system sizing help...new construction

[robdidomenico]

hello all,

first of all, thanks for the great info on this site...i have learned alot about HVAC, but I think it is getting to be a problem...

building a new house (technically a renovation) with 2900 sqft above ground, and 1400 sf basement in northern NJ (15 min outside NYC).

Here are the stats.

size 53x30, 53 foot walls on north/south axis. half of the south wall, first floor will have a covered patio. 38 feet of the north wall has a front porch.

1400 sf full basement...unfinished for now, but will probably do it after i get a C.O. will insulate with r-10 fire rated foam (thermax) and finish w/drywall.

1400 sf first floor - average amount of low-e andersen 200 windows. r13 2x4 walls with r5 foam sheathing and vinyl siding. open floor plan, 8ft ceilings throughout. 9' x 14' 2 story entry foyer.

1500 sf second floor, 4 bed 2 bath, laundry room. r30 attic insulation (for now), same walls and windows as first floor. r19 in between 1st and 2nd floors for "soundproofing".

HVAC guy wants to do 2 systems - all new everything.
1. 90+ gas furnace (90000 BTU) and 4 ton AC (14 or 16 SEER) for 1st floor and eventually the basement. ductwork in the basement, coming up to the first floor, wrapped with r6.

2. in the attic, 80% gas furnace (70000 BTU), and 3 ton AC for the 2nd floor. ductwork will be in the attic, but connected to the downstairs, wrapped with r6. does not want to do 90+ in the attic b/c of the condensate (which i have read is a bad idea, but there are ways around it.)

from everything i have read, this seems like overkill. I really want to avoid this and am concerned about energy use...at least I will make sure to get 2 stage or modulating equipment. I even ran the demo of right J myself (Washington DC is close enough), and got a heat loss of 75000 BTU (w/o basement) and total gain of 55000 BTU (45K sensible + 10K latent) for the AC (again, w/o basement).

He installs Rheem, Amana, Goodman, and Trane. I like the Rheem stuff, really want the RGFD mod for the downstairs, but that will have to be worked out between me and my builder. As you can see, I need alot of help. I only want to build once, and am putting down roots for the next 20+ years.

Let's work on sizing first, then equipment choices. I am pretty much stuck with 2 units. He does not seem to want to bend on this and has already put in registers and ductwork. So I really need some advice regarding equipment sizing. If there is any other info you need please let me know...and thank you in advance for any info you can provide.

[dan sw fl]

Spray foam insulation required for attic ceiling.

I didn't see where you made provisions for Outside Air.

[beenthere]

Basements take very little to heat or cool them.

Did you show your contractor the load calc you did.

7 tons is probably gong to make your house humid in the summer. And cause you to have to set the thermostats to less then 70 to be comfortable.

[Rdy2Zone]

You state that the ductwork and registers have already been installed. You may want to confirm that these are properly sized for the 90K-BTU furnace / 4Ton AC and the 70K-BTU furnace / 3Ton AC.

If you post the size of the main supply and return trunks, one of the pros here will most likely tell you if they are undersized (as they often are for some reason).

Talk to your contractor about zoning the two systems further with separate thermostats per room, motorized dampers and a zoning control panel.
This technology has been around for a while now and works well.

Zoning should meet your requirement of further energy savings by requiring much smaller HVAC systems and only conditioning areas that are occupied.

The additional cost of zoning could be offset by the reduced cost for smaller HVAC systems and lower energy cost.

[teddy bear]

Air tight homes need fresh air ventilation. Homes with low cooling loads and basement need supplemental dehumidification. Investigate the ventilating dehumidifier for indoor air quality and ideal comfort. Check out the the Ultra-Aire whole house system. It is the best and was the pioneer. Regards TB

[robdidomenico]

i think i was not clear about the construction...it is NOT foam insulation.

r13 fiberglass batts in the wall cavity, r5 foam sheathing OUTSIDE for a thermal break and extra overall R-value for the wall. r30 fiberglass in the attic floor.

ducts, 2nd furnace in the attic will be in unconditioned space.

i went up there this morning and took pics. some of the duct work is in place. i saw a sticker on one of them that says "oval stackhead 6x12 7" ". made by standex # 5037-762.

for the 1400 sf 1st floor there are 10 registers - 2 for each large room, one for each small room.

for the 1500 2nd floor they are in the ceiling - one per room, 2 in the master, for a total of 9. One large return as well - looks like 16 x 28, or 16x24.

