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1 Answer

Supply ventilation via ducted mini-split

I notice that some of the ducted mini-split models have provisions for a fresh air port. Would using this be a reasonable way to implement a supply-type ventilation system? They say it should be limited to 10% of the flow rate. If that doesn't satisfy the required ventilation flow rate, how best to supplement it?

Asked By Reid Baldwin | Sep 4 15
1 Answer

Add rigid foam during re-roof

Our home on a barrier island 30 miles south of Wilmington, NC (close to NC/SC border) needs to have its shingle roof replaced. We’re planning on going to a standing seam metal roof.

If we know we want to eventually condition the attic, should we add rigid foam on top of our sheathing during the re-roof? Or spray foam the attic later?

If rigid foam makes sense now, what is the recommended type and thickness for this application?

Other house details
Climate zone: 3 Coastal
Built in 1947 (survived Hurricane Hazel!)

Asked By Robb Czyzewski | Sep 4 15
10 Answers

Is this a risky wall assembly?

I am in the process of finalizing plans for a 2 story 2385 square foot home in Zone 6 WI 44.3353° N, 88.6389° W. I have been trying to get in the pretty goodish house category as far as insulation levels and while not where I'd like them to be am currently sitting with the following setup due to budget.

R10 EPS below slab insulation
R10 EPS exterior Foundation walls (will finish off basement later and can add interior insluation)
2x6 R20 damp spray cellulose with R7.5 Atlas Thermalstar LCI-SS EPS insulated sheathing
R55 blown cellulose attic insulation

Asked By Jeremy Coenen | Sep 3 15
2 Answers

How stupid can I be?

My firm just spent hundreds for a load calculation program that takes in fenestration, wall and roof loads, lighting and other internal gains, outdoor air for ventilation, location, exposures, etc. and now I find out I could have used 1000 square feet per ton! It even divides nice in base ten, by moving a few decimal places.

But seriously, the blog regarding a rule of thumb of t ton per 1000 square feet is the most idiotic, misleading, and oversimplifying way to create a cooling load that I have heard to date. ASHRAE gives the standard of care as computer analysis and that's what we do.

Asked By Warren Worth | Sep 4 15
15 Answers

Water supply line routing

I'm building a house in Western Montana at 3500 ft, climate is not bad other than a couple week cold snap every year, though that may change. Had a couple of brain farts during the design in regards to water lines on exterior walls. It is a slab with radiant heat, so can't go in the floor.

The specs:
Shed roof, unvented with 4" ISO on the roof under rubber membrane.
Planning on R40 batts then drywall with very few holes other than some junction boxes for lights.

Walls are covered in 2" of ISO with 3/4 airspace behind siding.
Planning on batts or something in the R21 range.

Asked By Stan Smith | Sep 3 15
4 Answers

Cost comparision between conditioned and vented crawlspace

I am designing and will build a house for my mother which will be a ranch on a crawlspace. It will be in Vancouver, WA (near Portland, OR) and as one study showed, a vented crawlspace here isn't all that bad.
After seeing several homes whose underfloor insulation hasn't held up well over the years, (batt fiberglass tied up between TJIs), I'm thinking a condition crawl would be more durable.

Asked By Mark Walker | Sep 4 15
19 Answers

Concerns about backdrafting and makeup air

We're in the process of air sealing a mid-Atlantic house built in the mid-80s. (Today is a humid 94 degrees and in the winter we go below freezing.) We had low CFM-rated (OKNA-brand) windows installed recently. After we seal the rim joists and the attic, I am concerned about what make up air and backdraft situation will be. We will be installing a 300 CFM range hood soon, too. Our water heater was just replaced with a power vented model, and we expect to replace the furnace very soon. We do have a wood burning fireplace.

Asked By Forum User | Sep 3 15
5 Answers

New 20+ SEER Variable Carrier heat pump w/ Greenspeed Intelligence system creating moisture & performance problems in the crawl

I had to replace 2 -13 SEER HVAC split systems in my house about 2 years ago do to some Sandy storm damage. One split system was a 90% gas furnace with a 3 ton 13 SEER AC and the other was a 2 ton 13 SEER heat pump.

Asked By Bruce Howe | Sep 2 15
6 Answers

Ducted mini-split serving multiple floors

I am attempting to break my house design into zones such that I can use one mini-split for each zone. I am having trouble simultaneously satisfying two pieces of advice from this forum. In "Rules of Thumb for Ductless Minisplits," Martin says that one ductless head can serve a maximum of about 1100 square feet. That is based on distribution, not capacity. I realize that it is a rule of thumb that might not apply to a super-open floorplan, but if I violate that rule, I should have some justification.

Asked By Reid Baldwin | Sep 2 15
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