2 a/c units - do we need 2 erv's?

15 years ago

We're still in the HVAC planning stage, a 16 seer Trane.

(2,975 sq. ft. foam insulation, unvented attic, heat load calc. recommendation 5 ton)

The installer is recommeneding 2 units. He says we will need 2 energy recovery ventilators (one per unit), plus a ventilation fan in the attic to get rid of the sweating of the unit that goes in there.

Does this sound right? Thanks!

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Comments (7)

zl700
15 years ago
One 130-180 CFM incorporated into the main HVAC unit is fine. (The air will blend in the house). If for some reason you did want two, you could go with two smaller ones in the 60-90 CFM range

Wouldn't make sense to me though to double the penetrations outside and service required.

With regards to the fan in the attic, if you are going with a ridge vent, soffit vents and my recomendation of a solar barrier, adding a fan will disrupt the designed flow and can acually raise the attic temp by short cycling the air from the ridge vent right into the fan.
emilynewhome
Original Author
15 years ago
So purchasing one ERV, incorporated into the larger a/c unit would be OK.
We are considering the Trane Fresh Effect ERV, they make a 130 cfm, 200 cfm, and a 300 cfm.
Our attic is unvented so that's why the installer recommended the fan.
Reading some of the earlier posts I see the Trane 15 seer is recommended over the 16 seer. We were considering a heat pump but installer thinks not a good idea.
He is supposed to be calling back with figures and model #.
Our earlier foray into HVAC fell through as dealer and builder had issues. This installer was reccomended by the building supervisor so we are hoping he'll work out.
Yes, the rest of the construction has gone forward, they are painting as I type!
I can't wait until we are done!
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guinnesses
15 years ago
A heat pump is never a bad idea. Sounds like your installer wants to simply install what is easiest to install.

If you like the Trane equipment, get another quote from American Standard. It's the same as Trane, but they have stricter standards for their dealers. Try to get a "Customer Care" dealer. Each customer is surveyed and they must maintain high scores to remain a "Customer Care" dealer. You can find a dealer at americanstandardair.com
energy_rater_la
15 years ago
5 tons on 2900 sq ft...wow!

I would not plan on erv until house is competed and
tested for tightness. Unless less than .25 air changes per hour is achieved, erv (fresh air/make up air) is not necessary.
Also, heat pump is the way to go.

best of luck.
zl700
15 years ago
Really an unvented attic?

When the heat and moisture travels up, where does it go, rot the roof?

If you install an exhaust fan in an unvented attic, where will the air come from that will be exhausted, every crack,light box and crevice it can from the conditioned space below?

The size of the ERV depends on not only construction type but personal preferences, such as will it be used as a kitchen odor exhaust, will it be a primary bath exhaust, and how do you intend on controlling it and how long will it operate.

Trane has the same progran as Customer care, it is just called Trane Comfort Specialist. The programs are near identical and involves training, customer commitment, maintaining a quality record.
emilynewhome
Original Author
15 years ago
Please forgive my ignorance on this subject, I've been trying to digest what I've been reading here and on HVAC Talk.

If I understand correctly, a heat pump is the way to go!

(The installer spoke of electric strips being more than enough heat. He totally lost me, as I didn't even know that a/c had heat/electric strips).

As for the fan, I'm not sure if the installer intends to vent it to the outside, but then I don't understand the whole condensation thing since we have a foam insulated, unvented attic.

The ERV unit is my idea, as previous posters and other sites suggest bringing fresh air in, especially in a tight house. (Ours is closed cell in walls and open cell in unvented attic).

I don't care one way or another about the Trane Clean Effects especially as it is extra cost.

This is the third installer DH and I've talked to, and our builder pretty much has decided this is who he plans to use.

From what I'd read and researched I initialy asked for a single unit 16 seer Trane heat pump with ERV. (Thanks to the posters who pointed out the need for 2 units especially in the south).

I should also mention that we will be paying $3,500 difference for metal duct versus flexduct. Our builder has alloted $11,000 total for HVAC.

Please, please help me! What should I be asking in a HVAC system for our home. It is a one story, 2975 sq.ft. S.W. Louisiana, heat load recommended a 5 ton unit.

Thank you all so much!
msm859
15 years ago
i have an unvented attic with sprayed foam insulation with one of the air handlers in the attic. have 2 trane XL 19i units. not worried about moisture issues. if you are willing to pay +$3500 for metal duct why not go ahead with the most efficient ac unit

2 a/c units - do we need 2 erv's?

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zl700

emilynewhome
Original Author

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2 a/c units - do we need 2 erv's?

Comments (7)

zl700

emilynewhomeOriginal Author

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