Sizing A Room Up - HVAC - DIY Chatroom Home Improvement Forum


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

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

Reply
 
Thread Tools Display Modes
Old 12-09-2009, 02:25 PM   #1
Member
 
Join Date: Dec 2009
Posts: 100
Rewards Points: 75
Default

Sizing a room up


As far as figuring up btu's per room, how do I do that. example: 10' X 12' X 10' Ceiling. I Know that would equal my cubic feet, but how do I know what btu's are needed, is there a rule of thumb for this?

Advertisement

Livewire78 is offline   Reply With Quote
Old 12-09-2009, 03:39 PM   #2
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

Sizing a room up


Quote:
Originally Posted by Livewire78 View Post
As far as figuring up btu's per room, how do I do that. example: 10' X 12' X 10' Ceiling. I Know that would equal my cubic feet, but how do I know what btu's are needed, is there a rule of thumb for this?
For room heaters it's 10w [34 BTUs/hr] per sq. ft., so it's 4100 BTU/hr plus or minus a wide margin, for your room.
For more precision there's always Manual J, for whole houses.

Advertisement


Last edited by Yoyizit; 12-09-2009 at 03:44 PM.
Yoyizit is offline   Reply With Quote
Old 12-09-2009, 05:04 PM   #3
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 4,300
Rewards Points: 2,178
Default

Sizing a room up


If you want to make an accurate analysis, you need to calculated the heat loss through the six sides of your room, and size your heater to produce at least that amount of heat. To compute heat loss through a wall, you need to know the temperature difference between inside and outside, and the R value of the wall. For example.

You have a wall which is 8 feet high and 12 feet long, for an area of 96 square feet. The wall is insulated to R-19. You plan to heat the inside of the house to 68 degrees F. The design outside temperature is 10 degrees F. Therefore the temperature delta is 58 degrees F. The loss through the wall is the reciprocal of the R value, or 1/19 BTU per degree per square foot per hour. So in this case, you lose 58/19 = approximately 3 BTU per square foot per hour, or about 300 BTU per hour total through the wall.

You make the same computation for each of the six sides of the room (include ceiling and floor), but note that the temperature difference between the room and the attic is not the same as the temperature difference between the room and the outside. Similarly, each wall has different insulation.

Do this for each room, add up the total, and you will know how much heat loss to expect under design conditions, so you can size your heater appropriately. Make sure you account for windows, they typically have lower R value than the walls they set in. Also, you need to adjust for air gaps, most houses are not very tight.

So after all this analysis, you may simply want to ask a furnace supplier, they probably know more or less what works in your area.
Daniel Holzman is offline   Reply With Quote
Reply


Thread Tools
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
Vents from boiler room RammsteinNicCage HVAC 3 03-11-2009 08:28 PM
Cold Room mikelbeck HVAC 14 01-16-2009 09:21 PM
Heat pump in non insulated nor heated room robdville HVAC 3 01-21-2008 03:51 PM




Top of Page | View New Posts