Homesteading Forum banner
1 - 20 of 22 Posts

·
Registered
Joined
·
422 Posts
Discussion Starter · #1 ·
Thanks in advance for all who provide guidance.
My wife and I will be building a new home sometime next year. It has cathedral ceilings in living/dining/kitchen area, and 3 bedroom, 2.5 bath, 1700 sq ft heated, plus a 350 sq ft bonus room upstairs, which will be primarily storage.
Home is located in central louisiana, (faces north) where the air condition runs a lot more than the heat, so I'm thinking about going with a high eff ac, and using gas logs as primary heat source. (heat pump is a viable option)
Currently thinking of insulating with icynene spray foam insulation in (6") stud walls and roof.
I do understand there are some variables involving sq ft of window glass, and a few other factors, but I'm looking for a "rule of thumb" guide.

I'm thinking a 2.5 ton 17 seer central unit will do the job...possibly a 3 ton.

opinions?
 

·
Registered
Joined
·
701 Posts
i have about 2200 sf and i have a 4 ton. if i was you i would go with a 3.5 or 4 ton anything less and you will be working it to death IMO. My home is set up a lot like yours 8 foot flat 4 bedrooms and living room and cathedral ceilings in family/dining/kitchen with 2x6 walls.
 

·
agmantoo
Joined
·
10,852 Posts
If you have access to abundant cheap water get a geothermal heatpump. You will get several dollars worth of heat or cool for a dollars worth of power.
 

·
Registered
Joined
·
24 Posts
We use the average of 500 sq. ft per ton. We use Wright J software to calculate tonage, but I don't have access to it. I might could get our member services mgr. to run some calculations since we're fairly close to you.

In my personal home, we have 1800 sq. ft with flat 8' ceilings throughout and have an 18 SEER, 3 ton, 2-compressor, variable speed heat pump from Trane. It has a 1 1/2 ton also, and that comes on if needed instead of running the full 3 tons.

Geothermal is the way to go if you can afford the up-front costs.
 

·
Registered
Joined
·
422 Posts
Discussion Starter · #5 ·
We use the average of 500 sq. ft per ton. We use Wright J software to calculate tonage, but I don't have access to it. I might could get our member services mgr. to run some calculations since we're fairly close to you.

In my personal home, we have 1800 sq. ft with flat 8' ceilings throughout and have an 18 SEER, 3 ton, 2-compressor, variable speed heat pump from Trane. It has a 1 1/2 ton also, and that comes on if needed instead of running the full 3 tons.

Geothermal is the way to go if you can afford the up-front costs.
more info:
I checked deeply into geo, and found that Geothermal is not cost effective. The high up front costs cannot be recovered in less than about 12 to 15 years +/-. When you add in maintenance costs, it gets worse.
That long payback makes geothermal a no-go. So, I'm only considering regular type units now.

Also, keep in mind the spray foam insulation, that virtually eliminates air infiltration, and has a high r value. I've been told that spray foam reduces the ac tonnage requirement significantly.

Thanks again.

b
 

·
Registered
Joined
·
24 Posts
Actually, geothermal is very efficient. I work for an electric utility and we actually push these to reduce costs. Our general manager has had one for 20 years with no problems.

We have true 6" exterior walls and reflective insulated house wrap and reflective siding with blown in rockwool insulation. Even though the home is efficient, you can still save money. My highest electric bill ever, was this past August or September at $264.

Your a/c and heating is something you don't want to cut corners on. At least investigate the heat pumps. When we built we did everything my company recommended during the building process. If you live on an electric coop's power lines, they should have someone there that will walk through you with it, and give an energy audit as well as tips.
 

·
Registered
Joined
·
701 Posts
Actually, geothermal is very efficient. I work for an electric utility and we actually push these to reduce costs. Our general manager has had one for 20 years with no problems.

We have true 6" exterior walls and reflective insulated house wrap and reflective siding with blown in rockwool insulation. Even though the home is efficient, you can still save money. My highest electric bill ever, was this past August or September at $264.

