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  1. #1
    Join Date
    Jan 2006
    Posts
    25
    Hello, I am having a home built in OKcity,(2160 sq ft) and I am using foam insul in attic/walls. Possibly could put unit in garage, but attic seems easier? I was told that I need a 90%eff or higher condensing unit in the attic. My question is about one stage condensing units (var speed ok too)- which models would meet this requirement? Best quality/price assuming correct sizing and install? I was looking at Lennox G51 elite series, but open to any others...Is this a sound idea given insulation plan? Is neg air pressure a concern given the sealed attic space? I know, too many questions, but I am trying to be informed before investment is made...
    Thanks, Dave

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Thumbs up Furnace in garage

    Originally posted by señord

    home built in OKcity,(2160 sq ft)
    foam insul in attic/walls
    Possibly could put unit in garage, but attic seems easier?
    Lennox G51 elite series
    Is this a sound idea given insulation plan?
    Is neg air pressure a concern given the sealed attic space?
    Negative air pressure is a reality that must be addressed.

    http://www.airtightinsulation.com

    Suggest to use:
    Dual Fuel (heat pump + gas ) with
    furnace in the garage
    and hard duct ( metal or fiber board) extended plenum to near mid-point of residence and flexible ducts in the attic.

    http://www.lennox.com/products/overview.asp?model=HPX16

    Possibly a 4-ton may be the right 2-stage unit.
    Floor plans, insulation R-value, and window schedule/U-value & S.H.G.C. are required for one to size accurately.

    http://www.lennox.com/products/overview.asp?model=G51
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,451
    Keeping the air handler inside the insulated building cavity (sealed attic) has many advantages. Biggest is any air leakage of the airhandling system remains in the conditioned space. Pollutants from the garage should be isolated from the home. You need make-up air for health, operation of appliances, clothes drier, kitchen hool, bath fans etc. Make-up air should include air filtering and dehumidification in green grass climates. I am involved with a pioneer, +15 years, of the concept, Ultra-Aire ventilating dehumidifiers. This concept provides filtered, fresh air/<50%RH without operating the a/c or regardless the outside temperture. TB

  4. #4
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,744
    spend a little more go with lennox G61MPV

  5. #5
    Join Date
    Jan 2006
    Posts
    25
    50 bucks for man J might be a good idea. I am from
    calif. so I am not knowledgeable reg. heat pumps. Time for a little lesson "for" the teacher here. (Of course I will research it, too) anyway, always had cent h/ac in all 3 homes in the hot central valley. What humidity precautions are taken generally in S.W. OK city? We were there this last thanksgiving, (been to cancun twice) and the adjustment to humidity from our hot dry climate is nota problem. But for issues reg. home construction hvac needs, I can only call my cousin to ask what I should do...Thanks to those who posted previously... Dave

  6. #6
    Join Date
    Jan 2006
    Posts
    25

    heat pump efficiency

    I do recall reading that heat pumps are either one of or the most efficient of heating options. Is this increased performance worth any increase of price, if there is one?
    thanks again!

  7. #7
    Join Date
    Mar 2004
    Posts
    1,042
    Heat pump or dual fuel is my recommendation. Gas-only heat isn't going to be a good choice as far as operating cost goes. As I remember, winter electric rates are very cheap in your area (can you confirm?) so an all-electric heat pump would be the most economical to run.

    Lesson for the teacher: A heat pump is simply an air conditioner with a few extra controls that allow its operation to be reversed (in fact in the early days they were called reverse cycle air conditioners). A regular air conditioner doesn't "make" cold; it pushes heat from one area (inside) to another area (outside). A heat pump can do just the same, or when you ask it for heat instead, it pushes heat from outside to inside. This is very energy efficient and in most areas is very cheap to run. Just like an air conditioner does in the summer, a heat pump has to run a long time to do much good; in the coldest parts of the winter, it may run nonstop for days and days straight. Poorly set up heat pumps can produce heat that feels very lukewarm coming out of the vents, though, to the point of being drafty, so you have to be careful; it's very common that they aren't set up very well. Many people don't like heat pumps because they've only experienced setups that didn't produce good comfort.

