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Old 02-13-2013, 09:05 PM   #16
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Will the size of my ducts have to be changed?


I was watching the sun today relating it to my house. The rear faces east. Sun hits the clear glass patio door & windows around 7am to 11am. Neighbor behind me and over one has a two story house blocking the sunrise a little longer. Southside has no windows/doors. Northside gets no sun. West side (front) starts seeing sunlight on windows around 2 pm to sunset. Entry door is set back 2 ft in so door gets no sun exposure. No wonder my house is so cold when the heater is not on. Duh?

Attached garage is on northwest side blocking half the west side sun exposure. Eaves all the way around 1st and 2nd story are 3' deep with 2x8 facia so it blocks some sun. Two small 14x33 windows at the top of stairs are blocked from the sun partially by facia. I have a 95x33 window on southside 2nd story that gets sun all day. My point to all of this is that for a residential house I think it is positioned pretty good to ward off sunlight.

I have to figure out my next move to get this rolling. I have to find someone to work with me designing a ducting system,where to place supply/returns and an A/C unit. Just randomly calling a contractor is not going to work because most want to come in, do it all in a few days and be gone. I am trying to do as they say," Measure twice and cut once".

I just cant believe my neighbors have a 3 bedroom house with a 3 ton unit, one has a two story with a 4 ton unit and the last one is a two story with a 5 ton unit. Mine calculates out at 1.5 tons?

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Old 02-13-2013, 09:37 PM   #17
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Will the size of my ducts have to be changed?


1.5 tons.... yup,,, its hard to believe...

but its all about the target temps and run times at the target temps.


so lets look at the hottest day and what your hvac system will be doing.

lets say that between 2pm and 4pm it is 80 degrees outside (your summer outdoor target temp) and 75 degrees inside. Your system is designed to run 100 percent of the time with these conditions (in this case between 2 and 4 pm). so you are saying... I dont want my ac running all the time!!!! well, thats the misconception. HVAC systems do not become effecent until at least 10 minutes has passed while they are running. The initial start up is a huge rush of current, but after that the pressures etc equalize and the amount of energy levels off at a fairly reasonable rate. so yes, your ac system will be running a lot at your target temp. but you will be saving the start and stop costs that others are paying.

The next idea to get your head around is when the outside temp is not at 80, but lets say 78. At this point, you should start to hear the system cycle, still more on then off, but the run times should still be fairly long. with an oversized system you will be running very short times, never long enough to get into the economy zone and believe it or not that start stop process is hard on the equipment.

the closer you get to your indoor and outdoor target temps matching, the shorter your run times will get until you dont need the hvac (temps indoors and outdoors the same)... .

so what if the outside temp is 82 (2 degrees above your design temp)..well your system will not be able to keep the house at 75 degrees for the time period that it is 82 degrees outside. it may only keep the inside 76 degrees. +-


so now lets look at your neighbor with the 4 ton system. His system, at the 80 degree outdoor target temp and 75 indoor temp, will run a very short time. chances are it will never get past the 10 minutes of hard running. His bill will be higher. The energy to start it and then stop it and then start it etc will be more then yours which ran for 2 hours in the heat of the day. His system will not last as long as yours will.

so now comes a bit of the magic and your input into the design.... the question becomes, is 75 degrees enough to keep you cool?? if not, change that number in your calculations... maybe 78 is cool enough for you... you could put that numnber in.. also think about other heat loads... do you have massive parties in the afternoons with kids and friends running in and out... well, your hvac system may not be able to keep the house at 75 degrees.. but do you want to oversize your system for that occasion??? there are lots of pieces to this, but its my understanding that the manual j is very well done and will work for you!!!

now lets look at my system

2500 sq feet, 115 outdoor design temp, 75 degree inside temp, design calcs say 3.5 to 4 tons.. I have 5 tons and the longest run I have is about 30 minutes when its 119 out. so my system is oversized (I joke to my family that our ac system will keep the house cool when its 146 degrees outside as per the manual J!!)it also costs me more to run then it should.. I found all this information after I had a new system put in. We went from a seer 10 to 14 and the utilities increased!!!

Have fun and remember this is not rocket science, you will have to make compromises and in the end, you will sleep well at night being an informed consumer.
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Old 02-13-2013, 11:03 PM   #18
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Will the size of my ducts have to be changed?


