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  1. #1
    Join Date
    Mar 2012
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    1

    Smile Heat Pump vs. Gas Furnace

    I recently bought a foreclosure that is a post WWII home. The home has a naturl gas fired central furnace that will need to be replaced soon and the A/C cond. unit outside was installed in the '70s. We insulated all of the walls of the house and the attic has about 16 inches of a combination cellulous and fiberglass blown in. I plan to replace the double pane alum. "not too great" windows with a higher performing vinyl. I live in North Arkansas where we pretty much had no winter this year. But, some winters bring ice storms, snow and temps below 28 degrees. QUESTION: should I get a heat pump or a natural gas fired furnace when I take the plunge??

    Thefabulousmrfixit

  2. #2
    Join Date
    May 2011
    Posts
    251

    Default Re: Heat Pump vs. Gas Furnace

    You could do both and go dual fuel. It will depend on your electric rates. Usually above about 40F, the heat pump is a little cheaper to operate. Below 35F in most all areas, the furnace is cheaper.

    Heat pumps & AC need proper airflow so as with furnaces, proper sizing is important. Most people have oversized equipment. IT's less efficient and less comfortable (Larger temp swings). IF you've added insulation, you likely don;t need as large of a system as your current one.

    You're far enough south that you might just go with a vairable speed blower, but still 80% furnace and pair that with a heat pump. THE furnace will provide more comfortable heat below 35F and the heat pump will be cheaper to operate above that and will rarely go into defrost.

    Also, a furnace is easy to back-up if the power goes out. Just a small 2000W inverter generator will be enough to run the furnace, or a single small window AC or refrigerator or microwave... just one at a time. Running the whole heat pump will require a very large generator.


    I had dual fuel system in my last house and really liked it... if the contractor had sized it properly. I've since learned a LOT about HVAC and "seen the light" I guess you could say. It's also now a major part of my position at work.

    I will say that the furnace definitely provides a warmer, more comfortable heat. The heat pump neeeds a lot of airflow so discharge temps are a lot lower. SO you get a lot of air movement. The furnace on low stage was silent. SO a 3 ton heat pump for example paired to a 45k BTU furnace will need 1200CFM for cooling or heating on the heat pump. But the furnace on a normal 50F temp rise on low stage will only need about 550CFM. That's going to be completely silent in comparison. In your climate, you won't need a very big furnace. You design temp is probably something like 15F. SO a heating system in Arkansas will be as much as 25% smaller than a system than lets say northern Missouri. But the AC system might be 5-10% larger.
    Last edited by motoguy128; 03-10-2012 at 09:08 AM.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  3. #3
    Join Date
    Nov 2011
    Posts
    51

    Default Re: Heat Pump vs. Gas Furnace

    My advice is to go with either a geothermal heat pump (if your geographic area permits it) or a hydronic system.

    Having a hot air furnace is just fine, but they provide a poorer quality of heating since air is not as efficient at retaining thermal energy as water. A hydronic system is basically a baseboard hot water system, or a radiant in floor system. Either way, air handlers can be installed for a mixture of hot air/baseboard/and AC.

    Air handlers, in case you don't know, are like hot air furnaces except the heat source is a hot water coil. A specific hot water zone could be an air handler, opening up the possibility for AC.

    Go with the heat pump if you can't do a hydronic system.

  4. #4
    Join Date
    May 2011
    Posts
    251

    Default Re: Heat Pump vs. Gas Furnace

    Geothermal has a huge outlay and is only cost effective because WE... as taxpayers subsidize 1/3 of the costs. There's plenty of maintenance with ground loops, circulators and it's still just heat pump.... not a magic box. I've heard a TON of horror stories with this equipment only lasting 5-7 years and costing $10k to replace the heat pump. OH... any you have to dig up your yard... and 20-30 years from now if a pipe springs a leak, you have to dig it up again.

    It's somewhat unknown that you aften need to flush the loops annually to reduce microbe growth.


    Hydronics are superior in most ways. That's why they were so popular for a long time. But guess what? They cost more, that's why they went out of favor. Even with hydronics, unless you install a chiller, you'll still need AC.

    I think Geo is great for new construction in a well insulated home and the best choice when you have a lot of land and no access to natural gas.

    Oh, and if you're a tree hugger, natural gas has nearly the same carbon footprint as geothermal. Actually a system like a Carrier Greenspeed Hybrid dual fuel system has a smaller footprint. Newer inverter driven heat pumps are nearly as efficient as geothermal with a lot less complexity.

    If we really cared about reducing the use of fossil fuels, we'd offer the same 30% credits on air source inverter driven dual fuel systems like the Greenspeed and soon to be released equipment form other brands.

    It's sort of like old wood windows vs. new ones. IF I can get 70-80% of the efficiency by just adding a storm window, then the payback of that incremental 20-30% has a tremendously long payback.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  5. #5
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,722

    Default Re: Heat Pump vs. Gas Furnace

    I like a gas furnace in my area, Maryland, because they are much more comfortable than heat pumps in the winter as well as cheaper generally because of the typical resistance backup used.
    That said it, sounds like a heat pump, even with electric resistance backup may me a good solution for your climate. I would still consider an a/c unit & gas furnace. New furnaces with electronics can be sensitive to dirty power, so using a cheap generator to power it up could cause problems. I'm not a big fan of geothermal because of the initial cost and complexity of the systems, but it will undoubtedly give you lower heating & cooling costs. You may need to upgrade the electric service if you go heat pump with electric resistance backup.
    Even with the barely winter we had here, we still had plenty of days in the mid to low 20's, not good for heat pumps.

  6. #6
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Heat Pump vs. Gas Furnace

    Quote Originally Posted by Thefabulousmrfixit View Post
    I recently bought a foreclosure that is a post WWII home. The home has a naturl gas fired central furnace that will need to be replaced soon and the A/C cond. unit outside was installed in the '70s. We insulated all of the walls of the house and the attic has about 16 inches of a combination cellulous and fiberglass blown in. I plan to replace the double pane alum. "not too great" windows with a higher performing vinyl. I live in North Arkansas where we pretty much had no winter this year. But, some winters bring ice storms, snow and temps below 28 degrees. QUESTION: should I get a heat pump or a natural gas fired furnace when I take the plunge??

    Thefabulousmrfixit
    You've made a good decision with the insulation and window upgrade to begin with. This will make the home more efficient and will reduce your heat/cooling costs.
    I'm partial to the setup you already have and with the upgrades to insulation and windows you may find a cost saving in needing a smaller sized furnace and A/C.
    Replacing the equipment with the same type will actually be more cost effective since there won't be any additions or modifications.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #7
    Join Date
    May 2011
    Posts
    251

    Default Re: Heat Pump vs. Gas Furnace

    In your climate, I would look at a 80% efficient furnace with a variable speed blower for more efficient AC operation. You could consider dual fuel if you have very low electric rates or can get an extra rebate from your electric utility. Above about 45F< heat pumps are cheaper to operate than gas furnaces.

    A condensing 90%+ furnace in your climate won't have a payback unless you have a very large home. The increased installation costs and equipment costs with few heating days is a waste of money.

    I think same thing with replacement windows. For 1/3 the cost, you could have installed low-E storm windows and gotten 95% of the energy savings in a warmer climate. IN warmer climates, energy efficient windows make less of an impact. Low-E makes that larger impact in the summer. R vale matters more in winter.
    1925 Two-Story Stucco Beaux Arts Neoclassical

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