Heat Hump or A/C

virginia16June 16, 2012

We have decided on the Carrier 58CVA090-16 furnace and have the option of either the 24ANB736 a/c or the 25HNB736 heat pump. The heat pump will cost $700 more than the a/c. The saleman gave ua a operating cost estimate that showed significant savings with the heat pump, but the gas cost was estimated wrong, at $1.70/thrm. Over the past year our gas bills ranged from $.96/thrm to $1.39/thrm. Our electric is $.12/kWh on avg. I am thinking of just staying with the a/c if the savings won't be that substantial. We have two units and our upstairs unit is still working so I am trying to envision savings when the heat pump with only be used on 2/3 of the living area. This system is for approx 2,900 of living area (main level and finished basement). We could stay in this house another 10-15 years, we have no current plans to move before then. Any suggestions on which to go with?

Also, we have the option to instal a carrier LFP1418 humidifier for $600. He talked about the technology being different now (we have a 14 yr old Honeywell by-pass humidifier.) Is this a good price?

Lastly, the furnace that everyone has suggested for us is 90,000 BTU. We are replacing a 70,000 BTU furnace. Both 80% eff. This salesman said that he was bumping up to 90,000 so the system didn't have to work as hard. Is this a proper recomendation?

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"Lastly, the furnace that everyone has suggested for us is 90,000 BTU. We are replacing a 70,000 BTU furnace. Both 80% eff. This salesman said that he was bumping up to 90,000 so the system didn't have to work as hard. Is this a proper recomendation?"

ABSOLUTELY NOT!!! Assuming that the 70,000 unit is the proper size (how long does it run on the coldest days?) the 90,000 unit will produce close to 30% more heat. This will result in more frequent, shorter heating cycles and greater temperature swings (read: less comfortable), which will be MORE waring on your furnace.

If your current furnace also runs frequent short cycles, you most likely will benefit from a smaller furnace.

An accurate heat load calculation will determine actual heat and cooling losses.

Your location information would be helpful. What is the tonnage of your current air conditioning unit?


    Bookmark   June 16, 2012 at 7:28PM
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I assume you are in the South.

Dual fuel will save some money at $1 a therm and $.12 a kwh with that equipment. How much - I'd say about 15% WAG. Assuming your house is reasonable and you live in the South, that maybe $100 a year. That may be a good payback for you or it may not.

In the end, electricity has a more versatile origination so should have more stable pricing. "Should". No one knows but being diversified has its advantages.

I live in NC, have a 90% NG, Seer 16 system and very cheap heat. I set my crossover at 40 degrees with $.80 therm and $.10 KWH.

    Bookmark   June 17, 2012 at 6:22AM
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I am located in the mid-atlantic region, in Northern Virginia. We are replacing a 3 ton a/c unit. Why has everyone automatically recommended the 90,000 btu furnace? Is it more expensive than the 70,000 version, giving them a higher sale?

    Bookmark   June 17, 2012 at 8:20AM
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If current 70 K furnace performed to your satisfaction, then certainly the new 70 K model will as well. See no reason at all to go up in size but this idea of more is better is still typical for many dealers. Basements at or partially below grade have very small heating and cooling loads.

Dual fuel systems were more popular not so any years ago when one could leverage electric versus nat gas. Not true today because of the decline in nat gas rates and the continued upward climb of electric rates.

I ran some fuel comparisons using both low and high range nat gas rates on 80% eff furnace. Clearly the low range of nat gas rates is not beneficial for a HPx; the high range is though.

Unless there is some installation related issue, I would look at the high eff 58MVC060 60 K 95% eff furnace paired with the AC condenser.

Regardless, you will need the Infinity controller which I hope the dealer included in his quote. New lineset and box media filter cabinet should also be part of the quote.


    Bookmark   June 17, 2012 at 8:50AM
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I just read David Cary's post. Using your low end rate for nat gas, clearly HPs are not beneficial on an operating cost basis. Plus there is the life of the equipment to consider. As is universally accepted, a good furnace has a longer operating life than a condenser. I would spend my $$$ on an upgrade to the high eff furnace that I suggested. A much better choice than the HP upgrade.


    Bookmark   June 17, 2012 at 9:13AM
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The price difference between a 70K and 90K BTU furnace is small. If your 70K BTU furnace has worked well in the past the, the new furnace will work just as well if not better.

