How do I Know if my Load is Correct!?

The goal of conducting a load calc is finding the CORRECT load on a house. How does one know if the final answer that Wrightsoft provides is correct or not? The short answer is they don't - unless the check their work thoroughly and verify that pertinent project project information has been correctly specified in the model.

Wrightsoft software doesn't know if a user has calculated ceiling, wall, or floor area incorrectly. The program doesn't provide an error message if a user entered 24,000 btuh (2 tons!) for appliance loads as opposed to a more realistic 2,400 btu (2 tenths of a ton!). The best way to figure out if a load is correct is to DOUBLE CHECK all areas, R-values, U-values, HTM's, and final loads.

Below is the checkout process that I use on every load.... Feel free to add to it!

▪Is exact location of home known? Does it match specified climate data?

▪Is orientation known? Has it been verified with homeowner / builder? Does it match orientation as specified in Wrightsoft?

▪Are level elevations and ceiling heights correct?

▪Have all rooms drawn on plans been drawn in Wrightsoft? Is every room set to “include in load” (this can be changed on the properties sheet for each room).

▪Have all windows been drawn in Wrightsoft? (Be careful, glitches in the Wrightsoft program sometimes cause windows to disappear).

▪Are wall areas correct for rooms with multiple ceiling heights? Is roof area correct? Is floor area / perimeter correct? (remember, slab on grade construction is evaluated by the linear length of the perimeter).

▪Have floor, wall, and ceiling r-values been verified in the component construction report? Do Heating and Cooling HTM’s make sense?

▪Has duct location, insulation, and infiltration been specified for each room?

▪Are U and SHGC values correct? Have these been verified on site, with builder, or with window rep?

▪Have window overhangs been specified?

▪Is glazing in the ballpark of 50% of the total cooling load?

▪Have occupant loads been included?

▪Have appliance loads been specified for kitchen, utility, office equipment, etc…?

▪Have infiltration and fireplace details been specified?

▪Has fresh air ventilation been specified? ERV, HRV, supply only?

▪Are warning messages displayed in the load meter?

▪Is the square foot per ton ratio somewhere between 800 and 1400 (for a new home)? Does this make sense for the house?

Tags: calculation, j, load, manual, manual j, training, wrightsoft

Replies to This Discussion

Permalink Reply by dale conner on March 5, 2011 at 10:50am

I found the drawing feature to be very frustrating to master so I mostly use the worksheet feature. I'm assuming the glitche is in the drawing board feature, is that correct?

Permalink Reply by Kyle Brown on March 9, 2011 at 6:08pm

Dale, yes, there are several drawing board related glitches that are basically all related to one setting: grid point snap spacing.

Basically, the smaller the snap setting number is, the more likely glitches are. Problems can range from windows disappearing and rooms resizing themselves to the load changing drastically with just the click of a mouse (while not changing anything in the drawing).

Folks get tempted to set the snap points to increments of 3 inches or lower especially when drawing homes with walls on 45 degree angles. However, If you leave the grid set to 12" increments and set the snap to 6" you will still be able to draw a very accurate footprint and should be glitch free!

Permalink Reply by Chris Laumer-Giddens on April 20, 2012 at 8:15pm

I've had my grid and snap set to 4" for a couple of years now, and the "glitches" rarely occur, if at all.
I'll occasionally set snap to 1" to accurately line up my backgrounds to the grid, then immediately go back to 4".
This was a the recommendation from my good buddy, Hamilton, with WS technical support.

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