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  1. #1
    You guys probably hate questions like this, but I need to have some idea of whether I'm getting BS from the contractor.

    I have a section of my house that is 624 sq ft (outside dimensions) which consists of one large room and one tiny bathroom. The main room has a ten foot ceiling. This room is less than two years old and seems reasonably well insulted: 2x4 walls with fiberglas batting and fiberglas in the ceiling that is at least 16" deep. Three of the four walls are outside walls.

    During the afternoon, with outdoor temps in the high 80s or low 90s, the temp of the main room will not drop below 76-77F with the heat pump running continuously. The heat pump is a 1.5 ton unit installed less than a year ago. The air coming out of the ducts is about 58 degrees or so. The filter is new.

    Given the duct temp, I'd say the unit is probably working ok which makes me think it might be under sized, but 624 sq ft doesn't seem too large for a 1.5 ton unit. I'm curious as to how much additional capacity is required for a 10 foot ceiling versus an 8 foot ceiling.

    I'd be grateful for comments that might help me get a little perspective on this.

    Thanks!

    -Dave

  2. #2
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,644
    I think the unit is the correct size, i would say it was sized to maintain 78 degrees. See how it works if you set it to 74 and dont touch it. Shade your windows?
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  3. #3
    Join Date
    Aug 2003
    Location
    Henderson, NV
    Posts
    209
    Is there a return in this room or is the return elsewhere, the split temps sound correct 20 degrees, it should cool down properly,according to what you posted, the scenario doesnt pan out, that room should be an ice box.How many air vents are there?

  4. #4

    More info

    I have the thermostat set to 72. The unit runs continuously until the sun goes down, when it is finally able to catch up.

    The room has four vertical sliding windows with double pane glass (36"W x 52"H), plus there is a smaller window in the bathroom (24"W x 36"H). The windows are all covered with white aluminum blinds that are closed so that no direct sunlight is coming it.

    There are 5 ceiing vents in the main room and one in the bathroom. There is an additional vent in the stairwell, but I've had it shut while I've been experimenting. I also have both doors shut so the other parts of the house don't add any load to this system, although I don't see much of a difference whether the doors are open or closed.

    The air intake is in the center of the ceiling of the main room and is 24"x24".

    The temperatures of 76-77 are without any of the fifteen 75 watt recessed lights turned on. In fact, there is no electrical equipment generating any heat in the room.

    This is a second story room and the rooms below are cooled.

    The room is to be used as a part time photography studio and during a shoot, I am very actively moving around. At 77F, I'll be drenched in sweat.

    Was I wrong in assuming that heat pumps are usually sized to get lower temperatures thn that? If this unit will only get the room down to 77, I'll have to get a bigger one. And I it's not even 2 years old! I had this room added to the house so I wouldn't have to shoot in the hot old garage anymore.

    -Dave

  5. #5

    Pictures of the room

    Hmmm... I have pictures of the room on my website here in case it would help. It's the top 5 pictures. The pictures are through a wide angle lens, so the room might look a little bigger than it is.

    http://www.kruegerphoto.com/studio.htm

    -Dave

  6. #6
    Join Date
    Jul 2005
    Posts
    2
    Are the fifteen recessed lights a sealed housing type, preventing air infiltration from the space above? If they are rated for direct insulation contact, they probably are sealed fairly well. If they are not rated for direct insulation contact, they are probably full of holes, allowing hot air from above to enter the space. Do you run the exhaust fan in the bathroom continuously? If so, it could be pulling hot air from above the recessed lights, through holes in the light housing, and into your space. Is there an attic or crawl space above the ceiling?

  7. #7
    Join Date
    Jul 2005
    Posts
    2
    Nice studio. Is that pull down stairs in the center of the ceiling? Is there attic space up there? Can you see the recessed light housings from up there? How well are the pull down stairs sealed at the ceiling? Could be another air infiltration avenue.

  8. #8

    Recessed lights

    The recessed lights are closed. They are rated for contact with the insulation and are in fact covered by it (by several inches).

    The pull down ladder makes a pretty tight fit to the frame, but there is no weather stripping, if that's what you mean.

    There is a floor in the attic adjacent the pull down ladder which is less insulated than the deep blown in insulation around it. I think there is batting under the floor. The ceiling joists are 2x8s and the batting is pretty thick.

    The attic is pretty hot. In fact, I probably don't have a thermometer that goes up high enough to measure it. I'm guessing it might be 120-130F. How much help are attic fans? I have two large mushroom vents in the attic and numerous sofit vents. Replacing one or both of those vents with attic fans would have to be cheaper than changing out the heat pump. The air handler is up there, so it's subjected to that heat...

    -Dave

  9. #9

    Right now it's 77F.

    Outside temp is 93F.

    -Dave

  10. #10
    Join Date
    Mar 2005
    Location
    South/West of Quebec in the other part of Canada
    Posts
    2,331
    You have a heat gain or an infiltration problem, you didn't mention a vapor barrier, are you direct sun light? what is your exterior material? do you feel a draft when it is windy?

  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,644
    If you have your photo equipment running and all those lights on i guess you have surpassed the ability of the unit to keep up. Maybe you could add a mini split to you room to assist the unit.

    http://www.sanyo.com/industrial/HVAC/
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  12. #12

    Post In direct sun.

    The walls are 2x4s with fiberglas batting. Sheathing is OSB with hardiplank (fiber cement) siding. No vapor barrier or house wrap. Interior is just regular 1/2" sheet rock.

    I don't know if I would notice any infiltration during the summer, but we don't have any trouble keeping it warm during winter. I don't feel any drafts and the outside is well caulked with silicone. Of course, lap siding is not going to be completely air tight, but there's practically no furniture in the room so it's pretty easy to see there is no place that air is likely to get into the room from the outside. The windows seem to have a pretty good seal, as well.

    I thought it strange that they didn't use any house wrap, but I thought they knew more than I did, so I didn't complain. In fact, I comepletely removed all the siding and sheathing from the old part of the house and replaced it with OSB and fiber cement so the whole house is now like that. But, the old part of the house isn't having a problem staying cool even with a 32 year old heat pump...

    One thing I noticed is that you have to get your hand right up at the vent to feel much air flow. The old part of the house seems to blow harder through the vents. Maybe there's something wrong with the fan speed on the air handler...

    Is it safe to say that under most circumstances 1.5 tons should be sufficient for a room this size?

    -Dave

  13. #13
    Market man,

    I don't even have the room lights on. In fact, the only electrical equipment operating in the room is the thermostat and the fire alarm.

    -Dave

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