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Looking into dehumidifier - what are the considerations?

Posted by pbx2 (My Page) on
Thu, Oct 11, 12 at 15:20

We are looking into dehumidifier for our new build.
House will be certified & blown door door tested tight.

* ~2950 sf.
* 1.5 stories.
* MidAtlantic region
* Heat Pump

Opening window will be our 'air exchange'.
Looking to low humidity to provide comfort & energy efficiency.

What should be some considerations? Thoughts please.


Follow-Up Postings:

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RE: Looking into dehumidifier - what are the considerations?

** Adding **
No Basement
Conditioned crawlspace

Looking for whole house dehumidifier.


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RE: Looking into dehumidifier - what are the considerations?

Your HP will qualify as a 'whole-house dehumidifier'. Though it will do a better job of it if you get a variable (not variOUS) speed blower, or additionally a 2-stage unit.


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RE: Looking into dehumidifier - what are the considerations?

@weedmeister - it's a Trane XR16 heat pump multistage (not sure 2stage or variable).

Can you expand on why it will help as a dehumidifier please?


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RE: Looking into dehumidifier - what are the considerations?

A good, modern versatile cooling system can be set to a low blower speed and regulate the cooling coils to a low temp to maximize dehumidification. It will not, however, substitute for a dehumidifier if your climate is very humid and you have lots of time with no or little heat or cooling required.


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RE: Looking into dehumidifier - what are the considerations?

Any AC unit (HP or normal) acts as a dehumidifier pretty much by definition.

That looks like a 2-stage HP. Ask for the variable speed blower (you're probably getting it by default). Ask for a thermostat that has 'dehumidify on demand'. This lets you set a humidity level as well as a temperature setpoint. In this mode the fan runs low and the HP runs in 1st stage so as to remove humidity without driving down the temperature too much.


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RE: Looking into dehumidifier - what are the considerations?

There's another site, where questions can be answered only by people who've been pre-screened to confirm they're HVAC pros. There's one regular participant there who seems to take a particular interest in dehumidifiers, put that into the subject field of a post and you'll be sure to get a lot of expert help

(one of the regulars here, energy rater, is also a regular over there)

Click on the link below:

Here is a link that might be useful: HVAC Forum


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RE: Looking into dehumidifier - what are the considerations?

Ever air conditioning cooling system is ALSO a dehumidification system.
It is extrinsic to the cooling design.

A cold surface cools the air and condenses out water vapor.

Some newer systems have the option of a humidity set point as an input, most (new or old) do not.

When they cool the air water, vapor condenses out and is drained away.

Low humidity is counterproductive during heating season.


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RE: Looking into dehumidifier - what are the considerations?

If I were building your house, I would seriously consider building the HVAC system without the dehumidifier, but making provisions for adding it later. That means setting aside the space and make sure that the duct configuration will accommodate it. You can judge after a year or two whether you need it and add it or not.

In my hot, humid climate, there are several weeks in the spring and fall when I need minimal cooling, but it is very humid. Even though the AC can be biased to remove moisture effectively, it gets too cool under some conditions so I run the dehumidifier and cooling at the same time, mostly at night.

Mid Atlantic is not as humid as the Gulf of Mexico coast so you might not want to spend the coin to bring down the humidity a couple of days a year if that is what it amounts to in your situation.


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RE: Looking into dehumidifier - what are the considerations?

@ionized - thank you for the thoughtful comments.

U are spot on with your assessment of our "50/50" weather/temp/humidity.

However, because our house is one of these newer tight houses, we still have to determine if steam from cooking & showers can somehow be minimized with our new Trane XR16 2-stage + variable speed blowers.

So "saving space" - may be a better idea than pre-emptively installing a whole house dehumidifier that can do upto 3K sf like a UltraAire or Santa Fe costing upwards to ~$2K.


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RE: Looking into dehumidifier - what are the considerations?

