update furnance / AC with better efficiency heat pump?

Discussion in 'HVAC Heating & Cooling' started by geo88, Aug 25, 2013.

  1. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    Howdy,
    Just joined the sight and looking for viewpoints. Especially in conservation ($$ and fossil fuels).

    I live in an older home, 1997, in NE Kansas. I have central heating and cooling. Propane for heat and air conditioner for cooling. The furnace is a RUUD 90 Plus and the AC is a RUUD 5 ton, model unknown. We have lived here 4 years. We have insulated appropriately and are in the process of replacing windows with higher efficiency. We believe we have done the right things in conservation areas, ducts sealed and insulated, etc. The energy bills have reflected our efforts.

    The primary question is in the area of central air and cooling. Would we be better off in replacing our AC with a air source heat pump and just keeping the propane system on line as a necessary backup? Should we consider replacing the whole system? Just replace the AC? Perhaps wait for failure then replace, since these are old units?

    My present reading suggests that a geothermal system is very overpriced with the pay back times questionable even with the tax incentives.

    Please give me your input and let me know if I am asking the right questions.

    geo88 in NE Kansas
  2. Dana

    Dana In the trades

    Messages:
    2,923
    Location:
    01609
    Until you have priced it out, you have no idea whether the economics of ground source heat pumps (GSHP) are going to work for you. But the first and most-critical aspect is to find a contractor who is actually COMPETENT to design & install them, since a hack contractor can bring even the best equipment to it's knees efficiency and even capacity-wise. In my neighborhood GSHP averages about $9K/ton, and delivers an seasonal heating-season average whole-system (all pumping & air handler power accounted for) coefficient of performance (COP) between 3 & 4 (even though best-case implemetations might be bumping on 5.) The high local average cost is likely due to a number of factors- little competition/demand, and the need to drill through granite rather than trenching slinkys into swamp dirt for the the earth heat exchange. In other parts of the US $5-6K/ton is the norm for small to mid-sized systems. Every system is unique, and the ultimate efficiency & cost falls in to the hands of the system designers, which makes it hard to do budgetary financial analyses around. (A $14K 2-ton system that runs a COP of 4 would be a pretty good deal compared to a $28K 3-ton system delivering a seasonal COP of 3.)

    Air source heat pumps tend to simpler to specify and design around, but they're not issue-free either. A poor implementation can bring the net efficiency down to a seasonal heating-season COP of 1.5 or less. Ducted heat pumps that are right-sized for the heating load, on systems with well insulated well sealed ducts might come in a COP of 2 or slightly better in an NE Kansas climate, but well thought out ductless heat pumps (mini-splits/multi-splits) can average a COP of 3-3.5 during the heating season in that climate, and blow away any ducted split-system on cooling efficiency.

    If you're replacing your AC anyway, the up-charge for going with a heat pump isn't huge, and with the price volatility and sometimes high expense of propane it can be worth getting off it if you can.

    All worthwhile HVAC systems start with a room by room heating & cooling load calculation. Odds are pretty good that your existing AC system is ridiculously oversized for the load (particularly after you've insulated and air-sealed both the house and the ducts), likely sized with the old-schooler's " a ton for every 500 square feet of living space" kind of rule, with some extra "just to be sure". Many factors make rules of thumb like that impossible to use well (shading factors, amount and type of west facing window area, ducts in the attic above the attic insulation, etc.) but most homes with reasonable insulation levels come in at about a ton/1000' (or more.)

    With a ZIP code, and propane billing with exact fill-up dates and the existing furnace's nameplate efficiency numbers it's possible to calculate an upper bound on the heat load, but not a cooling load. The room-by-room heat load & cooling load numbers will still be important for figuring out how to proceed.

    If it's a fairly open floor plan a single properly sized heating/cooling mini-split can take a HUGE slice off the heating & cooling bills for comparatively low money. A ton of ductless still puts out ~15,000 BTU/hr at your likely low single-digits F 99% outside design temp, and many 2500-3000' homes of the 1990s could be heated almost entirely with 2-3 heads and 2-2.5 tons of ductless heat pump at near-geothermal efficiency for well under $10K in (unsubsidized) installed cost.

