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  1. #1
    Join Date
    Apr 2003
    Posts
    43
    My gas bill is getting more and more outragous. I used 120 therms last month and it cost $149.00 (only $5 was the base monthly fee), so $144 went to buy the gas. That is about $1.20 per therm. My electric rate is .06 cents per KWH. I live in east Tennessee in a 3200 sq. ft. 2 story home which is 5 years old. Well insulated brick home. I am debating on replacing the units with heat pumps as I am told theat gas will only go up, up, up going forward. As I stand now, would it be cost effective to replace my five year old gas furnaces with heat pumps? Thank you.

  2. #2
    Join Date
    Apr 2003
    Posts
    43
    Also, I would plan on replacing the water heater with an electric one.

  3. #3
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,973
    I would strongly suggest you look into a "dual-fuel" system. This utilizes a combination of heat pump and fossil fuel, in your case natural gas. I am just up the road from you in Ohio Valley, and I have lived in heat pump, natural gas, and now dual-homes, and without a doubt this is the best arrangement. It allows the heat pump to satisfy the heating requirement during those temps when it is most efficient (more than gas) and then lets the gas kick in when it is most efficient (more than electric) without any sacrifice in comfort (which was a real important consideration for me) If you were going to be in the house for any appreciable length of time, I would suggest a high efficiency heat pump 16 seer+ with a high efficiency (90+ afue) gas furnace. Put on a good quality filtration and humidification for overall good indoor air quality. I have top of the line Bryant Evolution system in my home (just like Carrier Infinity) and am very pleased with it. Dual-fuel is becoming much more common place where years ago it was something of an oddity.

  4. #4
    Join Date
    Jul 2004
    Posts
    253
    Originally posted by jrcase
    My gas bill is getting more and more outragous. I used 120 therms last month and it cost $149.00 (only $5 was the base monthly fee), so $144 went to buy the gas. That is about $1.20 per therm. My electric rate is .06 cents per KWH. I live in east Tennessee in a 3200 sq. ft. 2 story home which is 5 years old. Well insulated brick home. I am debating on replacing the units with heat pumps as I am told theat gas will only go up, up, up going forward. As I stand now, would it be cost effective to replace my five year old gas furnaces with heat pumps? Thank you.
    In order to answer this question you need to know how long you plan on staying in the house. Assuming you have an 80% efficiency gas furnace then you are getting about 67K BTUs per dollar. A heatpump will give you about 170K BTUs per dollar assuming a COP of 3 ( this varies by outside temperature so this is just a first order estimate ). For arguments sake lets say the heatpump reduces your heating bill by 1/2. Figure out your total heating bill and that is how much money you will save per year. Multiply that by the number of years you think you will be in the house and apply some approximation as to how much you think gas price increases will exceed electric increases and compare that to the cost of putting in a heatpump. Dont forget to compute the future value of the money you would spend on putting in the heatpump.

  5. #5
    Join Date
    Jun 2004
    Posts
    146
    Originally posted by irishmist
    I would strongly suggest you look into a "dual-fuel" system. This utilizes a combination of heat pump and fossil fuel, in your case natural gas. I am just up the road from you in Ohio Valley, and I have lived in heat pump, natural gas, and now dual-homes, and without a doubt this is the best arrangement. It allows the heat pump to satisfy the heating requirement during those temps when it is most efficient (more than gas) and then lets the gas kick in when it is most efficient (more than electric) without any sacrifice in comfort (which was a real important consideration for me)
    I would differ with the "without a doubt" part. With his gas rate of $1.20/therm, even a high (90%) efficiency gas furnace only produces 75K BTU's per dollar.

    The heat pump would only need a COP of 1.32 to equal efficiency of the high efficiency gas furnace. And heat pumps can do much better than that. So there's never really a point where gas is more efficient (not in his climate). From an economic point of view, a heat pump/resistance backup combination would be best.

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    I'm not well practiced at running energy savings numbers, so feel free to correct me if I goof.

    A typical heat pump might have a COP of around 3. At 80% efficient your furnace delivers 80,000 BTUs for $1.20. In the best case scenario the heat pump would deliver that for $.47. HOWEVER, my understanding is that the COP of 3 is under a best case scenario. As the temp drops, so does the COP. And of course, the electric back up heat (which kicks in way too often in most homes) has a COP of 1. AND, most heat pumps don't have a COP anywhere near 3 even in the most optimal weather conditions because most homes have moderately to severely undersized ducts. AND, if you have a tiered electric rate then your increased usage may bump some or a lot of your electricity to a tier higher than 6 cents per KWH.

    So what's the real number? It's anyone's guess. But hypothetically let's say that the real number turns out to be 70 cents per 80,000 BTUs. So you save 42%. If total gas usage for the year is $900, then you'll save $378. That's not a bad thing. But the cost of two brand new heat pumps systems (air handlers, heat pumps, linesets, etc.) might have a 20 year payback. Some may disagree with my calcs, but they're probably close.

    Whatever you do, don't let anyone sucker you with the heating degree days routine. That way of calculating energy savings gave me a number twice as big as the reality for my own home. The only real way to calculate savings is to use your past usage history combined with real world factors like the effect of weather on COP, duct losses, user behavior patterns (for example: the new heater is perceived as cheaper so the occupant uses it more and negates the savings), etc.

    I would add that most homes that are supposedly well insulated are in reality not. They have good insulation on paper. But in practice most homes have had their insulation installed very poorly. Get a energy consultant to run a blower door test with an infrared camera and you might be shocked at what you saw.

  7. #7
    Join Date
    Oct 2003
    Location
    34.8n 102.4w
    Posts
    3,244

    Big home

    In a different aspect, it only cost a nickel a square foot a month (and less if you consider water heating usage )....How much do you expect to pay for comfort?
    Life goes on long after the thrill of living is gone.

