New furnace vrs old furnace.

[92rslt1]

Ok so here my old furnace.

1968 International Furnace model HG 130a
Its ratings are
130 input btu
104 output btu
.20 static pressure
temp rise 70-100*

I guess its an 80 percent efficient, but based on its $200 monthly gas appetite, I doubt it. It constantly kicks on and off every 5 minutes. my house is split level so my basement family room is freezing and my up stairs is generally OK. The ducting has been modified from the original configuration and I'm guessing the static pressure is way too high. They added a small cold air return and blocked off a few ducts.(cold air return was just an opening on the side of the furnace before)

Anyways I'm in the market for a new furnace. I want a rheem model after reading several reviews and consumer reports I think that's the brand for me. I'm going to get a 90k btu 2 stage multi speed furnace. Rheem 95% Furnace Model # RGRL09EZAJS. I am still unsure on a t sat. So heres my questions

Should I have it set up so the Tstat controls the stages or the furnace board control it? Is it more energy efficient to have the tsat do it?

I'm on a big money saving spree switching all my windows and doors to HE. (even my bulbs to H.E.) My house is 2000k square feet. 1000up/1000 down. The windows, doors and attic will be fully modern by the time the furnace is installed. The walls of the house... I have no idea what is in them from 1968.

I'm going from a 103k btu to a 90k so I'm hoping my savings will be noticed instantly.

Thanks!!

[smooth_operator]

Your gas bill also depends what temp you set on your t-stat. If you set 75 and don't do set backs, it's not really bad for the unit that 43 years old in my area. Did you try to use energy savings calculator on Rheem website?

[seatonheating]

Unless an actual heat loss calc is performed who knows what kind of energy savings you will get.

What area are you located in? Heating degree days plays a large part into energy savings.

[amd]

I guess its an 80 percent efficient, but based on its $200 monthly gas appetite

If it has a standing pilot and draft hood, I doubt it's above 65%.

If the furnace is still working, consider focusing on reducing heat loss first; getting a professional energy audit and blower door test done is a good idea.

90k input may or may not be correct size.

[beenthere]

So you already decided that your house needs a 90,000 BTU furnace after you make all these improvements? Most 2,000 sq ft homes with all those improvements could use a much smaller furnace then a 90,000 BTU 95%er.

Your lower area won't be much better with an oversized 95% efficient furnace then it currently is with your oversized 80% furnace. A load calc should be done taking all your improvements into consideration. Might find you only need a 50 or 70,000 BTU 95%er.

[REP]

Well let me try what you seem to be doing.
I say go with a 60,000 furnace.
Where did I get that from,,,,i pulled it outta thin air.
Was a real load calc( a manuel "J") done,,,no,isn't that just a salesman's trick anyway?
How will the ducts work with a new furnace,,,who cares you already spent money on that and a manuel "D" is smoke and mirrors right.
The way you figure it installing a new furnace is more important that your comfort for the next 20 years,but it could mean that you will be paying ever climbing fuel prices with the wrong size furnace and ineffiecient ductwork.
But hey at least it will be new.

[George2]

If you oversize a 2-stage furnace it will almost never need to go to the high stage.

You've just wasted your money and you won't get the comfort your seeking.

Do the insulation/windows/chaulking improvements, then get someone that does a Manual J and will size the furnace correctly.

I've seen 60,000-70,000 btu furnaces work in a home your size without the timprovements you're talking about.

[92rslt1]

Thanks for the replies and warm welcome! Tough crowd here. I live in upstate ny. The M J test showed I needed 77k btu. I wanted to go slightly bigger based off the fact that my house is a 1968 national home brand house and is likely to have very little or not have any insulation in the walls at all. They seem to think a 77k would be fine.. It might be and I might find that with my new windows and doors its going to be. However, If it turns out its not, them Im out thousands of dollars and my house is cold still. Prior to buying Im going to have a full energy audit done to be the determining factor.

My stat is set at 68 and is on a timer and reduces to 62 when im not home and its at 66 on night and on weekends.


If it has a standing pilot and draft hood, I doubt it's above 65%.


I originaly thought it was 65% too based on research I did saying that most installed in late 60s are 65% however the input of 130 and output of 103 = 79% efficentcy unless Im leaving something out.

I was curious what t stat is recomended most for a 2 stage furnace?
Should I have it set up so the Tstat controls the stages or the furnace board control it?
Is it more energy efficient to have the tsat do it?

[Hunter844]

Count me in the camp that says if you are already planning to do several home upgrades, do those things first...UNLESS your guy that did a manual j also did a "what if" scenario showing what you would need factoring these future upgrades into it.

About the thermostat, just make sure it's at least capable of providing 2-stage heat you'll be fine. That in most cases would require a new control wire run to the thermostat location. You would have to have a "communicating" furnace and control system installed to use less wires.

[amd]

I originaly thought it was 65% too based on research I did saying that most installed in late 60s are 65% however the input of 130 and output of 103 = 79% efficentcy unless Im leaving something out.



It's around 80% when running continuously.

There's a draft hood continuously venting heated air, a pilot continuously burning gas, and a thick heat exchanger which could take several minutes to warm up at the beginning at each cycle.

65% max - probably lower.

If the furnace is grossly oversized (short cycles), it could be averaging only 50%.

[seatonheating]

It's around 80% when running continuously.

There's a draft hood continuously venting heated air, a pilot continuously burning gas, and a thick heat exchanger which could take several minutes to warm up at the beginning at each cycle.

65% max - probably lower.

If the furnace is grossly oversized (short cycles), it could be averaging only 50%.

Great post amd!!!

I think a lot of the time we forget to take all operating factors into account and only rate furnaces on their steady-state operation. This should be a sticky.

[BaldLoonie]

Definitely get a 2 stage stat so staging is based on house needs. That way you can stay on low as much as possible.

The 09 will want to move 1400-1500 CFM on high. That is a lot of air for a 2000 sq ft house. Hopefully the dealer looked at your duct system to be sure it can handle that much. The old furnace probably moved considerably less air since it ran a very high temp rise. If the duct system is undersized, it could sound like a wind tunnel in the house on high fire.

[92rslt1]

Definitely get a 2 stage stat so staging is based on house needs. That way you can stay on low as much as possible.

The 09 will want to move 1400-1500 CFM on high. That is a lot of air for a 2000 sq ft house. Hopefully the dealer looked at your duct system to be sure it can handle that much. The old furnace probably moved considerably less air since it ran a very high temp rise. If the duct system is undersized, it could sound like a wind tunnel in the house on high fire.

Thanks for the advise. I think new ducting might be needed too. Im positive the return on this one is way too small. It currently produces a heck of a whistling noise so I cant imagine what a high speed blower would do.

when the tag on the side says .20 static pressure is that a max rating or optimum?