Geothermal heat comfort in a 50 year old home with limited insulation and ductwork?
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  1. #1
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    Oct 2004
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    Geothermal heat comfort in a 50 year old home with limited insulation and ductwork?

    I'm trying to decide whether to invest in geothermal or not, and the issue I think is comfort not price. I have done research, got 3 bids on closed loop (all similar priced, but won't quote numbers on this website). The proposed specs varied between bidders - 2.5 ton versus 3 ton versus 4 ton. The 4 ton proposal included a summary of Manual J with Elite software. But out of the 3 bids I received for geothermal, the contractor whom I believe has the most experience with retrofits said that I *might not* be as comfortable with geothermal heating, compared to how I have not had any problems with comfort in the past using my oil forced air furnace (that furnace was replaced in 2003). He said that he cannot guarantee the comfort level, and so must caveat his bid that I might need modifications - either ductwork or insulation. He is being honest and says he does not want to lead a customer to spend money if he doesn't think it is the best idea. Meanwhile, I tend to trust his judgement as he has done quite a few retrofits of homes that are better insulated and have better return air ducts, compared to my home. To be sure, I am going to call 3 references once he gives me the phone numbers of previous customers who have had his company do a geothermal retrofit.

    I live in S.E. PA near a small town where the heating degree days annually are roughly 5000 to 5600. Based on his measurements, he said my ductwork sizing is good for airflow for a 2.5 ton geothermal heating, and up to 3 tons max would be just fine. The house never had central air and A/C is not the issue here for me, just heating is where I am concerned about saving the cost of oil over the long haul. (I have run calculations on this and no matter if oil prices escalate relative to electric slowly or rapidly, I will still save money eventually if I own the house 10 or more years, even including a 10 year home equity loan into the return on investment calculation).

    Given that the issue he said is comfort, I am reluctant to spend the large total investment cost if the net outcome might make the house very uncomfortable and then I end up spending 5 or 10 grand more on insulation or windows or both. Or worse yet, realizing I need more ductwork and in order to effectively utilize the increased airflow I would have to upsize the geothermal model to one with more tonnage.

    Last year I used 666 gallons of oil for a home living area of 1890 square foot (main floor plus upper floor two bedrooms) cape cod-style house. The basement is only used occasionally for exercise but is where the furnace is located. I really don't care if the heating of the basement is good enough since it isn't a daily living space. There is NO separate ductwork for heating the basement, just a small vent off the main trunk in the furnace room. I say this because including the basement in the Manual J would add 1200 sq ft to the area of the house.

    In the winter, my oil furnace which is probably 82% efficient and 105,000 BTUH, runs at most only 5 minutes, then shuts off for a while. My main floor thermostat is usually set at 69 deg overnight and 70-71 daytime. In the winter there are not any cool spots in the room near the walls, even though when I remodeled main floor bathroom I found NO insulation in the main floor walls. About 6 years ago I added heavy thermal drapes to all the main floor windows, which really made a difference in comfort because they are kept closed or partway open in the middle of winter. The second floor has a cape cod style sloped ceiling that has limited insulation, but with an oil-fired furnace the two ducts, one leading to each 13 x 13 size (plus alcoves) bedroom, was more than adequate for comfort. One bedroom is vertically above the basement furnace on the second floor, while other bedroom involves a 32 foot horizontal run of ductwork in the basement, then running upwards to the second floor.

    One contractor ran a Manual J based on including the basement, and the summary is as follows:
    "Total building supply CFM = 1837"
    "Sq Ft of Room area (including basement) = 3164"
    "CFM per sq ft = 0.581"
    "Sq Ft per ton = 723"
    "Total heating required with outside air = 77200 BTUH"
    "Total sensible gain = 40400 BTUH"
    "Main trunk size 12x28"
    "Room load summary:"
    "1st floor -- 875 sqft -- 36300 sens BTUH -- 342 htg nom CFM -- 4-8 run duct size -- 542 run duct vel -- 757 Air sys CFM"

