New system air and heating

[billyb]

Hello everyone.........I need some info on an airconditioner,or heat pump and gas furnace, old air is 3.5 tons dont know furnace output, have a couple proposals already one left me a manual j 8th edition report which says for heating summary equipment load 63012 btuh and latent cooling equipment load sizing total load 33695 req. total capacity at 0.70 SHR 3.3 tons.

My old system installed in 1989, house is 2100 sq ft, 2 story got proposals on airconditions and heat pump in the 13 seer,14 seer and 15 seer with a 3.5 tons also furnace 92.1 afue mcb 93000btu, 93.1% afue mtb 94,000 btu and 95% ics 93000btu all are for Carrier system so far

My question is that I want good systems without over doing them , not larger than needed,wont be making a decision until late march.

I live in southern Illinois

Thanks

[hvac-learning]

we use RHVAC for manual "J" load caluation and it does a good job but some area need more heat or a/c btus do to infiltration in your area. Get a list of referances go check them out call , stop by, are they listed w/ the BBB. have the had any problems weigh the pro`s and con and you will be off when spending your with a company that you`vd checked out and has your confindence.

[beenthere]

I wouldn't put more then a 80,000 BTU input 90% in.

[mgould2]

I think you would be with a smaller a/c and furnace. Some thing like 3 ton A/C with no larger than 80k btu. A multistage system will provide better co

[sktn77a]

You could go with the larger units if they are multistage.

[beenthere]

Nothing wrong with using a 3.5 ton when the calc says 3.3 ton load.

Using a larger 2 stage furnace, just means he loses some of the comfort he pays for. Since he won't get the long run times at milder out door temps.

[merlin73]

I would also go with the 80k furnace with 2 stage and vari speed blower, and i would go with the 3.5 ton with 2 stage compressor.
You will get the longer run times and comfort levels you are looking for.

[sktn77a]

By "larger", I meant 90,000BTU/3.5ton.

[beenthere]

I would also go with the 80k furnace with 2 stage and vari speed blower, and i would go with the 3.5 ton with 2 stage compressor.
You will get the longer run times and comfort levels you are looking for.

Trane makes a 2.5 ton 2 stage.
Don't know of anybody else that makes a 2 stage of any other size in half ton sizes.

[beenthere]

By "larger", I meant 90,000BTU/3.5ton.

First stage is usually 65% of high fire/
so 65% of 90,000 is 58,500, not much less then his design load BTUs.

An 80,000 would getr him below 50,000, so he could have longer run times, and still have capacity to spare.

See the post by key1cc, about his over sized 2 stage furnace.

[tedkidd]

That seems really big for 2000 sf! What infiltration did they figure?

Are you air sealing and insulating so you can get smaller equipment? Did they do a blower door test (I do for all new heating equipment recommendations - then I show the benefit of an extra day's labor tightening the house up)?

I'd think 60-80mbtu multi-stage and 2-2.5 ton should be plenty at 6000 degree days. If you are a "user" of air conditioning (v/s 5 days a summer) stretch for multi-stage.

[billyb]

Thanks for everyones info new system, I will be getting a blower door test from my utility company just have to call them and set it up so I can insulate and chaulk house; to cut down on some air pockets house is 20 years old , that way I can buy the correct aircondition and furnance. Dont want to overkill or underkill the systems.

thanks

[sktn77a]

First stage is usually 65% of high fire/
so 65% of 90,000 is 58,500, not much less then his design load BTUs.

An 80,000 would getr him below 50,000, so he could have longer run times, and still have capacity to spare.

See the post by key1cc, about his over sized 2 stage furnace.

Thanks Beenthere - I think we're in violent agreement actually. Yes, I read Key1cc's thread back when it was active. Heat loads are calculated at a reference outside temperature, if the temperature falls below this reference, heat loss will be greater. While oversizing 2 stage equipment because installers are unable/unwilling to do a proper sizing calculation is bad, if the reference temperature heat loss lies between the two stages, that would appear to represent an ideal compromise between low stage comfort and high stage "reserve". Whether that's an 80,000BTU furnace or a 90,000 BTU furnace depends on the accuracy of the load calculation and the availability of sizes for any given manufacturer.

[tedkidd]

Thanks Beenthere - I think we're in violent agreement actually. Yes, I read Key1cc's thread back when it was active. Heat loads are calculated at a reference outside temperature, if the temperature falls below this reference, heat loss will be greater. While oversizing 2 stage equipment because installers are unable/unwilling to do a proper sizing calculation is bad, if the reference temperature heat loss lies between the two stages, that would appear to represent an ideal compromise between low stage comfort and high stage "reserve". Whether that's an 80,000BTU furnace or a 90,000 BTU furnace depends on the accuracy of the load calculation and the availability of sizes for any given manufacturer.

First, those heat loss calcs have fudge factor built in - so don't add fudge to fudge.

Second, unless your home has no thermal mass and tons of air leakage you don't even have to worry about design temp - it happens for such short periods. (*** Make sure you don't go for crazy setbacks when it gets really cold - your home may not move UP from 50, but it'll likely stay at 70)

If it goes 20 degrees below design temp it'll take a LONG time for your furnace to NOT KEEP UP. In other words, the heat already built up in your house will be lost slowly over that period and MAYBE your 70 degree house will drop to 65 - after a few days. In that once in 50 years situation, if you want to keep 70 degrees - buy a couple space heaters.

You want as low a second stage as possible - that's why high end furnaces now have a 3rd stage. MOST OF THE TIME 3rd stage is oversized! You want to get as close to properly sized for "most of the time" on your low stage.

Don't spend more on equipment and more on energy for the next 20 years for a once in 50 year event that lasts a few days! Put a sweater on for heaven's sake! Get a blower door test to know your infiltration. Fix it if it's bad.

[sktn77a]

Put a sweater on for heaven's sake!

Ha! Tell my wife that!



Keith

[beenthere]

Whether that's an 80,000BTU furnace or a 90,000 BTU furnace depends on the accuracy of the load calculation and the availability of sizes for any given manufacturer.

In this case.
Carrier does have the smaller furnace that already exceeds the load calc on high fire, with out going up to the larger furnace.

[billyb]

This message is to thank you guys for all your information very much appreciated............SKTN77a,b
eenthere,Merlin73,Tedkidd and all others

[billyb]

This is pictures of my install March 18,2009..........thanks guys.....sorry it took me so long to reply

[billyb]

This is the outdoor unit..................Thanks

[billyb]

Sorry forgot to attach pictures............thanks