The claim the smaller furnace works harder is nonsense. A large furnace which short cycles works harder in my opinion since it is frequently turning on and off. You will find an oversized 2-stage furnace will run most of the time in the low stage.

Do you think you need a humidifier? How dry does it get without using the humidifier?

    Bookmark   June 17, 2012 at 12:06PM
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Tigerdunes - it isn't really fair to just use the low end rate. Wouldn't average be better. But I don't disagree with your point. I do wonder what you put if for a COP? I assume that above 40 degrees would be about a 4 for his equipment. I am in a similar climate and more than 1/2 the heat is above 40 degrees.

$700 is not bad for the versatility.

North of here, 80% is a dinosaur. Even here 80% is a dinosaur. I'm guessing there are install issues.

    Bookmark   June 17, 2012 at 5:54PM
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When I inquired about higher efficiency furnaces I was told installation would cost an additional $2k, to run the piping, etc. I never got an official quote but figured at that price range it wouldn't be worth it.

    Bookmark   June 17, 2012 at 7:57PM
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What are your usual winter heating bills?

    Bookmark   June 18, 2012 at 5:36AM
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Tigerdunes - it isn't really fair to just use the low end rate.

For DavidCary

What's not fair? The country is awash in nat gas and at this moment we are on the low end of nat gas pricing. Do you have a crystal ball that tells you future pricing of oil and nat gas? Now electric rates are an entirely different matter. They are regulated and prices are not marketplace driven like nat gas and oil. And yes I do include oil although the marketplace
seems rigged. Electric rates continue on an upward rise and usually way above inflation rates. Surprised that most citizens have not raised hexx about it.

As I've said in the past, I have a DF system so this is something I know a little about. And making a comparison between fuel operating costs. Last heating season, I estimate I used about 50 therms for heat while my Trane HP did the yeomans work practically the whole season. The leverage between the fuels has all but disappeared. Now if nat gas prices take a sharp rise, then that would change the metrics altogether.

Just in the equipment side, Carrier's Greenspeed seems to be the leader in new HP technology. Not certain what the demand is for those condensers either in a DF or all electric configuration. Of course everyone in the industry was watching carefully the Hallowell story. The promises seemed much greater than the reliability and results. And we know what happened to them.

And finally, you seem to question my methodology. I used. a COP of 3 which I believe to be both generous and realistic. If one over promises, usually disappointment occurs especially if one is looking for a ROI which I think is generally a poor approach in justifying new HVAC with high
efficiency. Let's face it. HVAC is a necessary evil. You want to be cool in the summer and warm in the winter. I would like to see a more balanced approach that can justify both reliability and longevity.


    Bookmark   June 18, 2012 at 7:30AM
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This past winter was unusually mild; our bills ranged from $150 - 200 (and only had substantial heat usage over a 4 month period - paid $765 during that period). The winter before that we had an unusual stretch of frigid weather and we had two months of $300+ bills (paid $1,125 over 5 month period). Our summer gas bill ranges from $25 - $35. And also to note that this furnace is for the main level and basement, we have a separate unit for the upper level (14 years old but still runs fine) so this upgrade will only be for 2/3 of the house (I realize that the downstairs level is the heat workhorse)

    Bookmark   June 18, 2012 at 1:56PM
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I guess I would probably use 3.5 if you set your crossover at 37 degrees. At 37, 3.5 is a reasonable estimate without knowing specific equipment. Since that is your lowest temp, the COP can only go up.

While the COP is not published, I suspect the COP at 45 degrees is above 4. Since that is actually the mean temp that the HP will see, you could argue for using 4 as a COP.

NG will rise. There is absolutely no question about that. I don't think it makes sense to base a decision based on the nadir of a fuel's price. Sure we have a lot but it will get used for other things soon enough. Electricity will always be more flexible. If NG is free, then electricity becomes nearly free. They are building 3 new NG plants in NC over the next 5 years. Why - because it is now cheaper than coal.

Every truck fleet could be NG in 5 years. They will never run on electricity.

I've paid $.10 a kwh for the last decade (give or take a penny).

Sounds like a 90% would be worth $2k if you stayed in the house a while. What looks like a 20 year payback, comes to lot less if you factor in probable high energy price inflation.

    Bookmark   June 18, 2012 at 8:52PM
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