Author Topic: Heat and a/c for shop  (Read 10269 times)

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Offline TealaG

  • Posts: 66
Re: Heat and a/c for shop
« Reply #30 on: July 17, 2017, 06:40 PM »
Any thoughts on the benefit of a motorized attic fan to vent the heat out of the attic?    I have a one story house, I'm looking to get the ceiling (attic) above the attached garage insulated.   I'm then thinking of pumping the hot air out of the attic using a solar powered fan.   Would that help cool the garage at all?   The fan claims to help reduce the amt of A/C you need in the house, help preserve the insulation from breaking down and reduce the wear on the asphalt shingles by reducing the heat beneath them.   

I had an insulation installer give me some strange story about my cellulose insulation and how it was flying through the air of my house through the air conditioning system.   Not once have I seen cellulose flying through the air of my house and I've actually had the A/C inspected 3 times in the past 2 years for unrelated issues and no one has mentioned cellulose in the system.   I also look at my white fluff in the attic and it looks fine, not breaking down, not being sucked into the A/C.  It looks as cloud like as it did when it was installed.    Now I'm scared that other sales folks will try to give me other strange stories and I won't realize it.   

Offline RKA

  • Posts: 916
Re: Heat and a/c for shop
« Reply #31 on: July 17, 2017, 08:01 PM »
Yes, it will help.  That attic can get north of 140F on a 95F day.  As long as you have adequate soffit openings to allow make up air into the bottom of the attic, the fan will help.  Solar powered fans typically can't move much air, so I might consider just running an electric line up there for the fan and stick with a traditional thermostat modulated fan.
-Raj

Offline antss

  • Posts: 1369
Re: Heat and a/c for shop
« Reply #32 on: July 18, 2017, 01:48 AM »
What part of the country are you in?  That's going to make a difference in the advice.

Offline jtmorrow

  • Posts: 36
Re: Heat and a/c for shop
« Reply #33 on: July 18, 2017, 09:06 AM »
I installed a whole house attic fan in my house, to save on A/C costs at certain times of year.  It does work, and works well, as long as you have sufficient venting in the attic.

In the middle of the afternoon, it won't help you much, as you need to open a window or door for it to draw air, which will be very warm air.

The ideal times for an attic fan to run are morning and evening.  I could never get much breeze coming through my house with all the windows open, so the attic fan forces the air up and draws in cooler air (after it cools outside).
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Offline HarveyWildes

  • Posts: 579
Re: Heat and a/c for shop
« Reply #34 on: July 18, 2017, 09:36 AM »
I installed a whole house attic fan in my house, to save on A/C costs at certain times of year.  It does work, and works well, as long as you have sufficient venting in the attic.

In the middle of the afternoon, it won't help you much, as you need to open a window or door for it to draw air, which will be very warm air.

The ideal times for an attic fan to run are morning and evening.  I could never get much breeze coming through my house with all the windows open, so the attic fan forces the air up and draws in cooler air (after it cools outside).

We run an attic fan for summer cooling.  Since they started tracking nighttime low temperatures in Colorado, there have only been three nighttime lows of 70 F or above, so we nearly always dip down into the 60's.  That makes an attic fan very effective at cooling the house down at night, both cooling the house and the attic.  By 5 the next day we might creep up above 80 in the house on a hot day, and on an exceptional 100+ degree day we might get up to 85 F by 7pm or so.  Recently we got a couple of room minisplits for those days, but we really don't use them much.

Offline RKA

  • Posts: 916
Re: Heat and a/c for shop
« Reply #35 on: July 18, 2017, 11:23 AM »
Just to clarify, jtmorrow and harveywildes are discussing whole house fans installed between the living space below the attic and the attic.  These are different, not solar powered and they move a lot of air.  You open windows throughout the house to draw in cool evening or nighttime air, run the fan for 20 minutes and you've effectively evacuated the hot air in the house with cool air from outside.  You can keep running it if you like the breeze, otherwise flip the switch and shut it off when the house is cool.  As mentioned, this works well if you live in an area that has pleasant night time conditions (and you don't suffer from allergies).  Assuming you have a cold season, you're going to want to seal off the fan from the attic side to limit air (heat) from escaping during the winter months. 

But I would begin with improving the attic circulation by installing a fan on the roof.  This would run throughout the day during peak sun.  That will limit the heat build up in the attic and the spaces below the attic.   
-Raj

Offline RussellS

  • Posts: 183
Re: Heat and a/c for shop
« Reply #36 on: July 18, 2017, 03:36 PM »
As mentioned by another, I think the concept of ATTIC fans and whole house fans got mixed up.  They are different.  An attic fan only ventilates the attic.  It has a hole in the roof, or maybe just the ridge vent, and draws air in from the soffit vents.  No connection to the main house space.  It replaces the stale, hot air that builds up in the attic with less hot air from outside.  It would help cool the attic a little because the hot air in the attic is a bit hotter than the moving air outside in the wild.  Not sure about this concept of protecting the insulation.  Fiberglass or cellulose is inert.  It is unaffected by about everything as long as it does not get wet.  And the roof should keep the rain out.  That is a different story.  Fiberglass or cellulose does not care about temperatures.  100, 150, 200 degrees, makes no difference to it.  Its inert.  Does a 2x4 care if its 75 or 100 or 125 degrees?  The ridge vents and soffit vents are a passive way to reduce the heat and ventilate, remove moisture, in the attic.  A electrical powered fan would improve on this.  But not sure it improves much to matter.