Hopefully that clears things up and hopefully someone can address my original concern of oversizing the furnace and AC. thanks again everyone for your time...

[beenthere]

7 tons still sounds too much.

Do your own load calc. Use HVAC Calc (http://hvaccomputer.com/talkref.asp)
And you will see.

[dan sw fl]

Hopefully that clears things up and hopefully

_someone_ can address my original concern of oversizing the furnace and AC.

5 tons neeeded, 7 tons spec'd

160,000 btu/hr spec'd _ < 1/2 75,000 needed.

SOME ONE_ Would Be THE OWNER in this case! !! !!!

State what you will accept.

[BaldLoonie]

Sounds nuts to me. 160K heat and 7 tons for 2900 sq ft above ground? Here where we get to 95 & humid in the summer and -10 occasionally in the winter we'd probably throw a 100K 95% and 3.5 ton cooling at it. And that's a 20 year old home. New construction could be less.

No reason you can't go 2 systems, just the right size. As you found, 75K loss may not be far off. If you want a Mod, RGFE-06 downstairs, maybe a 2 ton A/C since cold air will fall from upstairs and heat that infiltrates downstairs will rise. Upstairs how about a RGPR-05 with a 3 ton A/C. Many think smaller A/C up but I don't buy that. For much of the summer you could turn off the downstairs and cool the whole house with the upstairs machine.

Even if not foamed, might want to consider a whole house dehumidifier with intake capability. Helps to have fresh air brought in with the off-gassing of the new construction besides keeping humidity down.

[robdidomenico]

not that easy to "man up" b/c this is my first time doing this and do not want to screw it up...to complicate matters, it is me vs. the whole lineup. HVAC guy, builder (friend of the family), my dad (just listen to what they say, they do this all the time!).

I just want good info and a little confidence in my position. So I did what any normal person would do: consult random "experts" on the internet!

to be fair, the HVAC guy said his load calc came to 2.5 ton for the second floor. wants to add 0.5 to be safe. it's the downstairs that seems to be overkill.

i am planning on fresh air intake (dad says - what do you need that for, just open the window! not easy dealing with old school guys...).

does the ducting seem adequate? have not heard any comments so I guess it is not bad...is the one large return in the second floor ceiling enough? are there enough supply runs?
thanks again...

[beenthere]

Its not the number of supply runs that counts.
As much as it is the size of them.

[udarrell]

Building a new house (technically a renovation) with 2900 sqft above ground, and 1400 sf basement in northern NJ (15 min outside NYC)

Initially I missed your post.
Only 2900-sf above ground in a low A/C load climate.

Heating should be your major energy consumer in that climate, not cooling.


1400-sf first floor - average amount of low-e andersen 200 windows. r13 2x4 walls with r5 foam sheathing and vinyl siding. open floor plan, 8ft ceilings throughout. 9' x 14' 2 story entry foyer.
Wow, how many ton for a mere 1400-sf first floor with a conditioned area above & below it.

Here in SW WI, I have a 1937 farm home with a lot of old windows & I cool the 850-sf first floor with a mere 6,000-btuh Half-Ton Room A/C. I use a floor fan to circulate the air through the rooms & back to the A/C. It handles the load perfectly even at 104-F Heat Index.

A 2-ton ought to cool your first floor, if the basement is below ground level it won't take much to cool it.

A manual J load calc should be done for each room & a manual D for duct system sizing.

I would want 400-cfm per-ton of cooling on each system.

System & Duct sizing overview:
http://www.udarrell.com/sizing_ac_duct.htm

[robdidomenico]

thanks udarrell for the info... great site too.

i posted the size of the ducts earlier...assuming all the runs use the same, is it the right size?