    BTW: Since when is 1997 considered "an older home"? My 1923 vintage house is barely middle-aged by local standards, and I've dealt with plenty of pre-1850 homes, as well as a few pre-1800. I'll bet your house was even built with sealed double-panes, and insulation, but probably little or no foundation insulation, and ducts in the attic(?).
  3. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,227
    Location:
    Maine
    Unless our equipment is having issues there is not enough energy savings to justify the expense of replacing it. The Ruud 90+ series are pretty good pieces of equipment and I suspect the AC was matched to the furnace and its about as efficient as AC units gets.
  4. Dana

    Dana In the trades

    Messages:
    2,923
    Location:
    01609
    At $3-4 propane there can be a financial rationale for replacing a condensing propane furnace with a high efficiency heat pump. At $2 propane not so much. A 5 ton AC unit would usually be ridiculously oversized for an average sized home, but the consequences would be more on comfort than efficiency. Most fossil-fired furnaces are also ridiculously oversized for the actual loads too, and again, the consequence would be more a hit in comfort than efficiency.

    If the equipment is all 16 years old it probably has considerable life left in it, but it's always better to at least consider the replacement options before it becomes unreliable, and have a plan going forward. Knowing the actual loads to be able to right-size the replacement equipment would be step one, and CRITICAL if the replacement is something as expensive as a ground source heat pump.
  5. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    Dana,

    Thanks for your thoughts and input.

    I have had two bids for GSHP installation in 2010. Did not want to make any decision until I insulated better and tried to tighten the house down a lot more. The two bids were from a Waterfurnace and a Geocomfort installers. By history they have competency in this area, but how do you really know?

    The Waterfurnace bid was for an open loop, with well water, replacement of RUUD propane heat with Coleman high efficiency gas furnace (propane) and I believe included the air heat pump. The installer preferred horizontal loops since I am on 25 acres. His brother in law does the digging. Otherwise he contracts out the well drilling if we were to go that route. The payback on the GSHP sounds a little ambitious. His letter follows:

    "Attached is the info for the geothermal system for your house. The geolink will show you the cost of operation for the geothermal system vs a propane furnace and air conditioner. The system we have sized based on the heat loads is a 5 ton system with using well water for the loop. The Envision System has a dual capacity compressor, R410A refrigerant, desuperheater coax for heating domestic hot water. This system has a 10/5 year warranty- 10 years parts and labor on everything inside the heat pump box (compressor, air coil, blower motor) and 5 years on the t-stat, and well controlls. The geothermal system will heat all year for $1238.00, cool for $336.00, and hot water for $142.00 for a yearly total of $1716.00. This system will be installed for $18,224.00 and you will get a tax credit of $5467.20 for this system. The gas furnace is a coleman system with a 5 year warranty. It will heat for $3454.00, cool for $450.00 and hot watr for $527. for a yearly total of $4431. This system will be installed for $9375.59 and you will get a $1500 tax credit for this. The payback on the investment for the geothermal vs the gas furance and a/c is 1.7 years. You will be saving $226.00 per month with the geothermal system."

    The other bid follows, note the backup heat here is electric, which is not a good idea to me, the loop is vertical wells, is the well drilling in the bid or separate, not sure:

    "For your reference, the existing Ruud furnace has a 5 “ton” blower on it and is 16 years old as we suspected. The geothermal system will operate with one set of equipment. Our bid is to have a 5 “ton” system installed. We have chosen a two-stage compressor and variable speed fan motor to optimize energy efficiency during more moderate outdoor conditions. The backup heat is 20 kilowatts. The groundwork and drilling is quoted for 5 vertical wells.

    The installation will require a minimal amount of ductwork changes. Electrical work will require running new wire back to the breaker panel to wire the emergency “strip” heaters. The electrical that ran the outdoor compressor will now be used to run the compressor that sits in the basement.

    All proposals include labor, material, and sales tax. Once installed, all electrical is tested and refrigerant pressures are checked to manufacturer specifications. The equipment is tested thru the start-up sequence and operation to confirm proper operation. All equipment quoted uses the new refrigerant R-410a, commonly referred to as “Puron”. We made this decision several years ago considering the 2010 deadline when manufacturers will no longer be able to produce equipment that uses R-22, or Freon. Finally, this includes a return visit in late spring/ early summer to confirm proper loop pressures. This should continue to be actively checked several times a year for the first few years of operation.

    This quote is to furnish and install a GeoComfort Compass 5 ton, 2-stage ground source heat pump with variable speed blower, 20kW electric back-up heat, 3H/2C digital multi-stage thermostat, sheet metal ductwork. This equipment will be piped to the existing water heater or new buffer tank for de-superheater operation.

    Our installed price is $22,347.00 with a ten year labor warranty and manufacturer’s warranty on equipment. This price includes sales tax. This quote is good thru the end of April 2010.

