yes, I am experiencing the same thing here in the west coast of canada...basically same climate as seattle, inspectors wanting heat loss/load calculations...not that they know if they are right or not. But to get down to the accurate numbers takes getting so much info from the general contractor in regards to the materials used in the construction of the building that a day can be spent on just gathering info..adding cost to the quote that the puts your bid over the competition. If it was a blanket policy throughout each district/province/ state then we would all be on the same page for costs...until then...get the quote out based on past experience and carbon copy the heat load calculations unfortunately.
I think the fair way to do a design/load estimate would be for the responsibility to fall on the Architect/engineer, house designer. They have the responsibility for the integrity of the building and have been putting the responsibility on the trade for too long.
It's done in commercial buildings, at least larger ones and as long as building performance is an issue I think the design should be where it belongs, with the designer.
I'd bet one thing that would disappear if design/performance were an issue would be flex duct snaked all over an attic.
My rule of thumb in sizing is use manual j and then pick the smallest system that will fit the bill! I tend to (slightly) undersize as it adds comfort, reliability, economy of operation and lastly, customer satisfaction. I think we ALL tend to add just a little to make sure we are covered. This, i believe, includes the #'s you get from man J.
Have installed 50k BTU furnaces in 1800 foot split entries (900' per floor) in Montana and had nothing but praise for how even the temperature was throughout the home in the coldest weather.
Keep in mind that Man J does not include internal gain in heating calcs.
Can this question even be answered?
Isn't this like asking.. the person weighs 150 lbs
how many Calories does he need to eat every day to maintain his weight?
There are so many variables that you can't possibly give one simple answer.
Its a shared responsibly.
what program or method do you guys use for load calculations? Are commercial calcs easy once manual j is learned
Mike, actually, Manual J is for residential only. For commercial, there are (2) accepted methods, ASHRAE RTD and ASHRAE CLTD. These methods factor in required ACH and required ventilation applicable to the commercial and institutional market.
ACCA manual N is for commercial.
True. I forgot about Manual N. I use WrightSoft's RightSuite Universal. We also have HVACalc. It is a much simpler residential/light commercial heat loss/gain program. We only use it for little projects that don't need all the bells and whistles that we get from RightSuite.
What do you guys use for a wall R factor in old houses when the HO has no idea what insulation is in the walls?