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Old 08-08-2011, 10:39 PM   #1
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New home. Doing HVAC myself, but making sure my builder is right.


Hello,

I am in the process of finalizing plans for a new home with a builder and I want to make sure everything is sizing up with the HVAC.

I used to work for my father who is an HVAC contractor. I used to install whole systems, but I never engineered or sized them. I have some idea of sizing, but I want to make sure everything is right with the builder's specs.

This is being built in the northern suburbs of chicago, and there is the potental of huge swings in temperature. Last winter it got I think colder than -20F and it recently got to 95+ this summer.

Since I can get units for cheap (I can use my dad's account), I am definitly going to get two stage variable speed 95% heat and two stage 16 or 18 SEER condenser units.

I am also putting one unit upstairs and one unit downstairs.
I also going to have the outside walls built with 2x6s instead of 2x4 and putting in thicker insulation.
I will be installing an attic fan and installing additional insulation in the attic.

I bought the plans online and here is the link to the house design and floor plans. I am not sticking to this exactly, there are a few minor changes, but nothing drastic.
http://www.houseplans.net/floorplans/06400029/
I am also having a full basement (instead of the crawl space) which I will finish a few years down the road and I will be insulating it.
both floors are going to be 9 foot ceilings.

I was told I should have
Upstairs
2 tons of cooling
46,000BTU of heat

Downstairs
2 tons of cooling
69,000BTU of heat

Does this sound right?

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Old 08-08-2011, 11:10 PM   #2
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New home. Doing HVAC myself, but making sure my builder is right.


You have a great opportunity to do things right.Do your manuel"J" and manuel "D"
Spend the extra for top notch windows and doors.
Remember that a single return can be ok for the equipment but terrible for house comfort.
You are going to need a humidifier,get a good one.
When you xcharge the unit use subcooling or superheat to do it right.
It is more important to have enough room around the indoor unit than it is to have a wall around it.

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Old 08-08-2011, 11:17 PM   #3
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New home. Doing HVAC myself, but making sure my builder is right.


I have never done a manual J or D.

I will have Returns in every room (except bathrooms and closets). I know how to calculate superheat and subcooling.

I will be using humidifers.

I just never done sizing for a house before.
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Old 08-09-2011, 03:05 AM   #4
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New home. Doing HVAC myself, but making sure my builder is right.


I never asked if you had ever done a manuel"J" or a manuel "D".
Doing these two calculations is the single "must do.
If you pull a size out of your back pocket will open up the chance that you put something too big.If your unit is too big,it costs you more than it should cost you extra every time it comes on for the next twenty years.Too small and you will never get it comfortable in the house.
Even if you have to pay for these calculations,you'll end up savings thousands over the course of its life time.
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Old 08-09-2011, 07:16 AM   #5
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New home. Doing HVAC myself, but making sure my builder is right.


Can't give an answer to that question on line , you have to figure all that out. Why not get Pop involved and have him do the calcs and ductwork design with you I'm sure his information will be on the money.
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Old 08-09-2011, 05:43 PM   #6
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New home. Doing HVAC myself, but making sure my builder is right.


Spray foam the attic, then you won't need an attic fan.

2 tons sounds a bit much for the small second floor. 528 sq ft a ton on new construction is over sizing. But you won't find a 2 stage in a 1.5 ton size.
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Old 08-09-2011, 07:46 PM   #7
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New home. Doing HVAC myself, but making sure my builder is right.


wouldn't this doing it yourself heat and air void any warranty on the components? or maybe this has already been considered?
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Old 08-09-2011, 07:58 PM   #8
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New home. Doing HVAC myself, but making sure my builder is right.


Quote:
Originally Posted by Aphid View Post
wouldn't this doing it yourself heat and air void any warranty on the components? or maybe this has already been considered?

My guess is he will have his dad lie and say he installed them.
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Old 08-09-2011, 08:06 PM   #9
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New home. Doing HVAC myself, but making sure my builder is right.


ah ok
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Old 08-09-2011, 11:27 PM   #10
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New home. Doing HVAC myself, but making sure my builder is right.


i agree with REP, it is much more convenient to have the ENTIRE a/c system planned out and sized as close to perfection as it can get. it will save u headaches in the future and you wont regret seeing ur a/c unit still working in the 15-20 yrs to come

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