    Once installed, invoiced and paid, you will receive an AHRI (Air Conditioning, Heating, Refrigeration Institute) certificate to authenticate performance information. You will keep this for tax credit purposes. "

    Well, for us, 1997 is an older home, not old home, or really old house. Not sure the defining dates!!! There were double panes, but leaky, an limited attic insulation. We have a full unfinished basement. It is not insulated and neither is the basement ceiling. While I insulated the branching ducts, I did not insulate the big ducts in the basement as that gives off some passive heating. I may be better off insulating the basement or ceiling. Attic is now about 60R value, ducts covered well, and sealed.

    I do like the concept of ductless heat pumps, kinda like the concept of room heating in the old house of yesteryear. Will have to consider that as well.
  6. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    You are probably right TS, I am kinda fed up with "Feral" gas attitude.
    geo88
  7. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    Dana,

    Currently "Feral" Gas is $2.15 per gallon. I do think the ductless air source heat pumps would be the way to go!
    geo88
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    5T is the equivalent of around 60K BTU. Depending on the house, you actual load may be closer to half that. You really need to assess your actual needs - just plopping in the same-sized equipment is just bad form. Rarely was it sized properly at the time of installation.
  9. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,227
    Location:
    Maine
    At 22 large you will be dead or the equipment will be long before you ever realize a cent of payback.
  10. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    JD,

    Exactly how is a "load" determined/calculated? Not too many gory details please.
    geo88
  11. geo88

    geo88 New Member

    Messages:
    6
    Location:
    NE Kansas
    TS, note the WF bid said payback was in 1.7 years. I am 64 so hopefully I won't be dead by then.....but I am skeptical about the payback time.
    geo88
  12. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,227
    Location:
    Maine
    He lied. Get that part in writing. Think about that. You are going to clear the 22 thousand cost in 1.7 years of fuel savings? If so you must have one really big and badly insulated house.

    Just take your annual fuel and energy cost and lets say it runs 1500 bucks now. Even if you cut that in half, which you won't, you would save 750 a year. Now divide 22 large by 750 that rounds out to 29 years which indeed if you make it to 93, I doubt you will be in shape to do much cheering besides which, in 29 years I sincerely hope technology is vastly improved.

    But hey, if you have a pocket full of money you want to get rid of I'll give you my address LOL. Seriously, I think whoever is quoting this is being less than honest and probably preying on the elderly. Not that 64 is elderly or I hope not because I'm pretty close to you but then again I tend not too spend much time looking at myself in the mirror which would probably confirm my fears. Did anyone see where my hair went?
    Last edited: Aug 28, 2013
  13. Dana

    Dana In the trades

    Messages:
    2,923
    Location:
    01609
    A 5 ton system is simply ridiculous for most houses. How big is this place?

    If the all-in cost (including dirt-work) pres-subsidy cost is $22K, that's literally half the cost per ton as what people are paying in my neighborhood, but almost certainly getting onto 2x oversized for the actual loads. A "typical" 2500' house built in the 1990s would have heating & cooling loads under 3 tons unless it has huge expanse of "sunset view" west facing window area boosting the cooling load to new stratopheric highs. Unisulated ducts in an attic above the attic insulation could add another ton, but even then... The tonnage of the compressor isn't exactly the same as the BTU/hr heat & cooling loads- it's rating can be either higher or lower than the loads on the house, with up/down on the compressor a function of the soil temp and the heat/cool distribution temps. But it's not a 2x multiplier EVER.

    Two stage heating is almost never really cost-effective with GSHP. If you size the system for a fairly aggressively calculated 90% heat load and use of resistance heating to cover the shortfall doesn't add up to much annually or even over decades, compared to the cost of an additional ton of GSHP.

    Heating loads are simper to calculate than cooling loads. If you can use a spreadsheet tool you can get pretty close using the classic I=B=R methods with some fudging at the end. If you know your wall construction type and insulation R values, (including foundation type & insulation ) I could spit out some U-factors for you to use.

    A U-factor is the heat loss per square foot of exterior area per degree-F difference across that assembly. For an outside temperature pick the 99% outside design temp for your area, then for an inside design temp use something between 68-72F. A typical outside design temp for KS is about +5F, so using an indoor temp of +70F would mean a difference of 65F.

