Help with my new home HVAC sizing

[Cwatts15]

We are building a 2900sqft home and I have been getting bids for my HVAC. My problem is that we are getting different opinions on the unit tonnage needed. We are using foam in walls, with zip board system and blown in cellulose in the ceiling and radiant barrier. We live in Tulsa, OK. Our house faces northwest with 4 windows in that direction-1 is under porch. The rear of house is southwestare and all the windows (12) are all under a lg covered porch. 2 window face northeast, and 2 sml are south facing. We requested 2 units because we like to sleep cold with good air movement and thought a sml unit for our side approx 900sqft and a larger one for the reaming 2000sqft. We also have considered just 1 unit and getting a mini-split for our bedroom. We have mostly all 9ft ceilings, but have 10ft in center in living room and kitchen. I would appreciate any suggestions because I don't know who to believe. I also want an ERV air exchanger. Thx for any advice!

[jtrammel]

An ACCA manual j or equivalent computer program (ie wrightsoft) is the only way to get the proper heat gain/loss calculation of a house. Anything else is a guess. As for erv, I would reccomend a whole house dehumidifier with outdoor air instead. In a new tight house you should be able to easily get 800-1000 sqft per ton or better. I would also require a blower door and duct blaster test be performed at completion to certify the tightness of the structure and duct system.

[HVAC/Stud]

jtrammel is correct!
I'd add a manual d and s.
I go with a mini-spit for bedroom.
Don't let the builder drive the train, its your house and you have one chance to get it right. Builders will put a 5 cent HVAC system on a $500,000 house.

STUD

[dan sw fl]

We are building a 2900 sq ft home and I have been getting bids for my HVAC.
My problem is that we are getting different opinions on the unit tonnage needed.
We are using foam in walls, with zip board system and blown in cellulose in the ceiling and radiant barrier.
We live in Tulsa, OK.

Our house faces northwest with 4 windows in that direction-1 is under porch.
The rear of house is southwestare and all the windows (12) are all under a lg covered porch. 2 window face northeast, and 2 sml are south facing.

We requested 2 units because we like to sleep cold with good air movement and thought a sml unit for our side approx 900 sqft
and a larger one for the remaining 2000 sqft.

We also have considered just 1 unit and getting a mini-split for our bedroom.
We have mostly all 9ft ceilings, but have 10ft in center in living room and kitchen.
I would appreciate any suggestions because I don't know who to believe.
I also want an ERV air exchanger. Thx for any advice!

You will have as many opinions + 2 as the number of people you ask.

Ceiling R- ___ ?
Walls R- ___?
Infiltration __ < 0.3 ACH ?

Design should include mechanical room so equipment and ducts are in conditioned space.

Window U-value < 0.4, SHGC < 0.35, VT > 0.60
See Marvin Windows or other.

http://www.climate-zone.com/climate/...klahoma/tulsa/

Dual Fuel = Heat Pump + Natural Gas Furnace
http://www.eia.gov/forecasts/steo/ta...ableNumber=16#

http://www.eia.gov/naturalgas/

Electric rate = $0._ _ / kw
Natural Gas is likely in the range of $0.90 / therm

[dan sw fl]

$0.84 / therm in OK
http://www.eia.gov/dnav/ng/ng_pri_su...PRS_DMcf_m.htm

[BaldLoonie]

Too many oversize a tight, foamed house. I agree on the bedroom mini. Probably only need a ton or so. Then whatever the 2000 sq ft needs, maybe a 2.5 ton.

www.energywisestructures.com

[dan sw fl]

http://www.energy.ca.gov/efficiency/...protocols.html

[Cwatts15]

Thx for so many replies. We currently live on site where we are building. We built a metal shop and made a sml apartment in it to live till home built. We spray foamed the walls and blew the ceilings in. The one thing I have noticed is the stale air over this last winter. Headaches, sinus problems and cough. I just thought it was the season until we spent time away and no h/a's. Come back h/a, stuffy nose etc. I did not know about the air exchange needed for spray foam insulation. I have read more about it and understand kind of what I need, but some of the HVAC I talked to for bids don't even mention anything about fresh air, just like the guy that installed the HVAC for our apartment. 3 bids- all very different, 1: 2ton & 3ton 80% 13seer Lennox- gas unit with optional ERV, 2: 2ton & 5ton 93% 13seer Armstrong with option fresh air damper. 3: 5ton & mini-split Armstrong. I don't have a program to calculate what I need.
Now do we need that much tonnage? We are doing all energy star windows too, and open cell foam in walls (2x4)

[jtrammel]

All look oversized to me. Is the builder bringing in the subs or are you suppose to be choosing your hvac sub. I would find a good contractor who will do the proper calculations and go over all your options with you.

[udarrell]

It appears U have a well insulated home with too little air infiltration; you'll need a ventilation system.

I can't imagine anyone thinking U need 7-Tons of cooling; Tulsa is similar to OKC; maybe a little more humidity but OKC is has low humidity.
The load-calc below will show you the 'difference' in grains of moisture between outdoors & the indoors room temp-design you select. (I'd never go below 75F; on real hot days U should be comfortable at 76 to 78F & 50% or less humidity.)

Since U should know the input value numbers; here is an on-line Whole House load-calc for both cooling & heating.
You have to print the results because U can't save the results.

I would use .4 Air Changes per Hour (ACH), put the CFM it calculates on the line above, where it estimates the added air you need.

