Replies

1. 
   b_coplin | Jun 30, 2023 02:57am | #1

   "Can you show me bin hour data--or any empirical evidence--to support your position?''
   I suspect your contractor has chosen the lowest temperature your area routinely sees--but this is only for an hour or two a year.

   If you are in a mountainous area, it's possible that your local conditions are different than the nearest weather station; I would still press for measurements.

2. 
   BirchwoodBill | Jun 30, 2023 07:14am | #2

   Run a report for temperature from the the manual and then one for the lowest temperature. Ask the contractor if that changes the equipment recommendation or the size of the ductwork.

3. Expert Member
   Michael Maines | Jun 30, 2023 10:17am | #3

   Considering that just a few months ago we had -20°F in CZ6 (Maine), I can see why they may want to be conservative. If you have a poorly insulated, drafty home, equipment may not be able to keep up. But one of many advantages of a well-insulated, airtight home is that it can more easily ride out those brief extra-cold spells.

1. 
   buildzilla | Jun 30, 2023 12:22pm | #4

   yeah, this would be for a new high performance build, so i'm thinking to stay the course.

   i told the people that i trust the ashrae data, and they were like ok,
   just don't come crying to us if your house is cold (i'm paraphrasing) :)

   i punched some diff design temps into cool-max and for this case, it was about 1000 btu for every 1 degree F (eg the diff between -10 and -20 was like 10k btu)...

1. Expert Member
   Michael Maines | Jun 30, 2023 12:36pm | #5

   Few HVAC contractors have much experience with high-performance homes, and their worst nightmare is a client calling to say they aren't warm enough.