I have the Carrier Infinity varible speed furances and 2-stage ACs. During the summer I have hit humidity levels of 36%. The usual range is in the 40s.

In my opinion you are better served putting the money toward a good 2-stage AC rather than a whole house dehumifier. The Carrier Infinity equipment is very good at dehumidifying. The Trane XL20i would probably do a better job than the XL16 since it has two compressors.


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RE: Looking into dehumidifier - what are the considerations?

Posted by mike_home (My Page) on Mon, Oct 15, 12 at 12:53
I have the Carrier Infinity varible speed furances and 2-stage ACs. During the summer I have hit humidity levels of 36%. The usual range is in the 40s.
In my opinion you are better served putting the money toward a good 2-stage AC rather than a whole house dehumifier. The Carrier Infinity equipment is very good at dehumidifying. The Trane XL20i would probably do a better job than the XL16 since it has two compressors.

@mike_home - good experiences I see with your AC & variable blowers. Exactly what I wanted to hear!

& What I am after...except with a XR16 Heat Pump which is 2 stage & exchange handler with variable blowers.

Here is a link that might be useful: Trane XR16


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RE: Looking into dehumidifier - what are the considerations?

Should be this XR16 Heat Pump

& the Hyperion XL Variable Speed Air handler:
http://www.trane.com/Residential/Products/Air-Handlers/Hyperion-XL-Air-Handlers

Here is a link that might be useful: Should be this XR16 Heat Pump


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RE: Looking into dehumidifier - what are the considerations?

If you have an enclose crawlspace that is not vented to the outdoors, you might start with a freestanding dehumidifier in it. That may be enough to keep your crawl and first floor dry. You can always add a whole house dehumidifier to the HVAC system if you want dehumidified fresh air and good humidity control in the living space.

Santa-Fe units are a good choice for the crawlspace. Ultra-aire units are great whole house dehumidifiers if you want fresh air ventilation as well.

Here is a link that might be useful: santa fe dehumidifiers


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RE: Looking into dehumidifier - what are the considerations?

A 2-stage heat pump should also provide good humidity control. The key pieces are a low stage which is small compared to the heat load, and a good cool to dehumidify thermostat.


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RE: Looking into dehumidifier - what are the considerations?

@ Dry_Dog: would we still need a crawlspace dehumidifier if it's a conditioned & sealed crawl space?


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RE: Looking into dehumidifier - what are the considerations?

Posted by mike_home (My Page) on
Mon, Oct 15, 12 at 14:23

A 2-stage heat pump should also provide good humidity control. The key pieces are a low stage which is small compared to the heat load, and a good cool to dehumidify thermostat.

I hope you are 100% on the money mike_home!

Any recommendation for t-stats? What about the NEST T-stat below? I'm not an Apple fanboy or anything but this seems to be getting a lot of good PR.

Here is a link that might be useful: NEST Thermostat


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RE: Looking into dehumidifier - what are the considerations?

For a nice Wi Fi stat with more controllability than the nest, check out Eco Bee.
www.ecobee.com

There is a phone app that basically allows you to use your phone like a remote control, both when away and at home.

All software is pushed from their server free of charge.

It even pulls the outdoor temperature from your location, so an outdoor temp sensor isn't needed.

Feeling a bit chilly at 2 am?.... No need to leave that nice warm bed......just pick up the phone off your nightstand and adjust your thermostat.

Here is a link that might be useful: Ecobee website


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RE: Looking into dehumidifier - what are the considerations?

I never considered the steam from baths and cooking as humidity sources, unless they are looong showers and boiling water. Am I wrong? I would suggest using bath fans and exhaust fans to pull the steam out of the bathroom and from the stovetop while cooking. That would surely alleviate them as humidity sources.

I'm no pro....but I think ionized has it right. Set it up to add it later if you find out you need it. I think the right a/c will suit you fine. I doubt you really need a dehumidifier in the mid atlantic and a tight house should help keep the humidity OUT. I think that is more the cause than from showers etc.


