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  1. #1

    2nd story heat issues -- solutions w/o new unit?

    Hi


    I have a 2 story house with an open starcase. The bottom floor is always cool and but the top floor is always a bit harder to keep cool. Recent 100+ temps have caused the second floor to stay warmer for longer. Second story unit runs constantly to keep the second floor cold.
    My heat load on the second floor is high due to heat rising as in most houses – there are no doors to stop the airflow.

    The first story unit is oversized and cools the house quickly -- 20 degree drop
    The second story unit is slightly oversized and working fine - 17 to 20 degree drop.

    So can I “fix” my issues with something other than a new unit???

    Any thoughts on these ideas?

    1 -- Add or move first floor return to the middle or top of the staircase? The thought is that I would pull the hot rising air back down to the first floor unit.

    2 --Place a duct in the staircase from the first floor unit? I guess a large one? Second floor return is at the very top of the staircase

    3 – solar attic fans – remove heat from the attic – not a house fan.

    4 – Install a ceiling fan in the staircase.

    5 – add a portable A/C unit for master bedroom

  2. #2
    Join Date
    Aug 2003
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    Fort Worth, TX
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    Quote Originally Posted by wobblybowl View Post
    Hi


    I have a 2 story house with an open starcase. The bottom floor is always cool and but the top floor is always a bit harder to keep cool. Recent 100+ temps have caused the second floor to stay warmer for longer. Second story unit runs constantly to keep the second floor cold.
    My heat load on the second floor is high due to heat rising as in most houses – there are no doors to stop the airflow.

    The first story unit is oversized and cools the house quickly -- 20 degree drop
    The second story unit is slightly oversized and working fine - 17 to 20 degree drop.

    So can I “fix” my issues with something other than a new unit???

    Any thoughts on these ideas?

    1 -- Add or move first floor return to the middle or top of the staircase? The thought is that I would pull the hot rising air back down to the first floor unit.

    2 --Place a duct in the staircase from the first floor unit? I guess a large one? Second floor return is at the very top of the staircase

    3 – solar attic fans – remove heat from the attic – not a house fan.

    4 – Install a ceiling fan in the staircase.

    5 – add a portable A/C unit for master bedroom
    (Stand by for possible posts from BrianC and Xavier heralding return air grill location as the great HVAC air balance savior. )

    Of the five items listed in your post, only one of them I might consider doing. It's best I first ask more information from you regarding your house:

    1. Year structure was built (if known)
    2. Depth of insulation in attic, and insulation type
    3. A/C supply duct run locations (basement, attic, crawl space, dropped ceiling, etc.)
    4. Orientation and type of windows throughout house (single or double pane glass, shaded or in the sun, etc.)
    5. Amount and type of ventilaiton already in attic (soffit/ridge/gable end vents, etc.)
    6. Ceiling penetrations into attic, such as recessed (can) lights, etc.
    Answering the above questions will help target advice to give you regarding your "thermal envelope" which is the shell of your house that serves as a barricade between you and the outdoors. Heat rising on the interior of a two story house is only part of the problem. Many other factors contribute to uneven cooling and heating between floors. Your solution does not automatically warrant a new a/c system.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Thank you

    Year structure was built (if known) 1973
    Depth of insulation in attic, and insulation type - 6 inches blown in 2 years ago
    A/C supply duct run locations (basement, attic, crawl space, dropped ceiling, etc.) - all attic
    Orientation and type of windows throughout house (single or double pane glass, shaded or in the sun, etc.) - mostly shaded house except west 2nd floor. all windows east west. Have solar screens on full sun exposed windows. Single pane mostly
    Amount and type of ventilaiton already in attic (soffit/ridge/gable end vents, etc.) ridge --at top of the roof.
    Ceiling penetrations into attic, such as recessed (can) lights, etc. Many can lights 15 -- 5 are not air tight, 3 vent fans

    also all rooms have ceiling fans

  4. #4
    Join Date
    Feb 2008
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    six inches of attic insulation is not a whole lot IMO

    single pane windows are killer!

    can light leak alot of unconditioned air into a structure if the structure should be in a negative pressure.

    what kind of access do you have to the attic and how well is it sealed?
    If Guns Kill People, Do Pencils Misspell Words?

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  5. #5
    Join Date
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    Quote Originally Posted by wobblybowl View Post
    Thank you

    Year structure was built (if known) 1973

    The year of the first energy crisis.

    Depth of insulation in attic, and insulation type - 6 inches blown in 2 years ago

    Was this six inches blown on top of something else, or was there nothing on the attic floor before this was blown in? If there was, what is the total depth of insulation in your attic?

    A/C supply duct run locations (basement, attic, crawl space, dropped ceiling, etc.) - all attic

    The worst place for a/c ducts to be, but you work with what you got. Is the furnace/air handler also in the attic? One thing to check regarding ducts in an attic...at some point they must penetrate the ceiling to blow air into the house. This penetration is an often ignored point of air leakage into and out of your house. Pull the vent grill off...if you see a gap between the sheetmetal and the drywall, seal it (I prefer water based HVAC mastic over caulks). Do this to every penetration in the ceiling caused by ducts.

    Orientation and type of windows throughout house (single or double pane glass, shaded or in the sun, etc.) - mostly shaded house except west 2nd floor. all windows east west. Have solar screens on full sun exposed windows. Single pane mostly

    The solar screens help, but low e glass (double pane, argon filled) with non metallic frames will perform better on walls that can't easily be shaded. I have recorded between a 12 to 15 degree temperature differential across a low e double pane assembly where the outer glass assembly was over 100 degrees F. Even fully shaded single pane glass units can't come near touching that. At best they will read almost right in the middle between the indoor temp and the outdoor temp, indicating a good amount of heat transfer occurring through the pane.