Thanks for that explanation bobinphx! Trying to understand something here. When I did the Manual J calcs I just inserted the name of my city where I live and the program gave me the Design Conditions.

1.) So are these the recommended temperatures to keep the inside of my house comfortable and to have a 1.5 ton unit run the most efficient?

And as far as having fun I am like you. I have a mechanical brain. For instance with my house I kept wondering where I could run return ducts because this house has never had air. So the old heating duct that transitioned up to the 2nd floor attic is set between the vertical studs so the return can just go up between the studs right next to it. I had a feeling that the existing vertical duct probably was leaking just because work that cant be seen is usually hurried and the drywall covers it. Sure enough the duct was never sealed from day one so heated air has been coming out since 1965 when it was built. I wonder how much. The ducts are 48 years old. Time to throw them out.

For me personally the challenge is more fun than the end result but in this case I will come out of this very comfortable during the hot weather.

2.) If you have any recommendations on what brands a/c - heater units to buy I am all ears. I dont know if you have an extensive background in this area but it sure sounds like it. I cant wait to tell someone I need a 1.5 ton for my two story house.

3.) I intend on using rigid supply duct again. Is it also better to run the rigid return duct?

I also learned from the Manual J calcs I can add some batts in my attics to go from R 11 to R 19. Every little bit helps. I cant believe your summer temps in Arizona.
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Old 02-14-2013, 01:22 PM   #19
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Will the size of my ducts have to be changed?


1st floor drawings of my floor plan
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Old 02-14-2013, 01:45 PM   #20
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Will the size of my ducts have to be changed?


2nd story floor plan - "W" stands for windows - "S" is for existing heating supply registers. 1st floor attic entry is small entrance door in right upstairs bedroom. I was thinking of putting new rectangular supply registers closer to windows which seem to get the most heat coming through the glass.The bedroom on the right gets full sun exposure all day long being its on the south side. East window in the other room gets full sun from sunrise until 11 am. Two small windows side by side on west side get very little direct sun but exposure is from about 2pm until sunset.
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Old 02-14-2013, 01:51 PM   #21
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Will the size of my ducts have to be changed?


I too think that is oversized. I have a two level 2800 sq. ft. home and I have a 3 ton heat pump. I do live in a warmer climate though, Southern Missouri, and the winters are not very cold. (it's 62 here today)
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Old 02-14-2013, 01:58 PM   #22
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Will the size of my ducts have to be changed?


west side (front). ridge vents for roof,turbine vents which I have been told need to be removed, skylight, solar tube, front door is set back 2' from west wall,eaves are 3' deep underneath, 2 x 8 facia and double pane windows. The 2 bd rm windows and window by porch start getting sun exposure around 2pm until sunset, 2 small windows up on 2nd story dont get much sun.
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Old 02-14-2013, 02:10 PM   #23
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Will the size of my ducts have to be changed?


east side - all windows/patio door get sun from sunrise to 11am. Window up above on west side gets full sun all day long. Patio door is dbl pane too. I took this picture at 1130am and you can see everything is already in the shade. My 1st brick planter job at my house in 1986. Not bad for reading a book to learn how to do it.Those bricks fell off a bldg in a Calif earthquake and they were giving them away if you just came and got them. 27 years later I wish I had left them. Ha ha
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Old 02-14-2013, 02:23 PM   #24
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Will the size of my ducts have to be changed?


1965 pull chain dampers
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Old 02-14-2013, 02:44 PM   #25
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Will the size of my ducts have to be changed?


You are looking in the attic through 2nd story bedroom attic door. You are looking at 24" plenum with one 8" branch running around 1st floor attic feeding several 6" supply registers.

When I 1st moved into this house the top of that 24" plenum was open like a can of tuna where the lid starts lifting when you have a couple more turns before its open. I had to push lid back down and seal it. How long did those people I bought my home from wonder why the house was not getting warm?

The one that is capped off was another 8" duct that fed the 2nd story but I am replacing all the duct so I took it out. I live alone so I dont need heat on the 2nd floor right now. The next picture is the closet of the 2nd story bd rm. I had to open the wall to take out the rectangular duct that was never sealed right from the moment they installed it in 1965 so it has been leaking heat FOREVER.

In the next picture u will be able to see where I will be running the new return ducts in between studs right next to where old supply duct ran. I love this kind of work.