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RE: Looking into dehumidifier - what are the considerations?

@cindywhitall- I would have concurred prior to my research & thousands of years of human experience but now am in the midst of building a tight home & keeping air out is paramount, but the flip side is that air has no way out also.

Therefore, merely opening windows 'airs' things out but then opens the envelope for outside humidity to enter essentially not changing any humidity levels at all.

I was also surprised that human breathing also contributes to CO2 /humidity so we need a good air exchange solution in addition to dehumidification.


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RE: Looking into dehumidifier - what are the considerations?

As the building envelope is tightened up, all of those things become significant, human/pet transpiration, cooking moisture and use of sinks, showers, dishwashers....

Cooking with open gas hobs produces much more moisture than with electric power. Cleaning does not contribute much in comparison to other residential sources except for compulsive cleaners.


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RE: Looking into dehumidifier - what are the considerations?

build tight, ventilate right.
opening the windows adds to the humdity
load and the efficiency exits out the window.

prepare for fresh air, if blower door testing
shows need for fresh air then use ashrae 62.2
to determine strategy.
fyi your house blower door number & sq ft should
be about the same, IF the house is tight.
and if it will need fresh air.

will you have ducts tested when house is tested?
duct loss should be 5-10% not the ususal 30%+

you should visit hvac-talk & post to teddybear.
he steered me to ultraire 70h whole house
dehumidifier that really makes a difference in
the shoulder seasons we are experiencing currently.
little need for a/c so little dehumidification
by 15seer ac & vs air handler. RH rises with just
a/c on to mid 60's with whole house dehumdifier
RH stays 45% while temps stay cool.
my operating costs are about $17 a month.
btw..can't talk costs on hvac-talk but pro answers
from all climates. good information site.

best of luck.


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RE: Looking into dehumidifier - what are the considerations?

@energy_rater_la: thanks for the feedback.

Having lived all these years with humidity & not knowing any better except to turn on the A/C, I'm trying to get an incremental step up in IAQ. However, preliminary research here & on HVAC-Talk makes me believe 'optimum' isn't cheap.

I am concerned that if we wanted optimum air, it's going to run into the thousand$. Not cheap.

So a modest improvement in dehumidifying & evac-ing the cooking smoke with a good vent hood while opening the windows like our forefathers would provide that modicum of improvement I am looking for without breaking the bank.

So my quest is to weight if dehumidification alone can occur with only an advance heat pump vs. a standalone whole house DH vs. the enchilada of whole house DH + ERV??


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RE: Looking into dehumidifier - what are the considerations?

as in so many things..the answer is depends...

I've been advocating stand alone dehumidifiers for a long time. not whole house..but the ones you buy and put in a central location and empty as they remove humidity.

they work well (2000 sq ft per unit) in an open
floorplan with doors open. close them off they
dehumidify the rooms they are open to.

personally, I went with mid efficiency unit
with vs ahu for dehumidificaion..and I was happy with it.
then I got a deal on a whole house dehumidifier..
didn't even use it until last month when a/c wasn't
running & RH shot up sky high in the house.
now..it is comfortable, not sticky.
comfort is more important to me as I get older.
if I were younger & concerned about children in the
house..the focus would be healthy house.
putting a price on these things is hard.

I see folks spend thousands on crown moldings
and crap hvac..and can't afford utility bills.
it just depends on your focus.

in my quest for building tight enough to be efficient
and where is the add fresh air line of tightness..
this is what I've found. here in La. .35 air changes per
hour add fresh air. other states have .25 ach some
programs promote unreal ach. all in the quest to
have us control the air entering the house.
its enough to make you crazy.

