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  1. #1
    Join Date
    Oct 2007
    Location
    KY
    Posts
    59

    How can I get a Systen like this?

    I have a 60 year old 1 1/2 story 1800 sf house with basement. Location is northern Kentucky. Little insulation and original windows with storms. Heat is a 150K gas Sunbeam furnace. Air conditioning is with a 3Tn Sears unit. I've had a furnace man look at it and am told that the ducts are pretty adequate for what I've got installed. I'm a good enough engineer to know that the main ductwork is not undersized that it will restrict airflow - maybe not correct airflow. Evidently the ductwork was replaced when the A/C was installed 30 yrs ago. There are some baffels in the ducts. Both the furnace and the gas water heater vent up the chimney and I would like to keep that arrangement. I don't want a "booger" on the side of my house. There are only three ducts to the upper level and the stairway is the return. Maybe some sort of fan with extra power to the second floor when the A/C is running? I've heard many noise storys about that and need suggestions.

    I've gathered from a lot of reading here that I do want to get some form of dual heat - Heat Pump and gas furnace. Makes a lot of sense to me, even though I make most of my money as a natural gas producer.

    Now, as I conceptualize what I want, I think I would want a system set up in somewhat this configuration:
    Air Filter
    Heat Pump Heat Exchanger / Air Conditioner
    Blower / Fan
    Furnace with plenum to add heat.

    I'd like to get something in the 80% gas range so that I don't have to put that booggr on the side of the house. I'm not too concerned about absolute best efficiency. I do want to be able to enjoy the immediate effects of calling for gas heat and getting it. What I have now is not very efficient, but it sure feels good when I want it to make heat, or cooling.

    My thoughts on that configuration of the elements are that I want to have the Heat Pump working as long as the Outside Air Temp is greater than XXX. It will add heat to the stream, maybe not enough. With a downstream furnace, controlled by some exit temp reading telling the furncce to operate, I can still get very warm air from the vents. If the Outside Air Temp falls below XX, the heat Pump will not be in the game and the modulating furnace will carry the full load. The thermostat should allow the homeowner to set that XX number for the Heat Pump shutoff. Probably in the 20F range that it will not be energy efficient to operate with .07 kwh costs here in KY. But I don't want to have an "One or Other" system.

    I sure would like to have a few advice comments on what I need. Perhaps what I want is not within the normal factory options. However, if it is, I'm sure the knowledgeable people here will know how to configure it.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    With that set up you will rust out the furnace heat exchanger.
    When the A/C runs in the summer, it will cause condesation in the furnace.
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  3. #3
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Holy cow, that furnace you got there sure is oversized for KY!

    I agree with beenthere. It's not going to work out.

    Coil has to be after the heat exchanger.

  4. #4
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,559
    A properly designed conventional system will provide you with a very comfortable home. Anything like this would be along more of a commercial application with individual zone heaters, dampers and thermostats to add heat to a zone if the air wasn't the correct temperature entering the zone. It would have to be hooked up to a centralized computer system and would be very cost prohibitive. I would find a good contractor in your area and let him design a system for you. Putting the furnace after the coil is a very bad idea, even if you find somebody to do it (and they are out there) don't do it.

  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Sounds like you've got several issues. It also sounds like your existing furnace is oversized but if the duct system is sized for a 3-ton AC system, I'd suspect the temperature rise on your furnace is astronomical and the unit is likely riding on the high limit when it runs. Based on those observations, I first and foremost recommend that a full load analysis be done on the home. Get a company in there that does Manual 'J' load analysis and once the appropriate sized of equipment are established, you can start on the 'wants'. You don't need to vent a 90+ furnace out the sidewall of the home. Most, if not all, have the capacity to vent through the roof.