    Amount and type of ventilaiton already in attic (soffit/ridge/gable end vents, etc.) ridge --at top of the roof.

    No soffit vents? Ridge vents without soffit vents are crippled vents.

    Ceiling penetrations into attic, such as recessed (can) lights, etc. Many can lights 15 -- 5 are not air tight, 3 vent fans

    Use caution sealing these fixtures due to high heat produced by incandescent bulbs.

    also all rooms have ceiling fans

    Ceiling fans are most efficient when someone is in the room with it. With the exception of a ceiling fan installed at the top of your stairwell between floors, it's best to leave a ceiling fan off when nobody is in a room.
    The idea behind my line of questioning in my OP and this one is to encourage you to think more deeply of possible sources leading to your upstairs discomfort and energy consumption apart from the HVAC system. While a properly sized, installed, and tuned HVAC system plays a major role in whether you will be comfortable or not (and whether you'll survive electric bills in the summer without a cardiac arrest), the building envelope's performance is the other major player in this scheme. Your occupancy habits of the structure also count, but not as much as the other two mentioned.

    At best we can only give generic advise for your house and HVAC system, since we're not on site. Nevertheless it is very common to give the a/c system the evil eye when things aren't going well indoors, when the house itself should be more closely examined.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Insulation was blown in over a paper thin layer of rockwool

    yes sorry ridge vent and sofit vent

    all ductwork and buckets sealed

    so the suggestion is new windows?

  7. #7
    Join Date
    Aug 2003
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    If money is tight, my thought is to tackle worst offending windows vs. replacing every window in the house at the same time. I'm hearing west facing wall with no shade, that is where I would be all over replacing windows.

    Long term, consider ways to shade the west facade. Plant some trees, consider a trellis, any feasible way to provide shade for the wall and windows will help considerably. Short of that, single pane windows facing west will be the worst offenders for dumping heat into your house in summer. Especially if the area of glass is considerable, as I often see in many new houses built around here (insane!).
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
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    Beautiful, Philadelphia, the City of Brotherly Love!
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    Let me add a few more questions.
    Is the return ducting sealed? Is the return central (one location), or are there individual returns in each room?

    I find open filter racks, returns drawing out of soffits that have openings into the attic, etc.

    Those light cans, are they insulated over? I can't believe electrican's install these open fixtures into attics, most times they push the insulation away from the fixture as well.

  9. #9
    Everything is sealed tight, had that done already and I inspected

    When the insulation was blown in they placed circular rings around the can lights to prevent insulation form touch them. So no they are uninsulated

    Doors and attic access have weatherstriping

    Replacing the window is kind of costly it 7" h by 6" long but it gets west sun.


    So can I rule out the solar attic fan as an option, thats about $500.

  10. #10
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    Quote Originally Posted by wobblybowl View Post
    Everything is sealed tight, had that done already and I inspected

    When the insulation was blown in they placed circular rings around the can lights to prevent insulation form touch them. So no they are uninsulated

    Doors and attic access have weatherstriping

    Replacing the window is kind of costly it 7" h by 6" long but it gets west sun.


    So can I rule out the solar attic fan as an option, thats about $500.
    Is this 7' x 6' window on the west wall upstairs or downstairs?

    Here's a way to get a rough idea how much heat that 42 square foot hole in your west facing wall is dumping into your house:

    Basic heat transfer formula:

    U factor * Area (in square feet) * temperature difference = BTUH/sq. ft.

    To simplify, let's assume the 42 square foot window is in a west facing wall that measures 15 feet long by 8 feet high. Total exposure of west facing facade is 120 square feet. Of that 120 square feet, 42 square feet is single pane, metal frame window. 65% of the wall is insulation, studs, top & bottom plate, drywall, exterior sheathing...we'll give this percentage an assembly R value of 11. The reciprocal of R value gives U factor, which we need for the formula above: U factor for wall will be .09. The remaining 35% west facing square footage is single pane glass, which the ASHRAE Handbook of Fundamentals assigns a U factor of 1.23.

    Assumptions will be exterior surface temperature of glass and exterior siding are the same, 110°F. Interior air temperature is 75°F. This makes our temperature difference, or delta T, to be 35 degrees.

    Rate of heat transfer through wall:

    .09 * 78 * 35 = 246 BTUH

    Rate of heat transfer through window:

    1.23 * 42 * 35 = 1801 BTUH


    Wow. I actually crunched the window figures twice to be sure I didn't hit a wrong key or something. That's right...the window is dumping over seven times the amount of heat into the room as the larger area of insulated wall. That is not even including the warming effect the direct rays of the sun streaming through the glass have on whatever it strikes, assuming anyone would be insane enough not to draw the curtains closed over that window on a hot summer day.

    Now, let's rip out that single pane window and plug in a double pane, low e, argon filled, non metallic job (aka insulated glass assembly, or IGA) with a U factor of .30.

    .30 * 42 * 35 = 441

    While this window still underperforms the surrounding wall, it shaves 1360 BTUH of heat gain into your house off! That is nothing to sneeze at.

    And we just crunched numbers for summer heat gain. In winter, where wider delta T's often exist between interior and exterior, the heat transfer differences would be even greater.

    Window replacement, while not cheap, will reap significant differences in comfort and energy use. It's in the physics of the thing.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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