Thanks, Ryan. I did get a total of 4 quotes and 3 were for 3 ton Bryant 80% gas furnace. Two of the three bids proprosed 66,000 BTU input and 54,000 output while the third one purposed 110,000 input/89,000 output. Wouldn't the two bids for 66,000 BTU be too low on the BTU's since my 1978 furnace has 80,000 BTU input?
I asked for a heat loss calculation for the 110,000 BTU bid and he does not do a Manual J. He based his bid upon my square footage, windows, number of vents, and the old furnace capacity. He's been in business awhile with a good reputation for his installation work. I also have a very standard 1978 split level with original single pane windows and insulation so it isn't a complicated house. It seems to me that 66,000 BTU on the first two bids is too low and the 110,000 BTU's on the third bid is too high. Is there something I don't understand with this?
None of the 4 bidders included a copy of a heat loss calculation. All were from well-established companies so I wonder how difficult it is to have this done? I wonder how much I need to understand about these details? My neighbors look at me like I'm speaking another language when I ask what their BTU input and output is on their furnaces.

btuexpress

you need a load calculation. Since you live in PNW which has mild/moderate winters, I would think a 50 KBTU furnace would be more than adequate. I suggest Am Std Freedom 80 Comfort R two stg furnace(with var spd blower) or Am Std Freedom 80 two stg(without var speed blower).

and you can perform the man J yourself for a small fee. well worth it.

here is the link.

www.hvaccalc.com

also see link for AmStd Furnaces

IMO

Here is a link that might be useful: American Standard Furnaces

Did your 80,000 btu furnace keep your house warm? If so there is no need to go higher. Now based on your experience you can try to figure out how oversized your unit was (if any). If your furnace ran continuously on the coldest day of the year to maintain your thermostat setting than it is perfectly sized.
You want long run cycles so the heating is more even and it is more efficient. How long did your furnace run on the coldest days? Maybe it ran for 10 minutes and then shut off?
80,000 btu and 3 ton cooling is a very common size. I am not familar with Bryant units but I would be surprised if they don't make a 80,000 btu unit that would work for you. Did he give you a model no.?

You have to consider the efficiency that your unit was working at. Your 80k furnace may have been 70% efficient with a net ouput of 56k BTU's. The person quoting a 110k furnace seems to be oversizing it by a lot. I agree on the heat loss calculation as being necessary if they want to prove that you need to change size.

Thanks Tigerdunes, funnycide, and Ryan. Answers to your questions:
1. The Bryant model # proposed by the contractor suggesting the 110 BTU input is 310AAV036110 single stage (80% furnace - 1 stage). His 2-stage suggestion is 312AAV036110.
2. Two others bid Bryant model 312AAV036070 -- this onehas 66K BTU/54K BTU if I'm reading the spec sheet correctly (could be 70K input?). It appears in the specifications of the Bryant manual that there isn't a 3-ton furnace at 80% between the 66K BTU input and the 110BTU input.
3. My 30 year old Rheem furnace has kept the house warm, although kids have grown so I shut off 1 - 2 extra rooms plus the small family room downstairs and those rooms are a bit colder. I guess I haven't paid attention to running time of the furnace (maybe 10 minutes makes sense on the cold days but I am really not sure.) A friend says if I get the 110,000 input single stage the theromostat will turn the furnace off when the house is at set temp. What would be the downside to installing the 100K input furnace? I planned to get a programmable thermostat.
The main reason the contractor suggests 110K input is that I have single pane windows. Now I wonder if I should be installing vinyl windows before installing a new furnace?
I think I'll have to ask for more bids as I don't want to undersize or oversize the furnace. It sounds like I can't avoid the heat load loss calculation. My house is in a neighborhood of like models so thought I could go with a "typical" furnace. Thanks for all your advice and I'd appreciate further comments. This process has turned out to be more complex than I initially thought it'd be.

It can be a complex process when everyone is telling you different sizes. Oversized furnaces aren't efficient and tend to have a shorter lifespan. Ask on the phone when you're looking for estimates for a heat loss calculation. Good luck. I would ask the 110k btu guy why he's oversizing when the old furnace did just fine and an oversized furnace wouldn't be good.

Thanks, Ryan. I did a heat loss calculation through my gas company today (65,000 BTU heat loss). (The man I talked with ran numbers for various aspects of my house in a computer program he had so I think the heat-loss calc is in the ballpark of accurate. He knew a lot and talked with me for a long time.) The range of furnace I need is in the range of 70,000 -80,000 BTU for input and 56,000 - 64,000 BTU output based on the heat-loss calculation. At this point I agree that the 110K input is too high. The Bryant model that is closest to my BTU needs has 66,000 BTU in and 54,000 BTU out. Those numbers are slightly below my BTU range so I'm now not sure if that undersizes the furnace?? Does anyone know if being under the range by 4,000 BTU's will matter? I might need to go to a different brand as I believe Trane has a model with 80,000 BTU input and 64,000 BTU output. My 1978 gas furnace has 80K input but I've been told at 70% efficiency it performs closer to 56,000 BTU output. Again, thanks for all help. I'm getting an education here. I plan to get a few more bids to see if it adds any clarity. The 110,000 bid contractor basically says he knows what he is doing so I've been reluctant to ask him his rationale. The low fire range of his 2-stage furnace bid fits my BTU range with 72,000 BTU in and 59,000 BTU out but then I probably wouldn't need the high fire range of 110,000 BTU in and 89,000 BTU out so not sure if it's worth getting a 2-stage.