I really try to find solutions for people that they
can afford. we have done stand alone dehumidifiers
with great success..depending upon the configuration
of the house. we have also addressed adding fresh air
for pennies on the dollars as compared to erv's.

at this point..you don't know if you need fresh air.
not until you test & determine fresh air changes per hour.

erv's & whole house dehumidifiers with fresh air intakes
are not the only solution.

you should look at some of the studies of different
dehumidification strategies on buildingscience.com
some of them are quite eye opening.

where are you in your building process?

best of luck.


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RE: Looking into dehumidifier - what are the considerations?

@energy_rater_la: thank you for the feedback.

That was the kind of response & flexibility I was looking for.

We are about go into rough-in in the next week or so.
Not sure when the IAQ & tightness tests are scheduled by our builder.

But until then I will continue researching for the right balance of efficiency vs. budget such as you mention:
Stand-alone DH & the fresh air exchange for "pennies on the dollar."

Would interested in your suggestions on those!


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RE: Looking into dehumidifier - what are the considerations?

dedicated *12x12" filter back grill & filter
located under porch, patio or in soffits
with easy access (to change filter)
not north facing or by area where barbecue smoke
will enter.
*duct size to be determined by amount of fresh air
needed..6-8" flex duct
barometric damper *setting determined by
amount of fresh air needed (*blower door test
results converted into achnatural & ashrae 62.2
damper installed in flex line connected to
return air plenum

fresh air. filtered. measured. dehumidified
before entering living space.

say two bath fans going & stove vent.
barometric damper (like skuttle 216)
opens full amount needed* as fans
shut off, damper adjusts to lesser
need for fresh air.

damper can be set to allow set amount
of fresh air entering at all times
or just when house enters negative
pressure.

costs approx
filter back grill & filter 50-75
duct 25-30
damper 150-200
mastic to seal everything up 15

cost by hvac co to install 200-300

stand alone dehumidifier energy star size dependent
upon floor plan. and size of house 200o sq ft per dehumidifier. home depot lowes...200 & higher

can locate inside utility room with
dedicated drain.
or if r/a is chase style and big
enough locate inside r/a and tie into
drain for hvac if possible.

hows that sound?


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RE: Looking into dehumidifier - what are the considerations?

@energy_rater_la - I wanted to take some time & digest the air exchange/dehumidifier solution you suggested.
And also make sure I have summarized it below correctly.
So when I go talk to my builder & the HVAC guys, I can articulate the strategy.

Again, appreciate the feedback to do my own cost efficient process to filter, measure, dehumidify the air before it enters the living space.

Supply List
1) Stand Alone DH dependent on sq. footage ~ $200+ (guessing per 2000 sf)
2) Damper (ex: Skuttle 216) ~$200
3) Ducts (6"-8") ~$20
4) Filter back grill & filter ~$50-$75
5) Duct sealant (Mastic) ~$15

Assumptions & Dependencies associated with:
1) Need to locate hose to drain somewhere (utility room?)
1a) Alternative is to place drain hose in return air chase & tie it into the HVAC drain
2) Barometric style damper can be set to allow adjustable amount of fresh air entering in sync with bathroom or vent hood usage. >>> More when fans are on, less when fans are off.
3) Duct size determined by blower door test to achnatural & ashrae 62.2 guidelines.
3a) Damper installed in flex line connected to return air plenum
4) Dedicated ~12"x12" filter back grill & filter located under porch, patio or in soffits - allows access to change filter - & not north facing or by area where barbecue smoke
will enter.

Questions:
#1 above) Can a portable DH really do the job stuck in a utility room? Wouldn't it need to be out in the open & centrally located & one for the upstairs also?
#3 above) Where is the single duct connected to & where is it going & what is it doing?
#4 above) Looks like the back grill is placed outside of the interior building envelope - what is it used for?


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RE: Looking into dehumidifier - what are the considerations?

Alternative ways of doing it including analysis:

http://www.buildingscience.com/documents/reports/rr-0215-dehumidification-systems-research-results

http://www.buildingscience.com/documents/reports/rr-0214-conditioning-air-in-the-humid-south-creating-comfort-and-controlling-cost


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RE: Looking into dehumidifier - what are the considerations?