[udarrell]

thanks udarrell for the info... great site too.

i posted the size of the ducts earlier...assuming all the runs use the same, is it the right size?

I don't see the diameter of the branch-runs, however, I want you to use the info provided on the linked site & use a calculator & figure out if the duct system is sized right.

I'd Print the content areas U need, & circle relevant info so U can tell whether U have a problem to be remedied by a Tech PRO.

Beenthere told you to have a manual J load calc done for each room, then using Manual D the duct system is to be sized to deliver the correct amount of airflow to each room.

Dampers ought to have been installed where the branch-runs take-off from the main-run to better balance airflow to the rooms.

I only provide the information so equipment owner's will be enabled to figure out if they need to call a competent contractor to remedy the revealed problems. Always, contact an HVAC PRO to do the work!

For efficient operation a proper sequence should be followed, the building envelope, equipment sizing & airflow are major issues most often in need of addressing upfront.

To get the most cost-effective-payback, I'd contact an HVAC contractor that focuses on reducing your home or coml building's energy usage. - Darrell

[robdidomenico]

Lots of clarification now.

he calculated 2.5 ton 1st floor and 2.5 ton second. ductwork will provide 400 cfm/ton. TXV's on both, will use 3 ton unit for both with the 2.5 for airflow. also, I may finish the basement down the road so it will be ready for that. both systems will be certified matched.

16x24 return for each system, one upstairs and one downstairs. (opening, that is, the diameter of the hole in it looks like 12"...could be wrong b/c i forgot to ask). He also put in room return in the master suite.

does this sound better?

so now it is on to equipment...Rheem, Goodman, or Amana.

I like rheem better, but my builder usually has him install goodman. We'll see what the price differences are...either way I feel a little better about the install.

any recs for matched systems for rheem or goodman? 90+ downstairs (basement) , 80 upstairs (attic).

tax credit is not an issue b/c i will probably get it for increased insulation. i don't want to pay alot more for 0.5 SEER, so it is not such an issue to get to 16. From what I understand (and that ain't much), EER matters more.

thanks for sticking with me...

[jerryd_2008]

...

1400 sf full basement...unfinished for now, but will probably do it after i get a C.O. will insulate with r-10 fire rated foam (thermax) and finish w/drywall.

1400 sf first floor - average amount of low-e andersen 200 windows. r13 2x4 walls with r5 foam sheathing and vinyl siding. open floor plan, 8ft ceilings throughout. 9' x 14' 2 story entry foyer.

1500 sf second floor, 4 bed 2 bath, laundry room. r30 attic insulation (for now), same walls and windows as first floor. r19 in between 1st and 2nd floors for "soundproofing".

...

Sounds like you have 2 houses: 1) A 1500 sqft on top with good roof and wall insulation and good windows and 2) a 1400 sqft house with a basement that is well insulated with really, really, really great roof insulation (the floor above plus the roof above that). You want (need) 2 systems due to construction. Ask yourself, what system would you put in each if they were rental houses. As I recall Northern New Jersey (really the Shore 40 miles south of NY) it isn't too cold and not too hot. Really - 7 tons total!!!!!! IMO (as a HO) I would look very, very hard at any contractor that proposed more than two 2 ton systems (do the Manual J of course). No?:angel:

[pd07]

I would go with the Rheem products. Also 90+ in attic, I have installed many Rheem/Ruud 90+ in attics a little heat tape and insulation around condensate lines and trap, no problems. These installs are in southeast Pennsylvania.

[robdidomenico]

I want the rheem stuff, but we will see on saturday when i meet with the builder. Price is obviously a factor...

Question: Is there any major difference between Amana and Goodman equipment? I understand the installation is more important, but I still want to know which, if any, is built better.

thanks...It is nice to see so many different pros chiming in on this...

[dan sw fl]

i think i was not clear about the construction...it is NOT foam insulation.

... r30 fiberglass in the attic floor.

address my original concern of oversizing the furnace and AC. ...

Hopefully, it is clear the the attic insulation is far from optimum which
results in system oversizing and underperformance.