2 stage vs standard gas furnace

[shaum76]

How much more efficient are 2 stage units compared to standard units?
What's the usual payoff period for them in a moderatley cold area like Delaware

[BaldLoonie]

2 stage furnaces are for comfort, there is no efficiency gain.

[shaum76]

i was told by contractor that 2 stages give you a good boost in efficiency without upgrading to the next AFUE.
he also said the variable speeds are the ones that are mostly a "confort" factor than efficiency

[Panama]

Contractor is wrong.

[shaum76]

is there a saving on "heating bill" in upgrading to a 2 stage.

[dash]

No saving,just comfort,for two stages.

Variable speed fan ,comfort and likely some savings on electric for the fan.

[cg2]

Some people even say that you lose efficiency on low fire.

[beenthere]

Originally posted by shaum76
i was told by contractor that 2 stages give you a good boost in efficiency without upgrading to the next AFUE.


If it gave an efficency boost, then it would have a higher AFUE rating.

[Panama]

Originally posted by cg2
Some people even say that you lose efficiency on low fire.

Yes. Excessive combustion air reduces efficiency.

[wallynut]

If a home has a heat load net 50,000 btuh, that means that amount of energy is needed in extreem conditions ( 0 degree
and maitain 75 to 80. More than 80% of the time you do not see
those temps in New England. (I live in Mass.)So if you have a two stage unit which is 40/60 input it only makes sence to me that running on 40,000 btu input would be a very good thing.

[heatpumpguru]

In Delaware we found that it makes the home alot more comfortable,due to longer run times,not the BIG BLAST and then OFF and then on again.Some of the places in Wilmington we have taken out the eletric baseboard in some rooms that needed them with the old heaters.

[browntigerus]

> it gave an efficency boost, then it would have a higher AFUE rating.

May be I am wrong, but the only scenario I can see how 2 stage can provide boost in the efficiency is in combination with zoning system, when small zone calls low fire.

[wallynut]

If you have two same 92% furnaces side by side and the single stage is 50,000 input , The two stage is 35/50 input you tell me which one will be more efficient operating for a season. ( More efficient meaning will burn less fuel for that
season)

[docholiday]

Remember burner efficiency is not the issue, its input versus output and ultimately there is very little difference. The 2 stage, as we all agree, is for comfort, and we would then have to ask what value you put on additional comfort.

[Chill]

They will both burn the same amount of fuel.

Now, if you compare a 90 two-stage and a 90 single stage, which one is more effient?

[Chill]

I agree that the two stage is for comfort, since the manufacturers only rate the two stage, one or two points higher than single stage.

[jacob perkins]

I think 2 stage is more efficient.(or i wouldnt butt in here)
Longer run times throughout the entire heating season ,and not just on design days, are one reason.

Or am I thinking weird?

[docholiday]

Yes, you are thinking weird, that would be a comfort issue not an efficiency thing. Your system, regardless of stage will provide the correct amount of heat by burning the same amount of gas over the course of time. Its a matter of burning a candle at one end or both, either way the same amount of wax gets burnt when the candle is gone.

Now, one could argue that longer run times require the blower and inducer to operate more and therefore a slight cost increase for running motors could be considered. Again the difference here is in comfort or ability to stay at set point versus cycling using and having swings between a call for heat and the end of a cycle.

[jacob perkins]

/

[Edited by jacob perkins on 10-19-2005 at 09:46 PM]

[jacob perkins]

Originally posted by docholiday
Again the difference here is in comfort or ability to stay at set point versus cycling using and having swings between a call for heat and the end of a cycle.

that was my point,cycling is less efficient.
ignoring electric.

in a region like new mexico ,texas ,or tennessee where winter temps are wildly unpredictable,with the issue of cycling and (oversizing for a few days of the year)the two stage is more efficient for the reason you stated.

[wallynut]

If you think both 90% units would consume the same amount of natural gas (single stage and two stage)in the same season even if the two stage ran 80% of the time on low fire,
than using that analogy the 35/50 input would consume
the same amount of fuel to heat the home for a season as
a 75,000 btu 90% single stage unit right? "WRONG"

[fat bob]

I like the 2 stage because it is much quieter on low stage, and runs on that stage most of the time.

[Carnak]

The inducers are not two speed?

Longer run times would save energy, each ignition cycle wastes energy as it warms up to steady state.

[wyounger]

Originally posted by Carnak
The inducers are not two speed?

Longer run times would save energy, each ignition cycle wastes energy as it warms up to steady state.

All that stuff is already considered in AFUE. It is a "big picture" rating.

[Wirenut]

The Inducer fans ARE two speed, or at least the one on my Lennox furnace is. I can tell you that comfort is a major reason to go with two stage units. I have had mine for several heating seasons and am very happy with it. Insist on a two stage thermostat, don't let someone tell you the built in timer in the furnace will take the place of a good two stage stat!!

[Chill]

Originally posted by wallynut
If you think both 90% units would consume the same amount of natural gas (single stage and two stage)in the same season even if the two stage ran 80% of the time on low fire,
than using that analogy the 35/50 input would consume
the same amount of fuel to heat the home for a season as
a 75,000 btu 90% single stage unit right? "WRONG"

Is the 75,000 over sized or undersized? Why compare such an un-realistic situation?

[dpatty]

I would agree with carnak on this, the longer run times and fewer start cycles would be more efficient. I would also consider for the same reason that the furnace would probably last longer due to less stress on the heat exchanger.

[Carnak]

If it is a comfort issue then forget the two stage and get a rheem mod :)

[wallynut]

The 75,000 is more than you need But so is the 50,000
input on the two stage 80% of the time.
Get my point?

[wallynut]

Comfortmaker also makes two stage with two speed inducer and two stage gas valve, not modulating. (Model C9MPT050F12)

[jacob perkins]

maybe they say that for a reason.

so people wont think that they should down size their furnace because it is "more efficient" two stage.

[Carnak]

I think a lot of two stage out there hardly ever hi-fires.

The furnaces seem to be over sized, some times intentionally to get enough air for AC.

The two stage is like a safety net for oversizing.

I guess my reason for saying this was the most common furnace sizes I sold in Canada were 60 & 75 MBH, and designing for close to 100F temperature differential.

I see all kinds of posts in here on furnaces 100 & 125 MBH, in a much warmer climate.

[Edited by Carnak on 10-22-2005 at 03:19 PM]