On my list of reading ionized! thanks for reminding of that commitment!

Thanks again!


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RE: Looking into dehumidifier - what are the considerations?

Questions:
#1 above) Can a portable DH really do the job stuck in a utility room? Wouldn't it need to be out in the open & centrally located & one for the upstairs also?

the layout of the house determines placement.
as your house is over 2000 sq ft, more than one
dehumidifier (stand alone) would be needed.

#3 above) Where is the single duct connected to & where is it going & what is it doing?

single duct.
one end is connectet to 12x12 filter back grill with filter.
this duct has barometric damper
the other end of the duct is to return of duct system.
it is filtering (filter in fbg)
measuring (barometric damper)
and dehuimidifying (air into return air)
fresh air before it enters the house.

#4 above) Looks like the back grill is placed outside of the interior building envelope - what is it used for?
filter back grill is used
to change the filter of the fresh air
you are adding to your home.


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RE: Looking into dehumidifier - what are the considerations?

I'll add a couple of things since it has been mentioned elsewhere.

You can consider either the barometric activation (which covers every venting source) or electrical. With electrical, you would connect the elec damper to your, say, kitchen exhaust at a speed something like 400cfm (might be Low, might be Medium depending on the vent you purchase).

You might also consider installing an inline fan in the vent after the damper. This will help overcome any 'drop' in pressure due to filter and piping losses.

You might also consider installing an electrical heater (thermostatically controlled) to preheat this outside air before it gets to the furnace. This might also be a part of the inline fan.


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RE: Looking into dehumidifier - what are the considerations?

Posted by ionized (My Page) on Fri, Oct 19, 12 at 16:23
Alternative ways of doing it including analysis:
http://www.buildingscience.com/documents/reports/rr-0215-dehumidification-systems-research-results

http://www.buildingscience.com/documents/reports/rr-0214-conditioning-air-in-the-humid-south-creating-comfort-and-controlling-cost

Finally read these cover to cover.

The push for stand-alone DH in concert with fresh air circulated through a central HVAC actuated damper for cost & performance effectiveness is very strong.

Definitely, gives me some some data points to talk to our HVAC contractor & builder.

great stuff...also certainly supports energy_rater's position.

Thanks again!


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RE: Looking into dehumidifier - what are the considerations?

Those are some nice studies according to what I remember. It has been a while since I went over them carefully. We all know that no matter how good a cooling system can be at removing moisture, there are times and places where it can not dehumidify well enough for the health people or the good of the structure. I was surprised at how poorly their expensive, staged cooling system performed compared to an inexpensive dehumidifier.

Case studies being what they are, the results of other individuals may vary depending on climate, construction and lifestyle. Though I have lived all over the place on the climate map, Energy_rater and I both live in relatively humid environments now.


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RE: Looking into dehumidifier - what are the considerations?

@ionized: My builder seems to have 2 mindset when it comes to HVAC equipment - either pay for the most advanced equipment or do things the old fashion way (open windows to vent).

However, these 2 whitepapers proves strongly that there are middle grounds in dehumidifying a house without great initial & operating expenses.

So while we acquiesced on the 18 SEER Trane Heatpump, we'll take a harder stand on dehumidification control & not accept any more high price equipment added to the mix.

A good damper + humidistat + stand-alone dehumidifier placed in the hallway closet or conditioned attic is the line we will draw in the sand.


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RE: Looking into dehumidifier - what are the considerations?

"@ionized: My builder seems to have 2 mindset when it comes to HVAC equipment - either pay for the most advanced equipment or do things the old fashion way (open windows to vent)."

Some people are binary thinkers and the rest are not ;-)


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RE: Looking into dehumidifier - what are the considerations?

the article that Ionized linked was an eye opener for
me back in 08 when it was released.

