Thought my home was tight?

[kkmcewen]

Very hot....it was 109 here today. I have a Carrier 16 seer 4 ton infinity heat pump. My home is a 2000 sq ft home with high celings. Set thermostat at 77, and it held there until 3:00p.m.. Then it went to 80 and has not come down yet. I have my unit serviced twice a year and just had it done. Measured the temp out of the return and intake. There is a 18 degree difference at the moment. Since its close to 20, I assumed that its doing its job. So, to my question. If my temp difference is 20, why cant my unit keep up?

[2old2rock]

Outdoor temp is above design temp?
If it is, then your system is probably sized right, and performing properly.

[kkmcewen]

Outdoor temp is above design temp?
If it is, then your system is probably sized right, and performing properly.

I have been told that our design temp for our area is 100.

[paul42]

I know my home is tight.
4,000 sq. ft. 2 ton heat pump, 108 outside, 73.8 inside.

[Texas-Tech]

I know my home is tight.
4,000 sq. ft. 2 ton heat pump, 108 outside, 73.8 inside.

It's either the tightest home in Texas or your pulling my leg, 2 tons isn't gonna do much on 4000 sq ft, much less in Dallas

[karsthuntr]

I have been told that our design temp for our area is 100.

If your design temp is 100 and its 109 and you are 3 degrees above your set point, you are doing good.

[paul42]

It's either the tightest home in Texas or your pulling my leg, 2 tons isn't gonna do much on 4000 sq ft, much less in Dallas

Put the air handler & duct work in conditioned space.
Shade all the windows in the summer.
Make the house air tight.

West end of Fort Worth.
Upstairs, it is 73.9, downstairs is 68.

[Joe Harper]

Your system is designed to deliver its rated btu's up to 100 degrees outdoor temp. . Anything over that emp decreases the output. Basically you have enough btu output to maintain temp at 80, but not enough to bring the temp down...unless you live in a styrofoam house.

[udarrell]

Very hot....it was 109 here today. I have a Carrier 16 seer 4 ton infinity heat pump. My home is a 2000 sq ft home with high ceilings. Set thermostat at 77, and it held there until 3:00p.m.. Then it went to 80 and has not come down yet. I have my unit serviced twice a year and just had it done. Measured the temp out of the return and intake.

There is a 18 degree difference at the moment. Since its close to 20, I assumed that its doing its job. So, to my question. If my temp difference is 20, why cant my unit keep up?

The percent relative humidity has the biggest affect on the indoor temp-split.
The higher the humidity the lower or lesser the sensible temp-split; the lower the humidity the higher the temp-split.

Regarding the indoor split; a higher indoor temp has a much lesser affect than a high humidity level on reducing the split. With a rather high humidity latent heatload a 12 or 14-F temp-split could still indicate a properly operating system.

The 109-F outdoors will reduce the BTUH output of the condenser, maybe a little water misting would help, if combined with a TXV metering device on the indoor coil.

The indoor airflow CFM if too low, in a relatively dry climate, will reduce BTUH performance of the indoor coil.

[bmathews]

It's either the tightest home in Texas or your pulling my leg, 2 tons isn't gonna do much on 4000 sq ft, much less in Dallas

Maybe 2500 of that is an unconditioned garage? I find it hard to believe as well. 2000 sq. ft. per ton? Holding 74 at 109? I've worked on some pretty efficiently built houses and 1000 sq. ft. per ton in Texas is really pushing it.

[precision hvac]

I know my home is tight.
4,000 sq. ft. 2 ton heat pump, 108 outside, 73.8 inside.

Not in your wildest dreams

[Gus-Herb94]

Put the air handler & duct work in conditioned space.
Shade all the windows in the summer.
Make the house air tight.

West end of Fort Worth.
Upstairs, it is 73.9, downstairs is 68.

Are you sure that's not two two ton units? Either way I would love to know your secret. Even if it is perfectly shaded and insulated, sealed etc that still sounds crazy.

