Natural Gas Furnace Vs. Heat Pump ?

Discussion in 'Environmental Discussion' started by kenmce, Apr 18, 2021.

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  1. sam spade 2

    sam spade 2 Senior Member

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    An honest HVAC contractor will give you the right answer.......if you can find one.

    IF there are very many days during the winter where the temp doesn't get much above 30F, then the heat pump option probably isn't really good.

    The backup heat source for a heat pump is usually electric which is VERY expensive in some areas.

    The answer might be different for northern NY than for the southern regions but my guess is GAS if it is readily available.

    EDIT: And the answer might be somewhat different since this seems to be some additional new space and not a whole new structure. I think that tilts the discussion even farther toward the gas option.
     
    #21 sam spade 2, Apr 19, 2021
    Last edited: Apr 19, 2021
  2. rjparker

    rjparker Senior Member

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    I thought about responding but decided I will stand pat with my winning hand.
     
  3. Trollbait

    Trollbait It's a D&D thing

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  4. kenmce

    kenmce High Voltage Member

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    To answer more questions:

    Natural Gas is already present at the site.

    Greeness vs cost - I am steering towards the greenest structure that will fit within the budget. If I had an unlimited budget I would use insulated concrete forms, Earth berms, and have a roof full of solar. I don't have an unlimited budget but that doesn't mean I give up and walk away.

    Thorium power not available from my utility at this time.
     
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  5. John321

    John321 Senior Member

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    We have a Carrier Hybrid system- Carrier Infinity Heat Pump coupled with a Carrier 96% high efficiency gas furnace.

    By adjusting the Heat Pump lockout setting you determine when the gas heat takes over.

    I like this systems flexibility. If gas rates go up you can adjust the Heat Pump lockout setting so the Heat Pump will run more in cooler temperatures.

    If gas rates are low you adjust the lockout setting so the gas furnace runs more.

    It give you some flexibility and control over your energy costs.

    With the Carrier Infinity system variable scroll compressor on the Heat Pump and the variable blower in the indoor furnace unit it makes for an efficient package that provides good comfort for the homeowner year around.
     
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  6. fuzzy1

    fuzzy1 Senior Member

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    Here is followup with more detail.
    For the Old-Century dinosaurs here who still believe that air source heat pumps (ASHP) are not useful below +40F, here is a definition for "cold climate ASHP" (ccASHP) from a 2019 presentation:
    upload_2021-4-19_18-57-53.png

    How do these differ from Old School heat pumps? Here is a graphic representation:

    upload_2021-4-19_19-1-37.png


    Here is a representative design chart from a 2019 presentation:
    upload_2021-4-19_18-46-14.png

    With appropriate cold climate products, pick the equipment size based on a desired crossover point, below which supplemental heating from another source needs to be added. The "dinosaurs" here seem to think that crossover point must by 40F or 32F, but in this sample, it can be 19F, or 10F, or 3F. This chart shows how much supplemental heat power is needed for the middle of those choices:

    upload_2021-4-19_18-49-21.png

    While this slide shows the make-up heat coming from electric resistance, it could be something else such as natural gas or propane.
    Looking at a few other combinations, I'm finding COPs of:
    2.2 at -13F,
    2.7 at 0F,
    3.1 at +17F,
    3.5 at +30F, and
    3.9 at +47F.
    While these are for an indoor temperature of just 61F, this seems reasonable for extreme outdoor conditions where I'm dressing with the intent of heading for work or various other activities outside.

    Some different products are rated to operate at -15F and -22F.

    Here is a 2017 Department of Energy presentation where a special project used newer technology to outfit an Ohio home to need no auxiliary heat down to -13F. And a Fairbanks Alaska facility to achieve a COP of 1.8 at -30F, while still putting out 75% of its rated capacity. It may have still needed some auxiliary heat in those conditions, but the ccAHSP was still doing its part. This stuff may not be on the consumer market just yet.
    upload_2021-4-19_19-29-39.png

    One thing to note about operating these systems, it is often best to not set temperatures down much overnight or when away for a workday. With limited heating capacity, they are slow to catch up when the thermostat is pushed back up. During catch-up, the higher heat output, especially at the coldest part of the whole day in the morning, will reduce their COP and may trigger the auxiliary heat. Best performance typically means to just set the thermostat and leave it alone. Leave setbacks for just when the thermostat will be left down for multiple days at a time.
     
    #26 fuzzy1, Apr 19, 2021
    Last edited: Apr 20, 2021
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  7. TinyTim

    TinyTim Active Member

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    It is a modern heat pump, circa 2014-2015. I can tell the difference between heat pump heat and furnace heat. It doesn't run when temps are 55F or higher. I have it set for 40F but I was thinking about bumping it up to 45F. Anything below 40F outside and the gas furnace kicks on. I have the color touch screen honeywell thermostat that only allows changes in 5 degree increments instead of single degrees. The math experts have it all figured out. I ball park things with accuracy just below the math experts. A heat pump should be set to 37-38F if you do not have a gas furnace. It's a $2-3 difference between gas and electric, the latter being the heat pump. I justify the cost of heat pump heat to less dry skin and a more comfortable environment compared to gas heat. When it's cold, gas makes sense because you want a warm house. The house has plenty of insulation.
     
  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Just adding mention: there is a local element to all of this.

    Who is installing your system? What do they know? What are they capable of supporting long term?

    My house was oil heat. The former owner added a woodburner for flexibility. I added a 3-room modern minisplit machine for the bedrooms.