  8. #8
    Join Date
    Jul 2004
    Posts
    253
    Originally posted by jrcase
    My gas bill is getting more and more outragous. I used 120 therms last month and it cost $149.00 (only $5 was the base monthly fee), so $144 went to buy the gas. That is about $1.20 per therm. My electric rate is .06 cents per KWH. I live in east Tennessee in a 3200 sq. ft. 2 story home which is 5 years old. Well insulated brick home. I am debating on replacing the units with heat pumps as I am told theat gas will only go up, up, up going forward. As I stand now, would it be cost effective to replace my five year old gas furnaces with heat pumps? Thank you.
    A lot of your decision should come down to where do you think gas rates are headed. If you think they will track with oil rates and triple in the next 5-10 years ( I am pulling a number out of thin air ) then switching out to a heatpump may make a lot of sense. Your electic rates are cheap ( 30% less than mine in GA ). Electricity in this country is mostly generated from coal and nuclear ( altough your state probably has a pretty high hydroelectric component - havent looked ) which somewhat isolates electric costs from oil costs. As someone else suggested, I would take a serious look at your insulation and try to improve that and then reevaluate your gas costs in terms of whether switching out to a heatpump makes economic sense given the number of years you think you will be in the house.

  9. #9
    Join Date
    Oct 2004
    Posts
    100
    Dawg
    I agree with you. A cost of $149 to heat 3200 sqft house and water, in January. What do you expect to save? Here in North Carolina, I see $400 gas bills in houses half the size of yours.

  10. #10
    Join Date
    Apr 2004
    Posts
    7,680
    You need to look at several factors. Grab hold of a spec sheet and follow along. Heat pumps are rated in heat at two points. 47 degrees ambient and again at 17 degrees ambient. These are real numbers and real conditions. I'm going to review some basic fundimentals so take no offence, it just helps me lead to my point.

    At 47 degrees you will most likely see the capacity of the system near the nominal rating of the unit (a 3ton hp might offer about 36,000 btuh's at a COP of, I dunno lets say 3.3 COP.) Im making numbers up so bear with me.

    At 17 Degrees the same system may have a reduced capacity of say 23,000 btuhs with a reduced COP of say 2.4.

    Reviewing what we all know already the COP is the efficiency of the heat over straight electric resistance heat which is 100% efficient. The COP of 3.3 is 330% efficient. or can produce the same mount of heat as electric at less than 1/3 the cost. Agreed?

    Now we look at the heat loss of the structure and the 47/17 ratings and determine the point at which the HP requires absolutely no electric heat (when the heat loss of the structure intersects the capacity of the system), this is the balnce point. As long as the temperature is above the balance point lets say 28 degrees (again just a hypothetical number) we are heating the home at a point far more efficient than straight electric. (bwtween 3.3 and 2.3 times).

    Eventually the balance point is breached and we now do not have enough capacity to heat the home on hp alone. Now, if we turned off the HP and switch to straight electric, we would indeed have fairly costly operation. But we dont, we bring on auxiliary heat which makes up the percentage of heat we lack with the HP. Now depending on where you live you need to look at the time spent below the balance point, how far below and for how long. Generally, especially in TN, you dont last for long below the blance point for long. Yeah in a cold snap you may for a few days but in general your winter average temps are above that point. You do need to enter real numbers to get your final cost analasys. Maybe someone her can throw a real set of calcs up from a recent job quote. Granted you have to defrost but thats a slight reduction not major.

    HP's in almost all cases are less costly to operate than gas and at $.06 per KW you would never be able to touch that with gas when it comes down to cost. A fossil fuel kit maintains the efficiency of the HP with the perception that gas is more comfortable (that can be argued if thje distribution system is proper). This is the set up I use with the understanding that I pay a little more than if I had a straight HP.

    As Irsh said, consider an add-on HP (dual fuel)if your furnaces are in great shape.

    [Edited by docholiday on 02-13-2005 at 11:11 AM]

  11. #11
    When you compare gas to electric heat ( in any form including heat pumps ) first realize that you are not comparing apples to apples, there would need to be a cosiderable cost savings I think in the 25% range to even start to consider electric as an alternative to gas heat.

    If you want to know the cheapest way to heat your house it is with the condenser of an ice machine, at least in my area.

  12. #12
    Join Date
    Apr 2004
    Posts
    7,680
    Work with me here eddy... Why would you have to save 25% to make it better? Thats darn right silly. I suspect you never have been comfortable working on them and if that is so, then maybe its best you dont recommend them because that are unfamiliar territory.

    His simple question was which would cost less, a dollar is a dollar and that is indeed apples to apples. There a some real clowns out there that think its going to be 0 degrees for months on end, it just isnt true here in the lower 48. For the 3 or 4 days it is that cold you pay more but for the rest of the year you pay less, much less.

    He's looking for an alternative source of heat, why not use an add on HP? Keep from burning any gas until it's really needed.

    Maybe Im missing smething here but isnt a heat pump the condenser side of an ice machine? (heat with the condenser, the evaporator is outside and makes ice).

    Yes mechanical movement of heat will cost less than the actual production of heat.


  13. #13
    Join Date
    Oct 2003
    Location
    34.8n 102.4w
    Posts
    3,244

    DOC

    Yes, I think you are correct in the fact that a heatpump will produce BTU's at a discount rate. I understood jrcase to say his unit was only 5 years old and that led me to think... well how much do you want to spend on comfort. IF his unit was out , it would be a no brainer. But I would have a hard time justifing the cost NOW... But, it is his castle also.. and his cash.
    Life goes on long after the thrill of living is gone.

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