Question: Three Stage Vs Modulating

[cvcman]

beenthere, at your cals then in cold weather if mine runs every 1/2 hr for 15 mins then in a full day it will run 12 hrs, then it would use 4 therms a day right ?

Thats still alot but not as many as im calculating. I clocked the dial on the meter that moves the fastest, on hi fire it took 25 secs to go around one time, low fire about 47 secs.

There has to be a way to see for sure unless I zero my filter minder on the stat, take an exact reading then let it run for a few day like this then see.

At any rate IF Jm is right it doesnt matter,he said I would have the highest gas bill on the block and use 40% more gas with a 2 stage firing at low whih again is where mine seems to run...

Thank you for trying to help me

[hvaclover]

beenthere, at your cals then in cold weather if mine runs every 1/2 hr for 15 mins then in a full day it will run 12 hrs, then it would use 4 therms a day right ?

Thats still alot but not as many as im calculating. I clocked the dial on the meter that moves the fastest, on hi fire it took 25 secs to go around one time, low fire about 47 secs.

There has to be a way to see for sure unless I zero my filter minder on the stat, take an exact reading then let it run for a few day like this then see.

At any rate IF Jm is right it doesnt matter,he said I would have the highest gas bill on the block and use 40% more gas with a 2 stage firing at low whih again is where mine seems to run...

Thank you for trying to help me

Gee dude. That sucks.

[beenthere]

It would be like putting a 2-cylinder engine in a van and expecting to get better milage because you drive slow. The weight of the van doesn't change.

Funny you should use that anology.

A tune up shop near me. Does't engining tuning to factory specs(not the PM tune up most of us are use to).

He does a dyno test on each one.
It took 56 HP to get a mini van that weighed XXXX pounds(don't remember the exact weigh) at 55 miles per hour on the dyno.
He said on the road, it will take more though, due to wind resistance.

The van weight didn't change, but the HP required to do the work in real life conditions did.

PS: His average charge for one of these tune ups, was $650.00, and thats not a typo.

[beenthere]

At any rate IF Jm is right it doesnt matter,he said I would have the highest gas bill on the block and use 40% more gas with a 2 stage firing at low whih again is where mine seems to run...

Thank you for trying to help me

I respect Jim.

But don't buy everything he says.
There are too many 2 stage furnaces saving money over the 80% furnaces that they replaced.

If it were true that a 2 stage 90% furnace is only 40% efficient in first stage.
Then the 80% furnaces they replaced would have had to of been less then 30% efficient by the savings that people see.

Next, you can't use a set run time to calculate how much fuel you will use.
Since your not on a set time for it to go to second stage, or shut off.
Your stat uses temp differencial for operation, not time.

[Jim Davis]

I respect Jim.

But don't buy everything he says.
There are too many 2 stage furnaces saving money over the 80% furnaces that they replaced.

If it were true that a 2 stage 90% furnace is only 40% efficient in first stage.
Then the 80% furnaces they replaced would have had to of been less then 30% efficient by the savings that people see.

Next, you can't use a set run time to calculate how much fuel you will use.
Since your not on a set time for it to go to second stage, or shut off.
Your stat uses temp differencial for operation, not time.

I said a 2-stage furnace runs less than 50% in low fire. Most 80% furnaces run less than 65% in the field in high fire so yes even a 90% will save money over them no matter how bad they run, but not the 40% that people should be seeing. Efficiency is efficiency regardless of run time. CFM X Delta T tells us how many btus are being delivered to the air. Look at the input and the efficiency is easy to calculate. One must measure static pressure in order to use the manufacturers blower spec sheets.

[hvaclover]

Been I ain't the sharpes knife in the drawer, but I do enrgy audits for my customers comparing the energy consumption over a three to five year period.

It's diffacult cause you have consider rate increases and the amount of cold days in one year vs another. In every case our installs have brought down the gas bill on average of 35%,

I was going to get into combustion testing but I have not been able to get an anser from Jim Davis on a basic fundemental: If you test a furnace and the reading are off how do you make adjustments since there are no more air shutter on burners thede days.