[lynn comstock]

kkmcewen, Where are you located? Climate matters, especially humidity (As Udarrel was pointing out).
paul42, That is hard to believe because we expect "normal construction".

• A home that size in a simple rectangle of 40'x50' with two stories would have a minimum gross wall area of 5760 sq.ft.
• The typical window area is 10 to 15% of wall area so the minimum window area for non cave dwellers would be about 576 sq. ft.
• The volume of the home is at least 32000 cu. ft, and the recommended air changes per hour for IAQ reasons is .35 or 11,200 cfm per hour (187 cfm).

Tell us more about the home construction. Is it subterranian? Do you have windows and doors? How are they constructed? Do you have the recommended ACH? Do you have an ERV or HRV?

[paul42]

Are you sure that's not two two ton units? Either way I would love to know your secret. Even if it is perfectly shaded and insulated, sealed etc that still sounds crazy.

It is an unusual house.
The house is on a slope. The top floor is the living quarters and is 2,300 sq. ft.. The bottom floor is storage and mechanical with no windows and only one exterior door.

The bottom floor is all above ground with the exception of the east end which faces the fill under the garage. The bottom floor is the same size as the top floor, but due to the slope of the ground, the ceiling is only 6' at the east end, so I call it 1,700 sq. ft. So, I have at least 4,000 sq. ft. of conditioned space, all above ground.

All of the duct work is in the bottom floor and feeds wall stacks with vents about a foot below the 10 foot ceilings in the top floor.

The house has 3 foot eves and large porches which shade all of the windows on the north & south. The east is shaded by the garage. The west has 3 small windows tucked up under the eves. They have very low e glass and don't get any sun until after 6. The rest of the windows in the house don't see any sun at all during the summer.

The attic has R49 insulation. The walls have 2" of polyiso foam board between the sheathing and the brick, all sealed with aluminum foil tape. I spent a lot of effort air sealing the house while in construction. I sealed the outlets, sealed the top plates, added gaskets behind the drywall, and spent a few hours in the attic with a foam gun before the insulation was blown in. On the walls, between the polyiso foam and the sheathing is a peel & stick roofing membrane that is completely air & water tight.

I heat & cool at least 4,000 sq. ft. with one 2 ton heat pump in north central Texas.

[kkmcewen]

kkmcewen, Where are you located? Climate matters, especially humidity (As Udarrel was pointing out).
paul42, That is hard to believe because we expect "normal construction".

• A home that size in a simple rectangle of 40'x50' with two stories would have a minimum gross wall area of 5760 sq.ft.
• The typical window area is 10 to 15% of wall area so the minimum window area for non cave dwellers would be about 576 sq. ft.
• The volume of the home is at least 32000 cu. ft, and the recommended air changes per hour for IAQ reasons is .35 or 11,200 cfm per hour (187 cfm).

Tell us more about the home construction. Is it subterranian? Do you have windows and doors? How are they constructed? Do you have the recommended ACH? Do you have an ERV or HRV?

I live in Sherman Texas....Just north of Dallas.

[Shophound]

It is an unusual house.
The house is on a slope. The top floor is the living quarters and is 2,300 sq. ft.. The bottom floor is storage and mechanical with no windows and only one exterior door.

The bottom floor is all above ground with the exception of the east end which faces the fill under the garage. The bottom floor is the same size as the top floor, but due to the slope of the ground, the ceiling is only 6' at the east end, so I call it 1,700 sq. ft. So, I have at least 4,000 sq. ft. of conditioned space, all above ground.

All of the duct work is in the bottom floor and feeds wall stacks with vents about a foot below the 10 foot ceilings in the top floor.

The house has 3 foot eves and large porches which shade all of the windows on the north & south. The east is shaded by the garage. The west has 3 small windows tucked up under the eves. They have very low e glass and don't get any sun until after 6. The rest of the windows in the house don't see any sun at all during the summer.

