2 hrs raise temp 55-70

    second cycle on furnace

    9:35 am                      66                               100

    9:58 am                      70                               104

    23 minutes to raise temp 66-70

    Don't know if this means anything to you, but that is what I found out.

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

FHB Summit 2025 — Design, Build, Business

Join some of the most experienced and recognized building professionals for two days of presentations, panel discussions, networking, and more.

Featured Video

How to Install Exterior Window Trim

Learn how to measure, cut, and build window casing made of cellular PVC, solid wood, poly-ash boards, or any common molding material. Plus, get tips for a clean and solid installation.

Related Stories

  • Affordable Scans, Accurate Plans
  • FHB Summit 2025 — Design, Build, Business
  • A Summer Retreat Preserved in the Catskill Mountains
  • Fine Homebuilding Issue #332 Online Highlights

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 70%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data