[Freezeking2000]

Based on what I have read on this subject if you have an uninsualted and leaing duct system located outside the conditioned space you will have trouble with a modulating furnace using more fuel than a conventional furnace. If the same duct system is in the basement the leakage wold help heat the home. I still do believe a new or a tight duct system, properly installed with r-6 or r-8 insulation is a great fit for a modulating furnace. I think this could go with a retrofit to a dual fuel system as well since the run times will be increased. We do have to do a better job selling duct sealing on modulating and dual fuel applications.

[cvcman]

Ok Rheem told me that seeing as how I am running a 2 stage stat and if the temp drops 1 deg and fires the furnace it will fire in low stage and will NOT switch to hi unless it sees the temp drop while in low and he said i doesnt matter how long it runs even IF it doesnt raise the temp even 1 deg it will run forever in low stage.

Now I have read here that after so many minutes it will go to hi. He said it will not unless you are running a single stage stat???

Who is correct

[beenthere]

Ok Rheem told me that seeing as how I am running a 2 stage stat and if the temp drops 1 deg and fires the furnace it will fire in low stage and will NOT switch to hi unless it sees the temp drop while in low and he said i doesnt matter how long it runs even IF it doesnt raise the temp even 1 deg it will run forever in low stage.

Now I have read here that after so many minutes it will go to hi. He said it will not unless you are running a single stage stat???

Who is correct

Your furnace isn't using the timer, so it depends on your thermostat. On what criteria has to be met to go to second stage.

[mayguy]

it will fire in low stage and will NOT switch to hi unless it sees the temp drop while in low and he said i doesnt matter how long it runs even IF it doesnt raise the temp even 1 deg it will run forever in low stage.

Who is correct

He's correct. On mine when we get say -15˚, the furnace will run non stop in 1st stage, and the t-stat will cycle into 2nd stage as needed.

A couple of years ago, we had 3-4 days of -20˚, and the furnace never shut down. (Had t-stat on Hold)

[cvcman]

sorry I guess im going to 2 diff posts again... So that being said me having a 2 stage furnace is a waste it will always run in low stage unless its after a set back. this is crap man they never told me this and I am not happy to say the least !

[beenthere]

Been I ain't the sharpes knife in the drawer, but I do enrgy audits for my customers comparing the energy consumption over a three to five year period.

It's diffacult cause you have consider rate increases and the amount of cold days in one year vs another. In every case our installs have brought down the gas bill on average of 35%,

I was going to get into combustion testing but I have not been able to get an anser from Jim Davis on a basic fundemental: If you test a furnace and the reading are off how do you make adjustments since there are no more air shutter on burners thede days.

Gas pressure, and blower CFM are what you have to adjust.(there are a few other things, but not in this open forum).

Keep in mind, that the longer the flue and vent pipe are, the less air the induce can draw in, that effects combustion efficiency. So you adjust the gas pressure to compensate for the flue and vent pipe.

Also. You need to adjust the CFM for temp rise. Too much air, and you cool down the HX too much to get good heat transfer. Not enough, and you get a real hot HX, but put more heat out the flue then needed.

The install manual might say x.x" manifold pressure for first stage. But that is based on xxxx BTU per CF of gas. And many areas have more, or less BTU content then the manufacturer uses for their test. So you may have to adjust it up or down a couple tenth of an inch to get proper rise.


AFUE, and SSE are not the same thing.

[beenthere]

sorry I guess im going to 2 diff posts again... So that being said me having a 2 stage furnace is a waste it will always run in low stage unless its after a set back. this is crap man they never told me this and I am not happy to say the least !

No its not.

You are just getting too much conflicting info, and worrying about more then you should.

And, I believe we did say that 2 stage is for comfort, in your post before you got your new furnace.

Relax. Use it set this way for a few months, and see how it works. You may be far more pleased with it then. Right now, your worring too much, to be able to be happy with any explanations you get.

There are stats that can forse it into second stage by time.
EG: After 20 minutes if stat is still calling it would go to second stage.

A lot of people like that, and a lot don't.
The ones that don't like it, don't like when it goes to second stage for 1 minute and then shuts off.

You have an efficient comfort system.

Enjoy it. Don't get tunnel vision on numbers. They can lead you astray, in how your system will really operate.