Hello,
Having a dual fuel system can help your worries about cost to operate, but normally a heat pump uses backup electric heat. As to replacing the plenum, look for a system that is the same height as the existing system. Nodifying a plenum is commonplace in my area. Newer systems are smaller. The newest variable speed high SEER systems are also different.
You will need ned wiring when installing an electric heat furnace. Depending on gas prices, this can make sense. Get more bids.

Chris

First choice is high eff heat pump with var speed air handler. Trane/AmStd make great heat pumps but Carrier/Bryant are the best overall system with their sophisticated controls on the Infinity/Evolution models. Go with 2 stg models for the best operating efficiencies.

Second choice would be dual fuel. Not certain a 92+% AFUE gas furnace would be a good economic choice for your area/climate.

I would include a good whole house air filter cabinet. And I would definitely want some better understanding/documentation for the new 220v power line. I suppose dealer is saying this is necessary for the heat pump/air handler model. Correct?

IMO

Thanks for the quick responses.

So, in your opinion, I would be better off going with a heat pump/electric heat strip than with a duel-fuel system? Considering my climate, should I even be concerned with installing an electric heat strip since the heat pump will provide adequate heating most of the time (rarely drops below 30-40f here)?

Regarding the 220v, the contractor says that in order to install the heat strip, he would have to run a 220v line up to the attic. If that's what has to be done, then I'll do it, but when he started rattling off all of the modifications that were needed, it made me re-think my choice to go with a heat pump. It sounds like my original research was correct in that a heat pump is the best way to go.

In your opinion, will the heat pump really be more cost efficient than gas heating? What would you define as "high efficiency"? I was considering a 14seer model, but should I go higher?

Thanks again for you help.

Best Regards,
Chris

Like the OP, we also believe we need a new furnace/AC and have some questions.

I also live in the South, but not as far as New Orleans. I am in NE Georgia where summer temps are in the 90s with similar humidity and winter temps can get down into the teens although rarely. The last few weeks, we have seen lows at night in the 20s and daytime highs in the 40s. My husband and I bought our split-level 1979 house this summer. The A/C works OK (original 1970s GE model), although our electricity bills were high ($350/mo.) and air-quality was poor. We believe there is mold in the ducts (plenum was moldy) and plenty of dust also.

The gas furnace is also the original GE model and the HVAC guy could not get it to work. Apparently the transformer is shot. There is also rust and possibly carbon deposits under the furnace, leading us to believe the heat exchanger MAY be cracked. At this point we are leaning towards a whole new system, with new ductwork. Is it worth getting a second opinion on the existing ~30 yr old furnace, or should we start looking at new systems?

We had problems with high humidity and mold in the house this summer. In addition, I have allergies and asthma, so I am concerned about air quality. I am a stickler for checking and changing the filters regularly, esp. with 4 cats!

If we get a new system, should we go for a gas furnace, heat pump or dual fuel? The house is about 1700 sq. ft., split level, with R13 in the walls and single pane windows (we would like to upgrade to Energy*). The main living area is above the enclosed crawl space (under-floor insulation of R15) and the bedrooms are above the garage (currently uninsulated, but looking to put R15-R30 there). All ductwork runs under the floor and is currently easily accessable.

We are paying about $0.85 a therm for gas and $0.09 kWh for electricitry right now.

I would really appreciate your ideas and insight.

Shivering in Georgia!

Bargain

I also live in the Southeast. My advice would be the same as my post above to Chris (levay). High eff 2 stg heat pump with var spd air handler first, dual fuel second.

You should ask dealer to thoroughly inspect your ductwork system as to size, supply/returns, insulation properties, overall condition, leakage test, and address what you describe as mold in your ductwork. If you have any hot/cold spots in your home, this should be looked at as well as this usually is indication of poor ductwork design to that specific area. There are ductwork cleaning services that can be effective but I think that depends on the condition of your ductwork and how extensive the mold issue is.

You mention asthma and allergies with members of your household. Am Std'a AccuClean or Trane's CleanEffects filter might be a good filtration choice for your new system. Obviously, I would not spend any significant funds on a system as old as you describe-a waste of money.

While energy eff windows are nice, I would definitely go ahead and spend the funds to insulate the bedroom areas that you say have poor insulation.

IMO
GoodLucK!

Ok. I researched the current gas and electric rates and did calculations comparing and 80% and 90% gas furnances, electric heat strip, and the heat pump. For my area, it appears more economic to go with the heat pump over gas. Here are my calculations (thanks to a previous poster for the alogithms):

80%
1,000,000 BTU out / 80% = 1,250,000 BTU in / 102,000 BTU per CCF gas = 12.254 CCF X $1.56 = $19.12

90%
1,000,000 BTU out / 90% = 1,111,111 BTU in / 102,000 BTU per CCF gas = 10.89 CCF X $1.56 = $14.16

Resistance
1,000,000 BTU out / 3,412 BTU per KWH = 293.08 KWH X $0.10 = $29.30

Heat pump with COP of 3.5 (47 degrees)
$29.30 cost of resistance heat / 3.5 = $8.37

Heat pump with COP of 2.4 (17 degrees)
$29.30 cost of resistance heat / 2.4 = $12.08

Obviously I begin to loose cost effectivness if I have to use the heat strips, but in my southern Louisiana climate, I should rarely, if ever, have to use the strips.

I highly recommend going to your gas company and electric company's websites and get thier kWH and CCF rates then plug them into the above calculation. It will give you a clear picture of what it will cost you.

If there is something I am overlooking here, please let me know.

Thanks again,
Chris

Yes, make certain you apply all taxes, fuel surcharges
and delivery/user fees into the calculation. Electricity looks
much less attractive when you do.

HTH
Chris

Yes I agree. My original kWH rate was .04 cents! The surcharges, taxes and delivery fees are more then the kWH itself.

Chris

Please explain the different heat pump COPs. I would like to do this cost comparison for my power rates (gas $0.86/therm and elec. @ $0.09 kWh), but I am a little confused.

Thank You!

Bargain,

As you know, a heat pump has two efficiency ratings, SEER for cooling and HSPF for heating. Keep in mind these ratings will be different for the same model due to the size of the heat pump. ie, a 4 ton XL16i's ratings will be lower than a 2 ton XL16i.

COP stands for coefficient of performance and is another effciency measurement for a heat pump's heating output. It is a rather involved calculation but for the average homeowner, you can divide a models's HSPF rating by 3.4 and this will give you a close approximation of a heat pump's COP.

I have attached a little primer on heat pump efficiencies which might be helpful. Generally speaking a COP of 2.75 and above is very good.

BTW, I was looking at your nat gas rate. Does this include all applicable fees and do you mind sharing the name of your nat gas supplier for your area?

Thanks

Here is a link that might be useful: Heat Pump Eff

We pay a $5.75/mo service fee for gas. We have only just started service, and have not yet received a bill. In fact, we should not have used much, if any gas, since the furnace is our only gas appliance and that is broken.

Our natural gas marketer is Walton EMC. I used to have electricity service from them and was very happy with their rates and service. Unfortunately, we do not have an option for electricity in our new home so we have the ever-expensive, dirty coal-fired GA Power! I beleive Walton EMC does a lot of business with Wal-Mart in this area, and has won various awards from them.

Thanks for the calculation info.