Hello,

I frequently find that Manual J reports provided by HVAC companies are much higher than what Ekotrope estimates in the Energy Design Loads Side Bar. I've found window areas to be way off and not the correct U or SHGC. I've seen occupants 20+ to inflate cooling load. What I'm getting at is how close should the manual J and a modeling software's calcs be? Are we as raters missing something or is the HVAC industry trying to avoid the callback for when the system doesn't keep up beyond design temperatures? At the end of the day it's the HVAC contractor who is installing and standing behind the system, but seems like something that could be improved in the industry.

Thank you,

Dan Jarmolowicz 

i would love to hear the opinions of some of the other long time more Sr, raters - what is your take on sizing in general...

thanks Jay,

great insight and totally on point. I think we should all be excited to see commissioning coming in under our scope, i am not looking forward to the extra work, but it does allow for a path to mandate corrective action. it will be important to get a standardized testing protocol out to the rater community ASAP so we are consistent across the region. A great webinar for Rich to work on putting together for later this year.

i also would like to remind everyone, we are verifiers when it comes to sizing, the manual J should be coming from a trusted and certified source (eg. mechanical engineer). it is typically obvious when it is not and an easy flag to the municipal inspection dept when it needs to be redone. 

No doubt, there are some inconsistencies in this industry, and Yes the average HAVC designer is oversizing to 35 degree delta to avoid a call back on the few days a year we actually need AC in the Northeast... the issue in the calculations comes down to sensible load and Wrightsofts inability to properly calculate ASHPs  I suspect CoolCalc ect. all have the same issue. With a huge push by some states and utilities for go All Electric, the Cold Climate ASHPs are just going in at a rule of thumb: 1 ton per every 1100 sqft CFA. not optimal but a little better than the inaccurate sizing of the softwares. Truly unfortunate, luckily for us we have a fall back reference in the HERS softwares. Keep on reviewing those builder manual J's, just getting one is a win. The real education needs to start with the architect and these sizing loads done well before the building is framed. As a Rater, start that conversation as early as possible... 

In your case you knew the actual usage, in a new home that is fluid as we do not now the owners habits or what their comfort levels are.