Does anyone have an inexpensive method to "clock" a combustion furnace to estimate BTU output similar to Natural gas, but for propane, kerosene, or oil? I work in the Weatherization Assistance Program and often the nameplates are missing from existing furnaces. Without BTU output it is tough to do an accurate computer model of the home. Thanks!

Views: 397

Reply to This

Replies to This Discussion

For natural gas, run only the furnace for a given time, mark the dial difference on the meter and multiply the gas used by the heat multiplier for your gas supplier. This will give you a ball park estimate.

For propane, you can look at the burner orfice size.  there are charts that give the btu rating for the orfice size. then multiply by the numbers of burners.  will give approx output.  LP orfices are usually slightly smaller btu than Nat. ones.

Follow the link

Thanks for all the comments plus the link. I think based on them I have enough information forfollks in the field to get close enough to the correct size furnaces for modeling the houses thanks all.


You mentioned oil, but the replies seem to all be for gas, unless I didn't read correctly.  For oil you can look for the nozzle size.  Sometimes it is notes on the service tag or in the manual, if still around.  In some cases you might be able to call the service company as they may have that noted for their HDD fuel calculations or service work. 


Thanks, I did find that out. In weatherization we deal with some really old furnaces, so sometimes getting a ballpark furnace size is the best we can do but the nozzle sizes for oil seem to be pretty specific.

For the oil burning furnaces, you should check the pump pressure. Older furnaces run at 100psi, and newer ones run at 140psi. When the pressure is higher, you need to cross reference the nozzle size to get proper Btu ratings. Plenty of reference materials are located on the Beckett website.

For propane figure about 20-25k per burner rated input. Varies some form unit to unit but 22k is typical.

Thanks Bob, we'll go woithout. It should be close enough without having to factor in pressures and temps, etc and  complicate the process too much.

I'll apologies in advance for drifting here a bit, but your "close enough" comment threw me back to my beginning in this business (05) when I questioned every number we use.  The idea of pinning down the performance of a home to the last tiny detail is laughable when we consider just how many of our inputs are "close enough" numbers.  From insulation values, HDD, window performance, and air leakage (to name a few), we guess and we guess and then carry our calculations out to two decimal places (or the computer does).  I think my tape measure is the only real source of accurate information :).

I enjoyed the comment



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

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
1 hour 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…"
2 hours ago
Diane Chojnowski posted videos
11 hours ago
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
13 hours ago
Profile IconMaren Cooke, Steven Antonini and First Choice Power joined Home Energy Pros
13 hours ago
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…"
15 hours ago
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
17 hours ago
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
18 hours ago

© 2015   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service