    In most applications a heat pump can't move quite enough heat to totally do the job by itself in very cold weather, though, so you need a backup heat source for those times. An all-electric heat pump uses regular heating elements as its backup; they *add to* the output of the heat pump as needed to make sure you have enough heat. The heating elements are much more expensive to run, but since you only use them for a few hours here and there, and they're only covering the shortfall between how much heat you need and how much heat the heat pump is pushing into the house, it works out fine in mild to moderate climates. In the right climate and with decent electric rates, this setup is likely the cheapest up front (though not a huge difference) and among the cheapest to run, too. In a "dual fuel" setup, you use a gas (or oil or propane) furnace as your backup heat source. Those can't operate at the same time as the heat pump, though, so when the heat pump isn't enough heat to keep up by itself, the heat pump shuts off and the furnace takes over the whole job. This setup is a little more complicated and costs a little more up front, and in your case probably couldn't quite match the operating cost of an all-electric system, but it guarantees you nice hot heat when it gets cold outside.

    If you do end up with a furnace inside the building envelope, you will have to provide it with combustion air to keep from depressurizing the house. By far the simplest and best answer is to use a "2 pipe" condensing furnace; one pipe is the air intake, and one pipe is the exhaust. This is common and not expensive, but some folks get lazy and try to skip using the air intake pipe. Don't let them. Or with an all-electric heat pump, there is no need to deal with combustion air intakes or exhausts at all, because there is no combustion.

    The first and foremost concern for humidity control is to get the equipment sized correctly. The way to do that is with a Manual J calculation, either performed by a contractor or by yourself using the plans and some handy-dandy software. You can get a homeowner version of the HVAC-Calc software on this site (red tab above) for $50. Going by square footage alone is already a bad idea, and typically when you build a very efficient structure- like with foam insulation- you end up even more oversized than usual. This is a good application for an ERV (energy recovery ventilator) or ventilating dehumidifier, too, to allow for some fresh make-up air to exchange in this very tight house. Other good options for additional humidity control are using variable speed indoor equipment, especially with a dehumidistat or humidity-controlling thermostat.

  8. #8
    Join Date
    Jan 2006
    Posts
    25

    great info

    Thanks WYOUNGER. I checked up on rates in OKcity,and
    not to my amazement, the rates are LOWER than cent calif.
    I believe the heat pump may present savings, but I am
    still not convinced on significant vs. just a little. I feel that with the relatively smal size of home, and that we are home mostly evenings, weekends, holidays, and summer, I can not justify additional cost. I was planning to go with top of the line Lennox equip (G61mpv, and 21 SEER AC units) as a dealer said that the ballpark of increased cost was a bit lower than I had originally thought. Maybe I could price in the humidity control options and air cleaner by going with the elite (one level under signature) equip and still be very happy with utility costs.
    On the OGE website, I ran a quick home calc on hvac costs (although they did not provide a KWH or therm cost, and did not factor in beefed up insulation, or future price increase for elec rates) that my average monthly bill would run $100.00. I would be very pleased with that number, but I would be hard convinced that additional savings are significant to consider diff equip. This figure probably factors in 12 or 13 seer, and 80% furnace, too. (I have no data to assume otherwise, just a gut feeling that they are using an industry standard for their calc for "high energy efficient home" option in menu). Should I not consider equip upgrade given this data? Spend now or save in long haul always a toss-up, but I like to err on the side of super efficient...
    What humidity equip would you recommend for these Lennox systems if used?
    All comments welcome, my builder scheduled Feb. 2nd. for foundation to be poured. I still have time. The education on the heat pump was very helpful still...

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Re: great info

    Originally posted by señord
    I checked up on rates in OKcity,and
    not to my amazement, the rates are LOWER than cent calif.

    I believe the heat pump may present savings, but I am
    still not convinced on significant vs. just a little.

    I feel that with the relatively small size of home, and that we are home mostly evenings, weekends, holidays, and summer, I can not justify additional cost.

    I was planning to go with top of the line Lennox equip (G61mpv, and 21 SEER AC units) as a dealer said that the ballpark of increased cost was a bit lower than I had originally thought.