Whole house fans are different.  They ventilate the living space in the house.  NOT the attic.  As stated, they draw cool air in through windows, doors and shoot it out through the roof.  Assume you would make a hole in your living room ceiling and in the roof to exhaust the air.  And have ducting that goes directly from the living space through the roof and outside into the open air.  Never touching the attic air itself.  It works the same way as the ridge vents and soffit vents on your roof except applied to the living space.  And most likely always powered by an electrical fan, blower.  And as stated, this works best when it gets cool and nice at night, you turn on the fan, it gets all the hot air out of the house and allows you to sleep nicely.  You turn it off in the morning and throughout the day the house and outside air all heat up so not much point in blowing hot air through the house all day long.  Wait until night time again and then pull in the cool night air and blow out the hot inside air.  Great passive, active cooling system if your environment allows it.  If you live in the Midwest where it gets 98 degrees and 90% humidity in the day and 88 degrees and 89% humidity at night, it does not work well.  Its hot sticky muggy humid.

Offline TealaG

  • Posts: 66
Re: Heat and a/c for shop
« Reply #37 on: July 18, 2017, 07:34 PM »
I live in Houston Tx...100 degrees outside and it's painful to be in the garage.   I was really looking at roof top vents that forces the hot air out of the attic and hopefully cools the garage (or prevents it from heating up as badly).

I also looked at some high powered fan to pump the heat out of the garage to the attic.   But I'm trying to start small.   I'm searching for an insulation installer to put the insulation above the garage.   I also would like these attic fans, if I can fit them between my solar panels.   I think anything more than that would be a larger investment.   

Offline jtmorrow

  • Posts: 36
Re: Heat and a/c for shop
« Reply #38 on: July 18, 2017, 08:16 PM »
Sorry, I didn't mean to sidetrack.  I thought one of the posters meant a whole house attic fan and I was clarifying how it wouldn't be what the OP wants.

A powered attic fan (vs a solar one) would help a little, but I'm not sure very much, without having plenty of insulation first.  I've seen powered attic fans that can be controlled by a thermostat, so at least it could turn on automatically at, say, 100F... but it will only get you so far if the temperature that afternoon is 90 or 95F.
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Offline JerryW

  • Posts: 36
Re: Heat and a/c for shop
« Reply #39 on: July 19, 2017, 10:04 AM »
Tealag,

I live in Katy, Texas (a suburb of Houston for those who may not know).  My shop area is about 400 sq ft and shares a roof, but no walls with the house.  The roof has radiant barrier decking and ridge vents together with soffit vents that allows a good exchange of air in the attic without use of a fan.  It is quite effective in reducing the attic temperature during our hot summers here.  The house and shop are fully insulated (walls and ceilings) with fiberglass insulation. The combination of more moderate attic temperature with good insulation helps a lot in the living area that is also cooled with central air.

However, the shop space is not air conditioned and I quickly found that in spite of the fact that it had the advantage of the cooler attic and full insulation, the heat still was a major problem.  On hot summer days the heat was such that I was dripping sweat on my work and cast iron surfaces.  Not a good situation!  I added a window air conditioner to a window that is not visible to neighbors or the street.  The air conditioner works very well - makes it very comfortable.  I run it only on the days that I am in the shop. There is one major heat source that I have not taken care of yet, and that is an un-insulated garage door with a western exposure.  I probably should have given that priority over adding the window air conditioner.

I did consider and would have preferred a split unit, but went with the window unit because of its lower cost.  As far as your cellulose insulation goes, I would not be concerned with that at all.  I suspect that because cellulose is less common in our climate, people may just have never dealt with it.  I suggest that you look at ways to circulate the heated air from your attic.  Ridge vents with soffit vents are very effective and maintenance free.  If you can add radiant barrier to the roof decking so much better.  I think you said your shop ceiling and walls are insulated.  If not, adding that would help a lot.  Any air conditioning system should then make your shop bearable and pleasant in our hot summers.
« Last Edit: July 19, 2017, 10:09 AM by JerryW »
Jerry

Offline TealaG

  • Posts: 66
Re: Heat and a/c for shop
« Reply #40 on: July 19, 2017, 08:11 PM »
Jerry...thanks for your thoughts.   I actually have a cheesy, insulated, west facing garage door.   I won't say that the insulation doesn't help, but ...I wish it helped more!    I need to find someone to blow more insulation in the ceiling of the garage and I definitely think it's a strong first step.    The issue is finding a qualified person to do it.   

The house was built in 2012,  so it has radiant barrier etc.   I added the attic hatch insulation cover where it unzips to allow you to enter the attic and tries to block the heat from coming out of the hatch.   The hatch also appears to have insulation board. 

Part of my issue with a minisplit is having a location to put the outside unit where the HOA won't complain (I'm allowed 1 minisplit system OR a window unit, but it has to be covered up and in that location, it could become difficult to create a covering since it's in an unfenced area between my house and the house next door - I can't fence it off so I might have to add more bushes on the property line to cover it up)

Then...there's the $$$.   I don't do this full time...I'm just a part time hobby person.  My main crafting is weaving, knitting, sewing etc.   I just build tables or custom tools for my crafting!   I would eventually like to convert my garage into a "makerspace", which would have a CNC, 3D printer and such.   But at the rate I'm going, I may only be able to tolerate that garage 50% of the year.  :(

One step at a time...I'll keep working on getting the insulation in first, since I can't do anything without that.