Single stage vs. dual stage furnace

[Harry Muscle]

I'm in the process of deciding which furnace to get to replace my existing furnace which is ready to die. I've been told that high efficiency furnaces are not really worth it since they cost more up front and they cost more in repair costs in the long run so in the end high efficiency vs normal efficiency will have cost about the same, but the high efficiency will have broken down more often due to it's complexity. This makes sense ... but I have one more quick question. Are dual stage furnaces quite complex and prone to break down also?

I've thinking of maybe getting a 80% dual stage furnance which would be a bit more efficient than a single stage 80% furnance. But I'm wondering if it's worth it. Would a dual stage 80% furnace be as complicated as a 90%+ furnace? Are the parts just as expensive to replace/repair as a high efficiency furnace? Or in other words should I stay away from dual stage furnaces for the same reason I would stay away from a high efficiency furnace (high repair costs, higher chance of break down).

Thanks, Harry

[Phil Scott]

Id go with a single stage 80% furnace myself.

If you really want to save money install two systems...one for the night time sleeping areas, and for the day time living areas... install set back thermostats on each system so the HVAC gets set high in bedrooms during the day, and the living areas get set low at night (these settings can be easily overridden when needed)

If you want to save more money, fit matress warmers to your beds, and you can set the temp to 50F at night no problem.

Be sure to undersize both systems slightly..they operate more efficiently when maxed out.

Install the furnaces in places where they can be yanked out with great ease so maintenance is not a problem. Insulate the ducts well, tape all the seams and flanges well, use duct seal in a caulking tube.

Rheem makes a pretty good unit these days. but brand is not as critical with furnaces as with some other items.

Phil Scott HVAC contractor/ mech engineer since 1911

>

[trader4]

"If you really want to save money install two systems...one for the night time sleeping areas, and for the day time living areas... install set back thermostats on each system so the HVAC gets set high in bedrooms during the day, and the living areas get set low at night (these settings can be easily overridden when needed) "

How exactly does this save him money? I would think the initial outlay for two seperate systems in a house that typically would have only one would be impossible to recover in reduced operating costs. Where is this savings supposed to come from? And in my house here in NJ, if I set the temp to 50 at night, the house would never get there, because a house with decent insulation won't cool off that fast.

[Todd H.]

[lots of great stuff]

Whoa. Now, born in 1911 I can buy (and gospeed to ya as you approach the centruy mark), but being a degreed engineer since 1911...I'm having a tougher time with comprehending since that'd put you in the ballpark of being 2006-1911+21= 116 years old?

If so, you need to tell this young pup that he's no longer famous!

Best Regards,

-- Todd H.

[Phil Scott]

Yes, I am very old... and still flat tracking too.

My goal in life is to be the worlds oldest flat tracker....

lately Ive been working out at Golds Gym and have stopped lying, now I have to beat the young women off with a stick...its a magical combination.

Phil Scott

[Chas Hurst]

A friend just installed a new gas dual stage furnace to replace his oil fired unit. I looked it over before installation and the the dual stage as I saw it was confined to the heat exchanger. There was a large pipe unfinned section and a second section that look like hydronic baseboard. I fail to see how this adds complexity, but readily see how it adds efficiency. The furnace cost $1076, how much money can be saved on a furnace that is at least 10% less efficient?

Chas Hurst

[Bob]

Your goal in life should be to go back to school and learn why removing one entire system and installing two heaters and duct work systems is not cost effective. Either that, or go back to school and learn how not to be a troll.

>

[Phil Scott]

no need to be a vicious jerk in your remarks.... I was clearly defining a range of options.. good ones a that.

On the cost effective issue you would be entirely correct in a temperate climate...and entirely incorrect in a cold climate.

Thats thing with being vicious...it blinds such people to the broader range of life.

Phil Scott

[Phil Scott]

The gas valve and burner assembly would also have to be staged.. that would add some complexity.

Cost effectiveness would vary...in a very cold climate with the furnace running a lot it would probably be cost effective...in the southern states, near the coasts it probably wouldnt be.

These days, we are running short of technical talent... my view is that the simpler it is the easier you can find someone to work on it... exceptions of course.

Phil Scott

[m Ransley]

An 80% single stage is as efficient as 80% two stage, both are Afue rated 80%. A 80% 2 stage is not much less complex then a 90%+ condensing furnace. 80% is someting you buy if you live in a warm area and don`t heat often. Many makes have 94.5% efficient units. The savings from 80 -

94.5% is 18% not 14.5%. So ask yourself and run the numbers first, would you benefit from 18% reduction in your Ng bill. Now think in 5-8 years NG prices may be double. Run numbers with 18% and 10% increase per year in Ng costs, I think you will see high efficency is the way to go. Reliability, many companies offer 10 yr warranty, you just need to ask. High efficiency with VS DC motors save winter and summer apx 30- 50% on electricity used for the blower, I figure at todays electric rates that is apx 100 a year for me, So with a 10 year warranty there is a paybck and good reason to buy the best offered, you cant just look at potential issues or figure 10% savings. With 94.5% and VS DC you are near 20% savings. I havnt even gone into increased comfort winter and summer with VS DC, but I think anyone using an 80% furnace in a high heat area has really missed the boat in many ways.

[Bob]

Telling you to go back to school is not vicious. If you truly believe what you said about changing to 2 heaters, then you need more education. What you said was ludicrous. I don't care if someone lives in Alaska, the payback on something like that would probably take at least 100 years. The cost of removing one entire system, including drywall, ducts, heater, etc. and replacing it with two complete systems it astronomical (not to mention the mess). The heat loss of the building will remain the same, so the payback would be very small.

>> >

[Harry Muscle]

Thanks for that info. I've done some quick math and I'd probably save maybe $150-200 a year with a 94.5% unit. Meaning it would probably take me 5 or so years to recover the initial extra cost of the unit. Unfortunately most of the units I've been looking at only offer a 5 year parts warranty (1 year labour). So after 5 years I've brocken even assuming I haven't had to pay labour for anything yet. After those five years as long as the unit runs fine I'll be ahead, but just one breakdown every two years or so and I'll be breaking even again (assuming the average call of a breakdown is $300 ... especially if it's late at night ... which is usually the case, isn't it :)). Hence my hesitation to go for a high efficiency unit.

Harry

[KLS]

My experience with furnaces of this decade is that they're quite dependable. I'm running a two-stage 94% efficient York (Diamond 95, I think) furnace, installed in April 2003 that has saved us quite a bit of money on the gas bill. Just from memory, my monthly budget outlay for both gas and electric now is $210, and this includes running the central AC installed at the same time as the furnace, whereas the old

1963 Williamson behemoth that preceded these two units (no central AC with this), ran the monthly budget to about $265 (and remember again, no AC), and that was in 2002, before the natural gas price hike. So, I'm very pleased with the cost savings and the efficient heating of this furnace, and I'm in western New York, the same climate as you.

I really would recommend you consider a two-stage high efficiency furnace. I did NOT get the variable speed fan because of my concern about these breaking down, however. That saved me a little $$ on the initial outlay.

[m Ransley]

Ask for a 10 yr warranty many brands offer them

[Harry Muscle]

How much extra do they usually charge for the extra warranty? Obviously it probably depends on the brand, etc. ... but anyone know the ball park figure?

Thanks, Harry

[barry]

'nuther net-nazi.

Encourage diversity of views.

J

[barry]

Once again, assume that energy prices will continue to rise. Soooo, if it looks good now for five-year payback, it WILL be much quicker than that. Enjoy it.

Any objective long-term energy prognosis makes it simple- you can't have too much efficiency. Unless you've money to burn.

J