Your a/c and heating is something you don't want to cut corners on. At least investigate the heat pumps. When we built we did everything my company recommended during the building process. If you live on an electric coop's power lines, they should have someone there that will walk through you with it, and give an energy audit as well as tips.
How big is your house? and why so high on the ele. bill? just wondering.
 

·
Registered
Joined
·
24 Posts
It's 1800 sq. ft. all electric. We have a marathon water heater also which is supposed to be efficient as well. Our biggest user was a 7 year old dryer. The usage was I believe 1900 kwh plus a $14 security light so it was actually 250 or so.

We have two small children, and live in the country life with farm animals so we normally wash/dry 2 loads of clothes daily, pretty much every day of the week, water well for pasture, and running a 240v welder.

We actually purchased a new front loader washer/dryer in October and our usage dropped tremendously. I am graphing our meter every 15 minutes and our daily usage has dropped rather significantly. Usage this month will be less than 1000 kwh.

Our lifestyle I guess you would say is the reason for increased usage. Two small children under 5 learning to turn lights off, close doors, etc. is fun.

The average kwh consumption on our system is probably around 1200-1500 kwh per household on 1500-2000 sq. ft. home, I'm estimating.
 

·
agmantoo
Joined
·
10,852 Posts
I am sitting here nice and toasty and it is 28 F outside and going to 19 F. The house is 2900+ sq ft with a 9 ft ceiling and built over a full basement and with no insulation in the floor. Hurd windows, six inch walls and heavy overhead insulation. The geothermal pump was serviced once about six months after installing due to a problem with a solenoid valve that shuts the water off. The geothermal unit is now 16 years old. It is sized to just fit the house needs. It is a big mistake to oversize a heatpump as it negatively impacts the efficiency. My system is 3 1/2 ton. I have never had a monthly power bill for the entire home for more than $150. You are aware that you can get your domestic hot water off the geothermal unit during the AC use months? The savings are enough to offset a significant amount of mortgage. Personally, I would not want a home without a geothermal system. My setup is not a loop system and there is a small efficiency gain there as the ground water temperature is better for the needs than the water through a loop. With a geothermal unit everything is inside so there is no corrosion problems with the components thus the metal lasts and lasts. I would reconsider!
 

·
Registered
Joined
·
24 Posts
I apologize. I just remoted into my office and it was $244 at 1872 kwh less $14 for the security light. It was also in June which was our hottest peaking month here. I'm a little off tonight I guess. Close though. ;)
 

·
Registered
Joined
·
422 Posts
Discussion Starter · #11 ·
I am sitting here nice and toasty and it is 28 F outside and going to 19 F. The house is 2900+ sq ft with a 9 ft ceiling and built over a full basement and with no insulation in the floor. Hurd windows, six inch walls and heavy overhead insulation. The geothermal pump was serviced once about six months after installing due to a problem with a solenoid valve that shuts the water off. The geothermal unit is now 16 years old. It is sized to just fit the house needs. It is a big mistake to oversize a heatpump as it negatively impacts the efficiency. My system is 3 1/2 ton. I have never had a monthly power bill for the entire home for more than $150. You are aware that you can get your domestic hot water off the geothermal unit during the AC use months? The savings are enough to offset a significant amount of mortgage. Personally, I would not want a home without a geothermal system. My setup is not a loop system and there is a small efficiency gain there as the ground water temperature is better for the needs than the water through a loop. With a geothermal unit everything is inside so there is no corrosion problems with the components thus the metal lasts and lasts. I would reconsider!
That's great information agmantoo. My problem with the geothermal unit is the initial cost of $22,000 using a loop system. A vertical system is even more expensive. At the same time, I can have a 3 ton heatpump installed for $7,000 to $8,000 depending on brand, features, etc...
That's 60% less money. Even when you spread that cost out, the return on investment is really low at today's energy costs plus an inflationary bias.
After reviewing those numbers, the decision became much easier. I love the efficiency of the geo units, but the cost is insurmountable at this time.

Thanks for your input

b
 

·
Dallas
Joined
·
13,903 Posts
How big is your house? and why so high on the ele. bill? just wondering.
High? thats low for Summer in Texas. I'd love to have that small an electric bill in July or August, mine is usually in the $350 to $400 range for a 2200 sq ft house. Course the AC is about 12 years old and they don't insulate houses down here like they do up north. I've got extra insulation in the attic but nothing you can do about brick walls without tearing apart all the interior walls and rebuilding them. Planted some shade tree's that'll help when they get big enough but thats a few years away yet.