    "1st floor addition -- 384 sqft -- 22500 sens BTUH -- 292 htg nom CFM -- 3-8 run duct size -- 480 run duct vel -- 503 Air sys CFM"

    "2nd floor -- 630 sqft -- 21300 sens BTUH -- 276 htg nom CFM -- 3-8 run duct size -- 522 run duct vel -- 546 Air sys CFM"

    "Basement -- 1270 sqft -- 7200 sens BTUH -- 93 htg nom CFM -- 1-4 run duct size -- 359 run duct vel -- 31 Air sys CFM"

    So I would think that these Manual J results should have allowed the second contractor to judge if my ductwork is undersized or if I needed more insulation, yet he did not suggest either, and meanwhile proposed a 4 ton system.

    The first contractor, who proposed a 3 ton system, said that I might need either larger ductwork or better insulation to be comfortable.

    Who is correct?

    Does anyone have experience with an older home (1950s to 1960s) that does not have ductwork or insulation equivalent to a new home, but was able to have adequate geothermal performance in the midatlantic area during the winter?

  2. #2
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    Oct 2004
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    37
    The other question I have is how do I go about figuring if limited modifications are needed, how to determine what modifications are cost effective?

    Regarding ductwork mods, should I ask the prospective bidder if he will do some type of airflow study, and give me a separate price for that? Or should he just be able to estimate based on his measurements of ducts, how much additional ductwork he advises and give me an installation price for that?

  3. #3
    Join Date
    Mar 2003
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    PA/DE area
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    I really like to see homes alittle new with GEO or tighter(some people want them I just state facts ,so if they are not happy they at least know before going into it).If the duct work in the home is size for 4 tons then your OK ,that means you should need to get rid and bring back around 1600 cfm(load says 1880 cfm) or if you have 6 inch feeds you would need 16 supply vents to get rid of that much air and bring back in a perfect world plus 20% more.You will be limited by SEER on your heat pump due to existing heater and if it is tall some coils will be tight.Also basement added in many be a mistake since it may cause unit to short cycle since it will be controled by thermostat in upper floor.Geo is pricey and a home of that size with an air source HP uses little oil at all.i have a link that a mircosoft guy made to let you cost it out.PECO gives you the break on air or geo HP.
    It's NOT the BRAND,it's the company that installs it!!!!!

  4. #4
    Join Date
    Aug 2008
    Location
    Cincinnati, oh
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    22
    heatpumpguru where is the link? is the software open for use or private?

  5. #5
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    Mar 2003
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    Send me an e-mail,he just made it himself and ran the numbers.it is not a website or anything
    It's NOT the BRAND,it's the company that installs it!!!!!

  6. #6
    Join Date
    Feb 2003
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    1,996

    If you're not lloking to reap the saving

    year round. It's gonna take you a very long time to get back the money spent on a geo
    system. I would look into insulation upgrades instead. The furnace is not that old
    and probably has at least another 10 year left in it. I'd assume you're heating water
    with an oil fired HW heater. How much of the 666 gals is for HW? Maybe you spend only 500 gal on heating. Not really much. I don't think a geo system is worth the expense. If I were you I would look into a solar water heating system and hydro-coil
    to heat the house in the sprint and fall. and give you hot water all summer and part of the winter. A duel fuel system is the best compromise. When the furnace does die, you get a boiler to drive the hydro-coil for warm air heat and drive an indirect for HW when the solar could not keep up. Get a regular split AC system for the 3 months of the
    year you need it.

  7. #7
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    Mar 2003
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    PA/DE area
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    In our area people use less then ONE tank of oil a year with the heat pump and they turn it to the oil around 35 degrees.If you look at the load with the a/c of 4 tons it will only cover the load to the same point or close to where the GEO does.It says you need 77k for heat and the GEOs around 5oK I assume,back up makes up the differnce.I do not know if you heater will drive 4 ton since most 105k have 3 ton drives.
    It's NOT the BRAND,it's the company that installs it!!!!!

