Mistakes on the R-values will have a compound effect on your heat loss/gain calculation results.
“OK, fair enough, describe the procedure please.”
“They have 2-foot thick stone walls with no insulation, old single-pane wood frame windows with handmade glass — you know, the wavy antique glass — wide plank flooring over a basement and wooden stairway to the attic.”
“R-values?” I asked.
“R11 walls, R2 windows and R19 attic floor.”
“Where did you come up with R11 for stone walls?”
“Someone told me that.”
“Same for the windows?”
“Yes and the homeowner told me the attic was R19.”
Did he bother to go up the stairway to confirm the insulation type, thickness and look for gaps where things like ceiling lights can often create gaping fissures where Btu freely escape? No! It doesn’t matter whose heat loss/gain program you use — garbage in equals garbage out. My friend ended up installing a second boiler to handle two of the five zones and had to eat the cost. When I asked why they don’t do their own heat loss/gain calculations, they responded they don’t have the time and/or they hate math.
The list of objections I get when asking fellow contractors to do their own heat loss/gain calculations are: It takes too long; wholesaler does it; assume the size needed based on past experiences; have always used 20 Btu/h per square foot for cooling and 40 Btu/h for heating; use numbers off old equipment for sizing; and “I thought the old lady would die before I had to fix anything.” (More on this later!)
The list of favorable comments from those who do their own heat loss/gain calculations are: The rock solid foundation on which I build the comfort systems my customers deserve; accepted by the AHJ and the court system; provides the knowledge of knowing my designs are spot-on; forensic analysis; establish trust and confidence, which means winning with higher bids; dial in outdoor reset curve; and determine proper size for boilers, furnaces, heat pumps, minisplits, ducts, piping, radiators, etc.
With today’s programs, it’s never been easier to run the calculations. Once you have measured rooms, windows, doors, ceiling height, and gathered information regarding insulation, you can fill in a default for each of the categories or click on the drop-down list while entering the type that best fits your application. Take that 2-foot thick stone wall the wholesaler’s inside guru had assigned as R11. In order to create a custom input, you first need to obtain the U-value, which the program will use to be the multiplier for net wall square footage (gross wall minus windows and doors). Online research reveals stone walls have an R-9 value per foot of thickness for a 1.8 R-value. Here are the formulas:
U-value = 1/R-value 1/1.8 = U-value of .56 and you can multiply that times the net wall square footage to determine the heat loss for the walls.
R-value = 1/U-value or 1/.56 = R1.8
Mistakes on the R-values will have a compound effect on your heat loss/gain calculation results. Back in the dark ages when we did not have computers and did this math by hand, it was tedious and did take a great deal of time when compared to utilizing a computer program.
“The old lady will die first.” That was one contractor’s response during a deposition and the old lady was far from dead. In fact, she opened her purse-strings and hired a high-priced law firm once she heard that remark. Oops. They hired several engineers to do a forensic study of her home and left no Btu untraced. I was hired to determine why the radiant heating in her master bedroom and bathroom couldn’t climb above 58° F during design-day conditions. Imagine being wheelchair-bound at 95, naked and wet in a 58° bathroom. She was madder than a wet hen!
Her son told me they offered to have the contractor hire whomever he needed to figure out what was wrong, have it fixed, and they would pay the cost. He said he understood everyone makes mistakes and they just wanted things fixed.
The sad part was that the contractor’s Elite Software RHVAC program, based on ACCA’s Manual-J program, was spot-on. What he had failed to do was take that heat loss information and use the WarmboardÒ chart to determine the actual Btu output per square foot and then compare the resulting output to the net required Btu for heating those two rooms in the master suite. Had he bothered to do that — and WarmboardÒ instructions clearly indicate that must be done — he would have known he was going to need supplemental heat. Flat panel radiant radiators, sized to accommodate the shortfall in Btu utilizing the low water temperature produced by the geothermal system were the perfect solution. Discomfort resolved!
Performing heat loss/gain calculations used to take up a day’s time way back when we did all the calculations by hand, but not any more. You can whip through computer-based design software programs in under an hour on a large residential home project.
My wholesaler does that for me. Good luck to you if they get it wrong. Who pays to go back and make things right? You do, and you were the responsible party anyway, as my good friend discovered.
I know what size is needed from past experience or I’ll just go by the energy ratings on the old equipment. Read on for how that can bite you in the arse.
Long ago, before homes were not insulated, the rule of thumb was 20/40-Btu/h per square foot for cooling/heating here in Southeast Pennsylvania. It’s a good way to get your thumbs broken today! I’ve seen situations that required less than 10-Btu/h per square foot in timber-framed homes using R40 SIP panels. If you don’t run the numbers, they might just run you outta town!
A few months ago, a homeowner called seeking help. Their two-year-old 3.5-ton heat pump was driving them to the poorhouse with $2,000 per month electric bills. In addition, they could not rise above 62° on colder days in their first floor wrap around addition. A wholesaler had been involved, after the fact, to see if they could help because they had sold the equipment and they utilized the Elite RHVAC software to run a heat loss/gain calculation. The homeowner provided me with a copy of the RHVAC results, but when I had the opportunity to study the room-by-room inputs, I realized they had failed to properly measure room dimensions as well as the windows, and there were a ton of windows — all single pane with wood frame. One room was listed with its three walls facing the same direction as if east and west no longer existed! 1.5-foot stone walls were given R11. I met with the young lad who had run the calculations and asked about the measurements.
“I took a best guess.” I asked if he had any formal training on the RHVAC program.
“No, I just opened the program and started running calculations for customers.” I encouraged the branch manager to get the lad some formal training.
The installing contractor called me after finding out I was looking at the job. I asked him if he did his own heat loss/gain calculations.
“No, I just put in what I know is right.”
On a subsequent call, he asked what I had determined. The wrap-around first floor addition, with its 1.5-foot thick stone uninsulated walls, required 2,799 cfm, but was only receiving 400 cfm from the single 14-inch flex duct. According to my duct size calculator, that 30% compromised flex duct was capable of supplying just 400 cfm. I call it my Wheel of Fortune because we use it to ensure our duct systems are properly sized to deliver the correct cfm, and deliver air quietly. We also use it religiously in forensic analysis for systems that do not work properly. No wonder they had burned through three blower motors in two years’ time! I suggested he could resolve the issues if he were to install mini-splits.
The owners wanted their comfort issues resolved, and tearing open ceilings and walls to revise ductwork was not in the cards. Given that the home actually needed more than a 7-ton heat pump, the reality was it simply could not be done. We installed several multi-head inverter mini-split systems and were met with numerous challenges due to the construction of an original stone home wrapped with a stone walled addition.
The new accurate Elite RHVAC heat loss/gain calculation not only revealed why the existing 3.5-ton heat pump system with its auxiliary 15-kW resistance heat (think electric toaster in a duct) package and undersized duct system were never going to be adequate. It gave us the knowledge to address each room and established homeowner confidence to have us install the multi-head inverter mini-split systems. We had no sooner completed the installation when a Polar Vortex, setting record low temperatures, descended upon our area and put our newly installed mini-splits systems to the test. In spite of ambient air temperatures well below the 10° design-day conditions we had input for our RHVAC program, the homeowners reported that not a single room fell below 68°. Although they don’t have enough monthly electric bills yet for a 12-mointh comparison, they did note that even with two extreme cold spells and the Polar Vortex, their bills are less than half of what they had been previously.
CYA (Cover Your Ass-sets) and do your own heat loss/gain calculations. You won’t regret the investment.