Print the instructions & steady & follow them; play with it until you are sure you're doing everything right.

Tell us what load-calcs you get; I think you'll be very surprised!
Whole House Load-Calc

[BadgerBoiler MN]

An ACCA manual j or equivalent computer program (ie wrightsoft) is the only way to get the proper heat gain/loss calculation of a house. Anything else is a guess. As for erv, I would reccomend a whole house dehumidifier with outdoor air instead. In a new tight house you should be able to easily get 800-1000 sqft per ton or better. I would also require a blower door and duct blaster test be performed at completion to certify the tightness of the structure and duct system.

This is exactly right and the place in which every properly designed HVAC system starts. Without an ACCA Manual 'J' you simply don't know what you are doing, and neither does you contractor. Most homeowners/builders should hire licensed trades directly, showing them a set of plans and asking them for a sample heat load or Manual 'D' drawing. The heating contractors that can produce a Manual 'J' will be few and far between.

We specialize in radiant heating systems using Wrightsoft but have been using other modules 'D', 'N' and High Velocity to cover our subs who would rather guess than do the math.

It doesn't matter where the designer is, as Manual 'J' using your local climate to come to the right loads. Once you have the loads you can spec the heating and cooling equipment, ventilation and duct sizing.

[dan sw fl]

Thx for so many replies. We currently live on site where we are building.

1 .I don't have a program to calculate what I need.
2. Now do we need that much tonnage?

We are doing all energy star windows too, and open cell foam in walls (2x4)

1. No detailed response to post # 4 so a Meaningful Manual J8 cannot be provided.
2. MIGHT Be ~ 3 tons TOTAL

[dan sw fl]

It appears U have a well insulated home with too little air infiltration; you'll need a ventilation system.

I can't imagine anyone thinking U need 7-Tons of cooling; Tulsa is similar to OKC; maybe a little more humidity but OKC is has low humidity.
The load-calc below will show you the 'difference' in grains of moisture between outdoors & the indoors room temp-design you select. (I'd never go below 75F; on real hot days U should be comfortable at 76 to 78F & 50% or less humidity.)

Since U should know the input value numbers; here is an on-line Whole House load-calc for both cooling & heating.
You have to print the results because U can't save the results.

I would use .4 Air Changes per Hour (ACH), put the CFM it calculates on the line above, where it estimates the added air you need.

Print the instructions & steady & follow them; play with it until you are sure you're doing everything right.

Tell us what load-calcs you get; I think you'll be very surprised!
Whole House Load-Calc

I understand ACH=
_____TIGHT __: 0.15
SEMI-TIGHT __: 0.26
_ AVERAGE __: 0.39
SEMI-Loose __: 0.61
___ Loose ___: 0.82

based on my use of Manual J8 abridged.

Some residences with foam products ought to be < ~0.2

[udarrell]

I understand ACH=
_____TIGHT __: 0.15
SEMI-TIGHT __: 0.26
_ AVERAGE __: 0.39
SEMI-Loose __: 0.61
___ Loose ___: 0.82

based on my use of Manual J8 abridged.

Some residences with foam products ought to be < ~0.2

Right Dan; I was just using .4 ACH for his situation because his home needs to be above the code minimum home air-changes of 0.35 ACH, when it is properly ventilated.

Of course, the proper way is to do the blower door test & use the actual lower ACH number so the load-calc would estimate the needed makeup air...then he should use 0.2 or less ACH.

[Cwatts15]

Ok I tried to figure out the Manual J. This doesn't make sense to me. Did I do this right?

[dan sw fl]

LOOKS like you put in about 900 sq feet of window which seems to be nearly 3 X too much.

Ceiling is ok.
Walls are not enough.

[dan sw fl]

A GUESSED 12-Minute analysis Version of _Whole House Load Calculator_ is attached
simply
knowing 2,900 Square Feet total and walls are foamed.
Ceiling R-38
_Walls R-18
Total Window Area 380 Square Feet

I would say windows may be ~6,000 BTU/Hr too much for Sensible Load (Heat Gain) if you actually have SHGC < 0.36.

However, I don't even know how many windows, total glass area, exact orientation, U-value nor SHGC.

[Cwatts15]

I tried to open you calc, but it says I don't have permission. I tried to redo the calculations. See if this is better. I do have a lot of windows on our southeast wall, and all of them are under a cover patio. I really appreciate all your help.

[Cwatts15]

Ok, I was able to open it, and it is really different from mine. So bottom line, what does calc recommend for HVAC size and ventilation needs. I know I am stupid when it comes to understanding all this.

[mark beiser]

3 bids- all very different, 1: 2ton & 3ton 80% 13seer Lennox- gas unit with optional ERV, 2: 2ton & 5ton 93% 13seer Armstrong with option fresh air damper. 3: 5ton & mini-split Armstrong.

Pure speculation without doing a load calculation, but I think it would probably be best if you toss all 3 of those bids in the trash.
#1 and 3 are the kind of sizing you would see in a stick built house with a questionable thermal envelope in North Texas.
#2 is just ridiculous.

In a tight, well insulated 2900 sq ft house, unless you have some really big unshaded west windows,I'd be skeptical of anything that came out to more than 3 tons + ERV for the main part of the house, and a minisplit for the master bedroom.
If you do have really big unshaded west facing windows, a conventional system will always struggle to evenly heat and cool the home due to its load diversity.
Applications where there is high load diversity is where systems like a Daikin VRVIII-S really shine.