    Maybe I could price in the humidity control options and air cleaner by going with the elite (one level under signature) equip and still be very happy with utility costs.

    On the OGE website, I ran a quick home calc on hvac costs (although they did not provide a KWH or therm cost, and did not factor in beefed up insulation, or future price increase for elec rates) that my average monthly bill would run $100.00.

    This figure probably factors in 12 or 13 seer, and 80% furnace, too.

    Should I not consider equip upgrade given this data?

    Spend now or save in long haul always a toss-up, but I like to err on the side of super efficient...

    What humidity equip would you recommend for these Lennox systems if used?
    A/C will provide 45% R.H.
    NO NEED for additional humidity equipment other than
    Vision Pro 8000 or similar.

    High Efficiency ( > 15 SEER) Heat Pump
    likely cost less to install and significantly
    less (> 20% ?) to operate than
    subject gas furnace with A/C.

    You are most likely already
    paying MORE than nece$$ary
    based on life-cycle costs
    if you are buying a 21 SEER.

    Send plans via e-mail or mail.
    Provide gas and electric rates.

    Specific equipment selection,
    duct layout,
    and annual energy use
    can be provided.

    [Edited by dan sw fl on 02-01-2006 at 07:11 AM]
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #10
    Join Date
    Nov 2001
    Posts
    1,874
    most people up grade to better equipment cause they want to keep more of their own money, rather then give it to the gas co.

    You have the chance to install a H/P so that you will use less gas(a good thing), You could as stated above install a 15 seer H/P in exchange for the 21 seer a/c. You'll get more use from the H/P and the savings will pay you dividends for yrs to come.(a good thing)

    Go with VS drive indoors and your seer will increase by about 1 which means, More comfort, less humidity, lower utility bils, more money in your pocket,( all Good Things)

    Your area of the country,will still freeze in the winter, if you go in the attic, that could be a problem if it's not a well thought out install. With safties and heat tape.

    Going in the garage with the R/A above and the supplies in the floor will prevent freezes,
    Supplies in the ceiling and returns in the floor, will even help with dust, The dust will settle to the floor area, being picked up by the returns, and sent to the filter.
    If you try to fail, and succeed.
    Which have you done ?



  11. #11
    Join Date
    Mar 2004
    Posts
    1,042
    Originally posted by Toolpusher

    Your area of the country,will still freeze in the winter, if you go in the attic, that could be a problem if it's not a well thought out install. With safties and heat tape.
    Generally true, but if you foam the roof deck instead of doing traditional insulation on the ceiling joists, the attic is just another insulated room and not subject to freezing at all. I believe that's what he intends to do in this case.

    I agree that ultra-high SEER is overkill in this case. The utility rates are low enough that you'll never save enough with the extra efficiency to cover the additional up-front cost you'll pay. The primary heating and cooling should be a mid-range heat pump, either way. The only real question is if the backup heat source should be electric or gas. I'd still prefer electric backup, so in that case the indoor unit would be an air handler. You should be able to get a nice heat pump, maybe 15 SEER, with variable speed air handler. That combination will do everything you want to do (good humidity control, quiet, good comfort, low operating cost), and will cost way less up front than what you'd pay for the G61MPV and 21 SEER setup. It will take a little more juice in the summer than a 21 SEER, but the savings over using gas to heat will more than make up for the difference, even before considering what Lennox is going to want for a 21 SEER AC ($$$, as Lennox would say).

  12. #12
    Join Date
    Jan 2006
    Posts
    25

    summer costs

    Is this representative of longer cooling
    months time vs heating time? i understand your
    explanation, but I can forsee more usage
    in summer or warmer months vs cold winter
    needs..
    thanks, Sr. D

  13. #13
    Join Date
    Nov 2004
    Posts
    2,927
    Originally posted by señord
    But for issues reg. home construction hvac needs, I can only call my cousin to ask what I should do...Thanks to those who posted previously... Dave
    okc is fairly humid. the air conditioner will remove humidity.

    let me rephrase that, air conditioner should remove humidity.if it dont then there is a problem with the system.

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