    A U-factor for pretty-good 2x4 construction wall with wood siding would be about U0.08 BTU/degree-foot, crummy 1950s 2x4 with aluminum siding might perform as low as 0.1. For 2x6 with R19s it's about U-0.055-0.065. Say yours is wood-sided 2x4s with R13 insulation, and you measure up all of the outside wall area (less windows & doors) and it came up with 1600', the wall losses would be:

    0.08 x 1600' x 65F= 8320 BTU/hr

    You do a similar thing for the U-factors of the window area, attic area, exposed foundation area, etc, and add it all up. Then make some adjustments subtracgin for internal heat sources like 250BTU/hr per sleeping human, 150BTU/hr per refrigerator, 300 BTU/hr for the Tivo, etc. and add some fudge-factor for air leakage, and you have a pretty good handle on the heat load.

    If you know the manufacturer's U-factor for the windows, use those. Otherwise figure U0.6 for any clear-glass double-panes, U1.0 for single panes, and unless you have insulated doors, use 0.5 for the door area too. For an R30 batt insulated attic call it U0.045, for R38s call it U0.03. For uninsulated above-grade foundations (down to a foot below grade) call it U1.0.

    These aren't precision numbers, but they'll be close- close enough to tell you how insane 5-tons (60,000BTU/hr) of heating would be, unless this is 4000' of house with a lot of single-pane glass.

    If you know your wintertime propane use you can use the furnace to be the measuring instrument, but there are some inherent factors that would cause that to be on the high side of reality (eg: ducts in the attic rather than inside of conditioned space.)
  14. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,227
    Location:
    Maine
    He needs to add his electric cost to the gas cost too but its only going to verify what we are all saying.
  15. Dana

    Dana In the trades

    Messages:
    2,923
    Location:
    01609
    Residential retail electricity in KS is currently averaging 12 cents/kwh, delivered, according to EIA data.

    In a KS climate a ductless air source heat pump averaging a COP of 3 delivers a bit more than 10,000 BTU/kwh to the house, so at 12 cents you're talking a cost of a bit less than $12/MMBTU. A best-in-class modulating ducted version would probably come in at ~$18-20/MMBTU after duct losses to the unconditioned attic, addtional air infiltration, and air handler power.

    Electric resitance heating (cove heaters, baseboards) with 12 cent electricity is 3412 BTU/kwh or a cost of about $35/MMBTU.

    Propane has about 91,500 BTU/gallon, burned in a 95% efficiency burner assuming no duct losses or air-handler power you're looking at ~87,000 BTU/gallon of heat delivered to the house per gallon, or 11.5 gallons/MMBTU, which at $2/gallon costs $23/MMBTU. Realistically, with ducts above the insulation in the attic and with the air handler power you're really talking $28-30/MMBTU in operating costs- cheaper than resistance electricity, but not by a heluva lot.

    The price of propane is volatile, electricity is regulated, and in the midwestern wind-corridor well bounded in price. If propane hits $3-4 (like it has in recent history in New England) heat pumps become a no-brainer type of investment even in areas (like mine) where residential retail electricity prices is ~16 cents or more. But if propane stays at $2, even if you're burning only 1000 gallons a year it could better than a decade to pay off the cost of a new heat pump system. If the anticipated lifecycle of the existing system is coming to a close there's little point in waiting, but if it has a decade or more, it's a matter of divining the future costs of both electricity and propane from the tea-leaves, a notoriously difficult thing to predict.

    If you believe those slurping the frack water Kool-Aid propane prices could even fall (personally I'm not assuming that's very likely), and if you buy into the notion that the falling levelized cost & increasingly ubiquitous wind & solar are going to set the spot price of electricity within a decade, suppressing the retail price of electricity in KS for the next few decades (possible, maybe even likely IMHO, given how it has played out in IA & TX), the rational date when pulling the trigger on heat pump systems may be sooner than the remaining lifespan of the existing equipment. But assuming flat pricing on both there's no financial urgency for the swap out- it depends on your own personal discount rate in the net-present-value calculation. Most people's purchasing behavior on all things efficiency indicate a much higher discount rate than those used by utility companies for making investment decisions. YMMV.

    A really poor system implementation with uninsulated and leaky ducts in an attic in a very air-leaky house would likely have cost-effect air sealing & insulation remediation, independently of what's using the ducts.
Similar Threads: update furnance
Forum Title Date
HVAC Heating & Cooling keep haveing to hand start oil furnance Dec 11, 2009
HVAC Heating & Cooling Furnance Oct 19, 2008
HVAC Heating & Cooling Smelly furnance Feb 8, 2008

Share This Page