    Now 4 years on from the minisplit installation? I'd like to add them to the rest of the house, based on their performance. However, I would also like to just shiver under a blanket based on what I had to go through to get it installed.

    Due to some oddities of my job, I have seen many, many minisplit systems installed on 6 continents now. I believe in the technology, I trust it. But I'm not sure I ever saw a sketchier or more problematic installation than the one in my own house in Pennsylvania.

    Point is- the "best" system may not be available to you because nobody in your area is any good at installing or repairing it. Consider that well.
     
  9. sam spade 2

    sam spade 2 Senior Member

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    Don't you have anything better to do with your time ?
    I mean REALLY ??

    Most of the comments I've seen fall into the "not efficient" category instead of "not useful".
    And that is absolutely true.
    The efficiency of an air source heat pump for heating goes down as the outside temperature does........at the same time that the heating load goes UP.

    When I built my house in Illinois about 10 years ago, I put in a high efficiency gas furnace (plastic exhaust pipe) and a "conventional" central AC unit. Spending more than that for equipment is often hard to justify or recover over the expected life of the hardware.
     
  10. Trollbait

    Trollbait It's a D&D thing

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    They still sell basic NG water heater tanks along side the blower vented and condensing models. Scions used dirtier engines and older transmission designs. Being new doesn't mean the technology is up to date.
     
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  11. fuzzy1

    fuzzy1 Senior Member

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    Mirror, mirror, on the wall ...
    Everybody already knows that.

    The point here is that the conditions where heat pumps can work and be competitively efficient, keep getting pushed down to include ever lower temperatures, now covering virtually all climate zones in the continental U.S. But there are a bunch of detractors here who are stuck in the old century and refuse to acknowledge the current state of the technology and product market.

    These detractors seem analogous to the detractors of the Prius and other hybrid vehicles one and two decades ago. ;)
    This is an environmental forum. It is not a purely bean-counter forum focused exclusively on today's spot-market commodity prices, to the exclusion of the environmental impacts.
     
    #31 fuzzy1, Apr 20, 2021
    Last edited: Apr 20, 2021
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  12. fuzzy1

    fuzzy1 Senior Member

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    Of course, everyone can, that nature is at the very heart of the beast. Combustion furnaces can produce very high exit air temperatures, and commonly did so to keep the ducts and air handling costs small. Heat pumps inherently must use lower air exit temperatures in order to get efficiency, so therefore must have larger ducts and air handlers. This lower exit temperature is a common initial complaint from newcomers, until they get used to the newer technology.
    That may make beancounter cents at today's spot commodity prices, but it makes no environmental sense. Your gas furnace exhales plenty of CO2 to the atmosphere, driving AGW. But your electric heat pump is driven by a carbon-neutral utility:
    upload_2021-4-20_9-50-36.png

    upload_2021-4-20_9-51-49.png

    Lipstick on a pig?
    That would be for your particular installation, which sounds like it wasn't selected well. That is pure poppycock for my equipment, installed years before yours.
    I don't have gas service at all. So what should I do when outside temperatures go below your expressed setpoint? Turn on my old inefficient electric resistance heat? Just go cold?

    Nope. The heatpump is the better way to go here. And so for much of the rest of the country now too.
     
    #32 fuzzy1, Apr 20, 2021
    Last edited: Apr 20, 2021
  13. John321

    John321 Senior Member

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    Prices for different types of energy are sometimes unpredictable. Years ago Natural Gas prices exploded and many people were looking for alternatives to heating with Natural Gas.

    If a very severe winter comes and people use much more Natural Gas than expected this causes problems. I worked in an industry that was a large consumer of Natural Gas- huge paint ovens- arrays of large booths for painting that must maintain 70 degrees and 75% humidity. During a particularly bad winter on a bitterly cold week our industry was ordered to shutdown so the residential gas supply wouldn't be severely affected. They were having trouble getting enough Natural Gas to the Residential customers for the demands the severe weather required.

    A second heat system like a high efficiency Heat Pump can be a good back up in those times as well as insurance if natural gas prices spike. If the Natural Gas prices rise enough where a High Efficiency Heat Pump is cheaper it is a relatively easy to "lockout" the gas furnace and use only electricity or visa versa based on utility prices. It gives you flexibility.

    If you don't have experience with a new style High Efficiency Heat Pump you might be surprised- I have measured air duct register exit air temperatures of 110 degrees with our heat pump.
     
  14. TinyTim

    TinyTim Active Member

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    Heat pumps can cool down to 20F or even below. Their efficiency drops significantly below 35F. It's not the temperature of a gas furnace. It's the blow torch dryness of the heat from a furnace. If a person didn't have both a gas furnace and a heat pump. They probably would not feel the difference. If it's below freezing outside, people probably do not care if it's a dry heat. They market heat pumps as a more comfortable heating environment which is true. I simply have the choice between gas heat and heat pump heat. I gauge the set point of the heat pump shutoff more on comfort vs. cost.
     
  15. Trollbait

    Trollbait It's a D&D thing

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    The Prius Prime heat pump can heat the cabin with outside temps down to 14F. It can do this because the compressor is sprayed cooled by refrigerant. While the first automotive heat pump to use this technology, it isn't new, and has been available to the home HVAC market for several years.

    There doesn't seem to be a rash of complaints of low heat pump efficiency in the Prime, nor a large population of owners turning the engine on at a temp above 14F just for cabin heat.
     
  16. sam spade 2

    sam spade 2 Senior Member

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    I don't remember EVER wanting my heat pump to COOL when the outside temp is 20F. :whistle:
    I suspect that you meant "heat". (y)
     
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