The attic has R49 insulation. The walls have 2" of polyiso foam board between the sheathing and the brick, all sealed with aluminum foil tape. I spent a lot of effort air sealing the house while in construction. I sealed the outlets, sealed the top plates, added gaskets behind the drywall, and spent a few hours in the attic with a foam gun before the insulation was blown in. On the walls, between the polyiso foam and the sheathing is a peel & stick roofing membrane that is completely air & water tight.

I heat & cool at least 4,000 sq. ft. with one 2 ton heat pump in north central Texas.

Paul, do you actively condition what you might call your "basement"? (North Texas homes typically do not have basements, so your house is indeed unusual). IOW are there supplies and returns in the lower level?

With your ducts out of an attic and in conditioned space, and with the type of envelope construction you outline above, I don't think you're trying to pull one over on us. Placing insulation outboard of exterior sheathing, and sealing it, is one of the smartest things one can do with RNC, along with no ducts in the attic and an airtight barrier between house and a ventilated attic.

Were I doing it, however, I'd forgo the "basement" for slab-on-grade and foam the roof deck, along with a low emissivity standing seam metal roof. Radiant barrier on top, insulation directly underneath. Ducts in attic like normal, but the heat gain issue is minimal, since the attic is sealed and insulated. Kill the winter stack effect, kill the radiant gain in summer and reverse stack effect. But that's just my preference.

Of course, sounds like you built into the side of one of our rare hillside lots here in Cowtown.

[mchild]

paul42's history on this site is well documented with a registration date of 2001. Many of his postings had to do with construction issues as the home was being built. The sizing of his system was the center of much discussion at the time and he has been able to provide updated info on the performance of is comfort system(s) that supports his decisions during the construction period. No legs are being pulled.

[tipsrfine]

Paul should start a thread about his homes performance for the benefit of the people who come to this site on advice on the building of thier new homes. Way to go Paul!!!

[paul42]

Paul, do you actively condition what you might call your "basement"? (North Texas homes typically do not have basements, so your house is indeed unusual). IOW are there supplies and returns in the lower level?

With your ducts out of an attic and in conditioned space, and with the type of envelope construction you outline above, I don't think you're trying to pull one over on us. Placing insulation outboard of exterior sheathing, and sealing it, is one of the smartest things one can do with RNC, along with no ducts in the attic and an airtight barrier between house and a ventilated attic.

Were I doing it, however, I'd forgo the "basement" for slab-on-grade and foam the roof deck, along with a low emissivity standing seam metal roof. Radiant barrier on top, insulation directly underneath. Ducts in attic like normal, but the heat gain issue is minimal, since the attic is sealed and insulated. Kill the winter stack effect, kill the radiant gain in summer and reverse stack effect. But that's just my preference.

Of course, sounds like you built into the side of one of our rare hillside lots here in Cowtown.

There is one supply and one return in the basement. The majority of the cooling comes from the uninsulated metal duct work that is located in the lower level. The heat pump water heater in the lower level provides year round dehumidification.

The slab on grade was not an option with this lot, too much slope, several huge live oaks we just had to keep - and they are still doing quite well.

I strongly considered making the attic part of conditioned space, but it just was not cost effective for this lot and house layout. My wife & I really wanted a standing seam metal roof, but the cost was astronomical. My wife is in love with the idea of a rain water collection system and a standing seam roof would have been ideal. Sadly, the dollars were just not there.

[paul42]

Paul should start a thread about his homes performance for the benefit of the people who come to this site on advice on the building of thier new homes. Way to go Paul!!!

Different climates call for different answers, and every lot / home design changes what is cost effective.

For this part of the country, the secrets are
put the air handler & duct work in conditioned space
shade the windows in the summer
Make the house air tight.

There are many ways to achieve it, but those 3 things are critical for an energy efficient house in my part of the country.