The heat loss figure is based on the outdoor design temperature (if a true Manual J was done), so at the design temperature (which might be 10*, 20*, etc.) the furnace should be running constantly. The link below has the sizes that the 312AAV comes in. Have you considered a 90% efficient furnace? You did mention that you are most likely moving in 5 years, and I'm not sure how much this would attract the seller, so this may be the reason you're not considering them. A couple more bids sounds like a good idea...

Here is a link that might be useful: Bryant 312AAV capacities

Thanks again, Ryan. The link to Bryant capacities is handy. I did have a printout from the manufacturer. I think a 70,000 to 80,000 btu input would be right for my home. The capacity sheet shows a Bryant model with 88 btu input but it is a 4 ton unit and I need a 3 ton. So, with Bryant I appear to have a choice between either the 66,000 btu input or jump up to the 110,000 btu unit (in the 80% models). I now believe that 110,000 btu is too much.
I hesitated about getting a 90% efficiency furnace due to cost, having to redo venting, and the possibility that I will move in 3-5 years. Nearly everyone in my neighborhood has purchased the 80% efficiency so I hesitate to upgrade too much. Anyway, I appreciate all the advice. There's a lot more to evaluating the choices than I initially realized!

btuexpress,

I would think the 66K two stg 80% would be your "best size".

312AAV036070
80.0 efficient
66,000 input high stg
43,500 input low stg
54,000 output high stg
36,000 output low stg

however, I would upgrade to the var speed blower model-Evolution Plus 80V-Mdl 315AAV. basically same furnace as above but with var speed blower.

IMO

see attached link

Here is a link that might be useful: Evolution Plus 80V

If you want to stay with the Bryant dealer you can use the model #310AAV042090
80%
88,000 in
71,000 out
single stage

It's listed as a 3.5 ton but the airflow is the same as the 3 ton model. The size is the same too.
If you want to stay basic that would be a good choice.

Here is a link that might be useful: bryant

By all means, as stated by many, have (or do it yourself) a load calc done.

Incidentally, today on another forum, I read that closing off some rooms saves relatively little.

You could adjust your ductwork dampers (if you have them) for the best, most even, heating and cooling.

V

Why are you selecting an only 80% efficient unit?

The original poster explained that a few posts back.

Thanks all -- Here's a long message--basically asking about the best placement for the air filter and thermostat selection--sorry for the length! Didn't know quite how to shorten this one up.
I am considering the 66,000 btu in/54,000 btu out Bryant model in either one or two stage (thanks for the info, Tigerdunes). Funnycide--I also am considering the 310AAV042090 model since it is closer to the btu range I want: 88,000 btu in and 71,000 btu out. However, the 3.5 ton probably is too big?? Talked to a Bryant rep. today and he said it could work but might be more noisy. The American Standard Comfort R 80 series matches the btu range I'd like...just not sure I want to go with that brand (more expensive, etc.).
Does anyone know if it matters whether the filter is housed on the side or under the furnace? The contractor who bid today is the first one to tell me that the furnace will run more efficiently if the filter box placed under the furnace and then mounted onto a 18" metal box with a 16" opening on the side where the air intake is located (wall opening with a vented cover at base of the lower stairwell). My old furnace has the air intake on the side and the furnace sits on the floor (cement slab). The only air return is at the basement level of my split level house. There's a vent cover on the wallboard and I've been taking off the vent cover to change the filter. The actual side opening to the furnace is set back from this wall opening (across the wall studs) so I've reached across the wall opening to put a filter onto the furnace opening using electrical tape to hold it in place(!). The furnace itself is accessible via the laundryroom. It's housed behind louvered doors. The filter was supposed to be changed by taking off the front furnace cover but the side holder never worked well. The contractor bidding today said it's better to have the air enter beneath the furnace and go up through the filter rather than enter directly into the side of the furnace. He'd build the 18" metal box to get the filter box and furnace raised off of the cement slab and allow the air to enter the side of this box and then go up thru the filter to furnace. He's the first one to tell me about this information. Any feedback?
2. Any opinions on getting a Bryant programmable thermostat vs. a Honeywell 7 day touchscreen VisionPro 8000 thermostat?
I am hoping to decide soon before analysis paralysis sets in... seems to be a lot of choices with this purchase. If I knew I was going to stay in this house a long time then I'd choose the more efficiency options (90%, heat pump, etc)but my future commitment to living here is undecided. Thanks for all the input.

i looked at the difference between the 036110 and the 042090 and they are nearly identical except for the btu rating. They both have a 1/3 hp motor and the same blower wheel. The cfm's are nearly identical. Don't worry about being too big or too noisy. If it was blowing a little too much you can just switch to a lower speed tap.
As far as a bottom or side return, as long as the installation manual says you can use the side return you will be fine. Sometimes with bigger units (usually 5 tons) they will tell you that the bottom should be used. Some models use an external filter rack that is install between the unit and the ductwork. Other models have the filter inside the unit. Doesn't really matter.

Funnycide -- Thanks for the details about the 042090 model and the filter info. Two bids suggested raising the new furnace on a metal box with the filter box attached right under the furnace to allow intake air to upflow. At this point that seems fine to do. If I go with Bryant then I'll need to decide between the 66,000 btu input 3 ton or go for the 3.5 ton 88,000 btu input (042090). Trane does have an 80,000 btu input furnace so that one is also in the mix of possibilities. I'm on the fence whether I'd notice the 2-stage "comfort" sales features or if a 1-stage with a programmable thermostat would work just as well. If I can't wade through the details to a decision then it might take a coin toss. Thanks again for the info.