(http://www.buildingscience.com/documents/reports/rr-0214-conditioning-air-in-the-humid-south-creating-comfort-and-controlling-cost)

I printed it out & took it to building science classes
in state to question Joe Lstubrick (sp) about it.
it was from Joe, that 2000 sq ft per stand alone dehumidifier sizing was obtained.

conditioned attic?? please explain OP
hallway closet would have to be louvered.

we have gone on about dehumidification..but
what types of insulation are you using..and where?


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RE: Looking into dehumidifier - what are the considerations?

**the article that Ionized linked was an eye opener for
me back in 08 when it was released.
(http://www.buildingscience.com/documents/reports/rr-0214-conditioning-air-in-the-humid-south-creating-comfort-and-controlling-cost)

I printed it out & took it to building science classes
in state to question Joe Lstubrick (sp) about it.
it was from Joe, that 2000 sq ft per stand alone dehumidifier sizing was obtained.**

Eye opener for me also.
The question I still have is that will I need a 2nd stand alone upstairs since most stand-alone DH can only handle about 1400 sq. ft.


**conditioned attic?? please explain OP
hallway closet would have to be louvered.**

Do you think a stand alone DH be put behind a grilled partitioned/cutout/slot in a wall vs. a dedicated louvered closet? Space consideration here :)


**we have gone on about dehumidification..but
what types of insulation are you using..and where?**

Sorry, I was thinking about my sealed conditioned crawl space when I wrote that for some reason. Haven't inquired about specific ratings but they should meet or exceed for Earth Craft certification standards. Insulation are as follows:

1) Attic's roof plane will be sprayed foamed.
2) On top of ceiling in all other areas - Loose filled cellulose
3) Walls - Dense Packed Cellulose
4) Crawl space - 6mm Poly Vapor barrier on floor & sealed to walls.
4a) Foundation wall - R10 XPS insulation or equivalent on this
4b) Sill plate - foam sill sealer
4c) Rim joist - spray foam
5) Air sealing details will be applied in all other fine areas


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RE: Looking into dehumidifier - what are the considerations?

The question I still have is that will I need a 2nd stand alone upstairs since most stand-alone DH can only handle about 1400 sq. ft.

I would think that you would need two stand alone
dehumidifiers.

Do you think a stand alone DH be put behind a grilled partitioned/cutout/slot in a wall vs. a dedicated louvered closet? Space consideration here :)

you need as much communication between dehumidifier
and living space as possible. limiting the amount of
air that reaches dehumidifier limits amount of dehumidification for the space.

this is not making sense to me:
1) Attic's roof plane will be sprayed foamed.
2) On top of ceiling in all other areas - Loose filled cellulose
if insulation is at roofline, then additional
insulation on attic floor isn't necessary.
insulation at roofline if installed properly will
create unvented semi conditioned attic.
do you plan to have both vented and unvented attic
in the house?

trying to get your thread back on track on hvactalk.
don't let alarmist de-rail the thread.
explain to teddy bear the insulation situation.
if you direct your comments to him, you will get
the benefit of his expertiese.

personally I think if you are going to the expense
of foam insulation..then whole house dehumidifier is
a strange place to cut corners. in the long run I think
it would be something you'd regret.
just based on my experience with these types of homes'
performance & comfort. it won't be as easy later to
install dehumidifier to its best install.

best of luck.


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RE: Looking into dehumidifier - what are the considerations?

Posted by energy_rater_la (My Page) on Thu, Oct 25, 12 at 11:51

this is not making sense to me:
2) On top of ceiling in all other areas - Loose filled cellulose >>>
if insulation is at roofline, then additional
insulation on attic floor isn't necessary.
insulation at roofline if installed properly will
create unvented semi conditioned attic.
do you plan to have both vented and unvented attic
in the house?

Intuitively, I always thought this was the prudent way to approach using foam: roof line only & then on top of the attic floors with loose cellulose?

Anyhow, I will clarify with my builder this weekend.


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