I want the new unit right where the 24" plenum is. I dont want it closer to this 2nd story bd room in case it makes any kind of noise
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Old 02-14-2013, 02:50 PM   #26
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Will the size of my ducts have to be changed?


2nd story closet - where the pink foil is the old duct ran there and rose vertically. To the right is where the foil is showing and the return will go in between those studs. I will have new ducts and a new unit = a happy man
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Old 02-14-2013, 02:52 PM   #27
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What a beautiful house! I wish more people in Vegas would take pride in older homes like that but it just doesnt happen here, its a dump.

Your neighbors may not have had a manual j ran when they did their systems, hence the wide range of sizing, many people are affraid to go too small.

Many people here have told me that 3 tons will not cool my 1835 sq ft home in Vegas, we currently have a 4 ton unit but it will work. I have a crane scheduled for this weekend and will be doing the swap. I also blew a ton of insulation into the attic and completely sealed all of the ductwork.
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Old 02-14-2013, 05:53 PM   #28
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Will the size of my ducts have to be changed?


Thanks for the compliment. I bought this house in 1986 as a fixer upper. I did everything you see in the pictures,landscape,windows,lighting,roof,skylight, solar tubes,painted it twice and on and on. I just stole all the ideas of the newer houses in the area,took off the old looking design and now it has great curb side appeal.

If I did not know how to do something I kept asking questions. Most everything is paid for because I did the work. I have some things to still do to seal my house up tighter like fireplace,more batts in the attic,front door seal,etc,.. All the things I should have done long ago.

1.) Are you changing 4 ton to 3 ton because the 4 ton needs replacing?

2.) I put a swamp cooler in here years because I could just never afford a complete AC unit, That cooler kept this house very comfortabe unless it was a humid day. We don't get humidity that often. But for $350 I used that unit for 10 years. And my electric bill did not go up much.So I am pretty certain a 1.5 ton unit will work fine. My kids are grown and gone. It is 99.5% of the time me just living here so I should be fine.
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Old 02-14-2013, 06:11 PM   #29
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Will the size of my ducts have to be changed?


If I am going to go where most people in my neighborhood are afraid to go meaning a smaller unit I need to:

1.) Find me the best 1.5 ton unit that is out there.

2.) Place those return and supply registers in the most optimum place.

3.) Seal up all the leaks I can find because that will make a big difference.

4.) Put more insulation in the places I can access.

5.) Trust that I have done my homework.

6.) Any input would be greatly appreciated on anything,placement of registers, what brand ac/heater unit to go with. Anything...............

7.) Any thoughts on how big the heater should be?
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Old 02-14-2013, 06:22 PM   #30
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Quote:
Originally Posted by Pawl View Post
Thanks for the compliment. I bought this house in 1986 as a fixer upper. I did everything you see in the pictures,landscape,windows,lighting,roof,skylight, solar tubes,painted it twice and on and on. I just stole all the ideas of the newer houses in the area,took off the old looking design and now it has great curb side appeal.

If I did not know how to do something I kept asking questions. Most everything is paid for because I did the work. I have some things to still do to seal my house up tighter like fireplace,more batts in the attic,front door seal,etc,.. All the things I should have done long ago.

1.) Are you changing 4 ton to 3 ton because the 4 ton needs replacing?

2.) I put a swamp cooler in here years because I could just never afford a complete AC unit, That cooler kept this house very comfortabe unless it was a humid day. We don't get humidity that often. But for $350 I used that unit for 10 years. And my electric bill did not go up much.So I am pretty certain a 1.5 ton unit will work fine. My kids are grown and gone. It is 99.5% of the time me just living here so I should be fine.
The 4 ton unit is only 6 years old but when I replaced it, I changed it out from the original unit which was also a 4 ton unit. I was always taught in the old days to change equipment like for like, or go on 400 sq ft per ton, which I've learned over the last few years is a no no.

We also originally had a gas unit and by some stupid brainstorm, I thought going heat pump would be the better way but lately I'm not sure in comparing our power bill with the neighbors gas bill. I think gas has dropped in price here over the last few years.

Anyway, I'm going back in with a 3 ton gas packaged unit.

You say you've been running a swamp cooler down there? We have also for years but my Mrs hates them and when I put the new unit up, the swamp cooler which is up there on the roof also, will be coming down for good.

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