    Your options are many. gas warm air w/AC/HP attached, gas boiler w/hydro-air heating/cooling, ductless mini-splits to do the 2nd floor that's less than comfortable, etc. You've got a little knowledge but based on what you wrote, the old cliche, "a little knowlege is a dangerous thing" you're headed down that road without solid professional advice. So keep your questions on the table and get a good company in there to help you design something that will meet all your wishes and needs.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Join Date
    Feb 2003
    Posts
    1,996
    As said, the chimney could be used as a chase for PVC venting, but then the WH would need to be PVC vented also. Hydro air would a good solution. Mod/con gas boiler to heat an indirect WH and hot water coil for the air handler for heat to supliment a heat pump. Another high end solution is a residential chiller. They have 3 ton units that could
    heat and cool, probably still need a boiler to suppliment and make HW. Nice thing about a chiller: an additional fan coil could be run up to the 1/2 story to heat and cool with just PEX piping. The ductless mini-split is another cheaper option.

  7. #7
    Join Date
    Oct 2007
    Location
    KY
    Posts
    59
    Quote Originally Posted by skippedover View Post
    Sounds like you've got several issues. It also sounds like your existing furnace is oversized but if the duct system is sized for a 3-ton AC system, I'd suspect the temperature rise on your furnace is astronomical and the unit is likely riding on the high limit when it runs. Based on those observations, I first and foremost recommend that a full load analysis be done on the home. Get a company in there that does Manual 'J' load analysis and once the appropriate sized of equipment are established, you can start on the 'wants'. You don't need to vent a 90+ furnace out the sidewall of the home. Most, if not all, have the capacity to vent through the roof.

    Your options are many. gas warm air w/AC/HP attached, gas boiler w/hydro-air heating/cooling, ductless mini-splits to do the 2nd floor that's less than comfortable, etc. You've got a little knowledge but based on what you wrote, the old cliche, "a little knowlege is a dangerous thing" you're headed down that road without solid professional advice. So keep your questions on the table and get a good company in there to help you design something that will meet all your wishes and needs.
    I've been down that "Dangerous Knowledge" path before on some other projects so I understand the advice. However, when I got finished with those projects I had acquired an education, though costly. In this case, I don't expect to be doing a HVAC project again so I don't want to get (or pay for) that sort of education on this project. I'll take the advice and try to keep it in mind.

    I do believe that I want to go the gas warm air with HP attached. Possibly a little more conventional for the area and likely to get better service down the road it there are any problems.

    Quote Originally Posted by beenthere
    With that set up you will rust out the furnace heat exchanger.
    When the A/C runs in the summer, it will cause condesation in the furnace.
    Thanks for pointing that out to me. However, I don't really understand why the AC coil I have now (located after the furnace, in the plenum) has not created that problem in the current setup during the summer cooling season. It does make sense that it would create that problem, except that it has not. Sure, I get condensation from the AC but it drains out and I've not found evidence of rusting from the moisture that is certainly remaining in the air. Everything in the current setup is over 35 yrs. old - that is how long I've owned the house. Maybe the new systems are so much tighter that the slightly more moist air will be more of a problem?

    As to the vent through the roof - The one contractor whom I asked about a system told me that I would have to run a liner pipe of some sort inside the chimney pipe, if I did not go with the vent out the side of the house. He seemed to not want to do that as he thought it could lead to troubles on the install. Something to do with a condensation issue in the chimney related to the more efficient furnaces. I would have thought the gas water heater vent air would take care of the condensation. I guess not.

    Anyway, I sure like the idea of the gas modulating furnace with the many incremental increases in output. And I've learned here the advantages of the variable speed blower that will help control the humidity in the summer. getting the right equipment speced and installed is the real puzzle.

    Thanks to all of you for the many knowledgeable posts that I've found here. Any direct suggestions for applications on my project will be appreciated.
    Last edited by aaCharley; 11-03-2007 at 01:03 PM. Reason: Correct some spelling

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    The A/C coil located after the furnace isn't cooling the furnace heat exchnger, so it doesn't condensate inside the HX.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Sep 2002
    Posts
    12,482

    You can do what you first detailed -

    IF - you used a 90+% furnace with condensate drains on both heat exchangers AND with both heat exchangers made from all stainless steel.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  10. #10
    Join Date
    Oct 2007
    Location
    KY
    Posts
    59
    Mikey and beenthere,

    Thank you both for the explanations.

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