Here's July
07/30/08
average temp = 99
KWH = 2643
Amount = $353.06
 

·
Premium Member
Joined
·
1,569 Posts
All I know is I have to replace mine , went out this weekend. Going to cost $4000
 

·
Registered
Joined
·
2,193 Posts
Bear in mind that in a hot climate, it is possible to have too BIG a unit also. Then it doesn't run enough to dehumidify, which is important in the Deep South.
 

·
Registered
Joined
·
701 Posts
High? thats low for Summer in Texas. I'd love to have that small an electric bill in July or August, mine is usually in the $350 to $400 range for a 2200 sq ft house. Course the AC is about 12 years old and they don't insulate houses down here like they do up north. I've got extra insulation in the attic but nothing you can do about brick walls without tearing apart all the interior walls and rebuilding them. Planted some shade tree's that'll help when they get big enough but thats a few years away yet.

Here's July
07/30/08
average temp = 99
KWH = 2643
Amount = $353.06
well it gets hot here to and my highest bill was $180, $80 last month for 2200 + sq. ft. I do have thermal windows and the cfl lights.
 

·
Premium Member
Joined
·
7,215 Posts
About 7-8 years ago when I was last in the market, they were recommending one ton of capacity for each 600 square feet of cooled space. The seer's are much higher now, and I'm not sure how that would impact sizing.
 

·
Registered
Joined
·
422 Posts
Discussion Starter · #17 ·
I believe that 500 to 600 sq ft to the ton is about right for regular construction. I am mostly interested in how much difference the spray foam insulation would make to that number. I'm thinking that 700 to 800 sq ft to the ton would be about right, but I'm not certain.

b
 

·
Registered
Joined
·
701 Posts
I believe that 500 to 600 sq ft to the ton is about right for regular construction. I am mostly interested in how much difference the spray foam insulation would make to that number. I'm thinking that 700 to 800 sq ft to the ton would be about right, but I'm not certain.

b
You also should think about heat from lights, people, dogs, cats, etc.
 

·
Registered
Joined
·
2 Posts
I know this is a late post on this thread but please, if you are building a new home, take the time and money if necessary and require your HVAC contractor to do a room by room Manual J, then design your duct system using Manual D and choose your system using Manual S. In cooling climates your AC will be your largest energy user and it pays to size it properly. Rules of thumb for sizing AC are no longer valid. Every improvment you make to your envelope reduces your cooling load. I'm a state certified energy rater here in FL and teach builders and HVAC contractors how to build ENERGY STAR Qualified Homes. I also do manual J calculations. In newer homes with multiple upgrades to the envelope I'm seeing 1 ton of AC for up to 1,000 sq. ft. Oversized systems will not remove the humidity because they do not run long enough. A properly sized unit should run 20 min per hour when your temperature is at your areas design temp. On those few days a year when outdoor temps are higher than design the unit will run almost continously and that is the way it should operate. Much like your car AC, the longer it runs the better it cools and the more efficiently it operates.
 

·
Registered
Joined
·
2 Posts
The new Manual J 8th edition, says the design temperature for an area is a temperature that for 99% of the year it is at or below that temp for cooling purposes and the opposite for heating. For Louisana design temps range from 91-96 degrees based on the area.

The reason you want the Manual J room by room done, is it calculates based on orientation, occupancy, and electronics exactly how many cubic feet of AC you need to cool each room. It keeps your home from having "hot" rooms.

I've seen everything imaginable even in new construction. Manual D, duct design will guarantee that all the cubic feet of air your system pushes will be distributed throughout the home and returned. I did one new home that had 1200 cubic ft of air being pushed into the home but the return could only handle about 1000 cubic feet. The air screamed trying to get through that return!

HVAC isn't for amateurs. It is highly complex. I would never higher an AC contractor who sizes systems by a rule of thumb. A pro knows how crucial it is to do a Manual J and size properly.
 
1 - 20 of 22 Posts
Top