  8. #8

    geo install

    I say go for the geo you need to make sure your duct system can handle the airflow no matter what type of system you go with. Most geo thermal units have de-superheater connections to help aid the waterheater in heating hot water for the home. My experience is mostly with waterfurnace brand equipment. Geo heat is a little warmer than your normal outdoor heatpump. It is eaiser to pull heat out of warm ground temps than cold outdoor air.Ther is not a unit on the market that can touch the eff% of a properly installed geo unit and that means cheaper operating cost to you.

  9. #9
    Join Date
    Oct 2004
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    37
    Quote Originally Posted by jhac1 View Post
    I say go for the geo you need to make sure your duct system can handle the airflow no matter what type of system you go with.
    Well, the problem is the contractor who recommends 4 ton did not actually measure and count my ducts and duct square areas. In addition he said that years ago he used to recommend all the ducting strictly by the book and found that many customers did not want to pay for the work, but most often those customers were still satisfied with performance.

    However, I'd like some opinions from experienced geothermal heating installers regarding whether the flow capacity is close enough for a 4 ton geothermal 2 stage furnace.

    All first floor is 6" diameter round horizontal duct runs, all second floor is 3" x 9" rectangular duct direct vertical runs down to main trunk in basement:

    First floor - Living room -- 2 ducts, 6" dia. - horizontal duct run distance direct to furnace is 20 ft for each duct.

    1st floor - dining room -- 2 ducts, 6" dia. - horiz. run dist. to furnace = 23' each, but only a short portion of this distance - 13' - until it joins to main trunk ductwork.

    1st floor - kitchen -- 1 duct, 6" - horiz. run dist. to furnace = 23', but only part of this distance - 13' - until joins to main trunk

    1st floor - bath -- 1 duct, 6" - horiz. run dist. to furnace = 29', but only 13' until joins to main trunk

    1st floor - bedroom #1 -- 1 duct, 6" - horiz. run dist to furnace = 39', but only 13' until joins to main trunk

    1st floor - bedroom #2 -- 2 ducts, 6" - run dist to furnace 38' each, but only 13' until joins to main trunk

    2nd floor - bedroom #3 -- 1 duct, 3"x9" rectangular vertical duct, 8' vertical dist. down to basement main trunk, then 41 ft. to furnace

    2nd floor - bedroom #4 -- 1 duct, 3"x9" rectangular vertical duct, 8' vertical distance direct to furnace

    Also, there is one heating vent in the basement on the furnace main trunk.

    Most geo thermal units have de-superheater connections to help aid the waterheater in heating hot water for the home.
    My water quality really sucks. PH 5. I've converted to all plastic source and drain pipes. Because the superheater would have a tank that tries to heat my well water, the problem is 3 year lifecycle of tank, even quality glass-lined water heaters. So I don't want to be replacing these really expensive superheater components, since they are much higher cost than my typical 300$ electric water heater. Long term maintenance cost would be worse than the hot water electric heat savings.

    My experience is mostly with waterfurnace brand equipment.
    From what I've read waterfurnace and climatemaster are pretty similar in quality. However, one installer told me that he can get stock parts MUCH quicker from local dealers for Climatemaster, but he has had trouble with delays from Waterfurnace.

  10. #10
    Join Date
    Mar 2003
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    We sell Carrier and they do not really stock the GEO parts
    It's NOT the BRAND,it's the company that installs it!!!!!

  11. #11
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    Mar 2003
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    PA/DE area
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    What is the style of home?colonial, cape cod,split level?
    It's NOT the BRAND,it's the company that installs it!!!!!

  12. #12
    Join Date
    Oct 2004
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    37
    Quote Originally Posted by heatpumpguru View Post
    What is the style of home?colonial, cape cod,split level?
    See first post: Small-medium cape with 26x16 addition, open air to dining room and kitchen. 1800 sq. ft. first floor plus second floor, 1200 basement.

  13. #13
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    Mar 2003
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    I tend to size around a 1/2 to smaller on the Capes to get run times due to large roof area and thermostat being on the first floor and it is easy to cool. Returns to the upstairs are key,if you do not have enough you may have to stick window units up there.That is really not the goal of a PRO.
    It's NOT the BRAND,it's the company that installs it!!!!!

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