Help! Gas furnace size proposals are all different
I would greatly appreciate any feedback on what would seem to be the correct furnace size. I have received 3 different bids for Trane XV95 95% efficient 2 stage variable fan furnace. All three contractors proposed different size BTU units including 60, 80 and 100btu. One said he did a load calc, to which I saw him measuring the house but I didn't see him measuring any windows. The other two contractors took a good look around, but did see any measurments. All see they are confident in the btu selection. All have are recommended from the Trane website and have great Angieslist ratings. I am obviously try to figure out who know there stuff best.
Here's my stats:
Portland Oregon area (temperatures can get in the twenties and maybe teens a couple days at year)
3 story house, including 880sf daylight basement with crawl space not slab
House built in 1993 with original Carrier furnace
Double pane windows
2x6 framing (I don't insulation ratings)
Trane XB13 3.5 Ton AC installed in 2007. Has hard time cooling the top floor below 75 degrees on 92+ degree days.
Daylight basement of ~900sf runs about 8 degrees cooler than rest of house. I do have a Rannai direct vent gas wall heater in the basement which can heat it quickly, but I would prefer to heat the basement with the main furnace, or at a minimum close reduce the 8 degree gap with the main furnace, and supplement with the Rannai if necessary.
Which one seems most correct for my stats. Thanks!
3 guesses huh or maybe the one really did a calc though hard to do without knowing window sizes. Usually the guessers are proposing the biggest equipment to be safe. Usually one wouldn't propose a small unit without knowing for sure it is sufficient.
Call Sky Heating, he posts on here by that username. Travis will take care of you.
I have been out to the house, I am the one proposing the 60K BTU, i will be going out on Saturday to do a full manual J to prove that the 60K is the right size since I was in a rush when i went to the house Wednesday morning. We have offered to replace the furnace with an 80k if it can not heat the house but for our mild climate and 24 degree design temp it takes a 5,000 sq foot or larger home before we run into needing larger furnaces.
Originally Posted by BaldLoonie
We have looked into the temperature stratification and I am proposing to install a damper to the upstairs to help push more air downstairs and adding another manual damper on the lower floor ducts to adjust to push more air upstairs in cooling. Zone system is not a very feasible option for this home.
Go with the smallest furnace and make sure he'll be in business in case he needs to come out and replace it for free. Make sure that he understands the temperatures you expect and he'll guarantee that in writing. Does the 60,000 come with a 4 ton blower (needed for your 3.5 ton A/C)?
Any particular unique issues to be aware having a daylight basement that is 8 degrees cooler than the rest of the house? How to best solve?
Good for you. The answer is; give it the guy with the Manual 'J' in hand. I had to put add a zone for our walk-out basement. Fortunately, the plenum was already split for the purpose of "balancing". With the heat load a full third of the main floor, there is no balancing in winter and the lower is going to be cool in summer since the staircase is open.
Don't be afraid to give people the options. Many have the money and the desire to have it right.
Update, after performing a full manual J using Adteks Accuload version 8 ACCA approved we came out to a heat loss of 37K BTU's at a 20 degree outside temp and 71 degree indoor temp with worst case scenario insulation values on an average sealed home.
Now the OP can feel comfortable with the smallest furnace. Literally Sad that someone would propose the big furnaces but we see it constantly around here too.