HVAC Question...

HollaGeo

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Oct 7, 2005
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316
History:
Late-Winter 2009 the wife and I finished the attic. It's basically a loft with a bathroom and walk in closets. The problem was last Summer (2010) it was a heat factory up there. I had two 12,000 B.T.U. portable A/C's going at full blast all Summer long. It BARELY kept up with the heat. I have looked into those ductless air conditioners. I'm sure it would do the job, just a financial hit we don't need right now. What are some other options we have??? I was thinking a whole-house attic fan to suck the heat out. If the heat wasn't there the portable A/C's would be fine. Help...
 

mike243

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Apr 3, 2009
Messages
123
Re: HVAC Question...

sounds like you got the problem solved,now find out how to remove the heat from your attic,we put a 2 ton split in a 2nd story home with about 800sq'.in 90+ weather it cant keep up.120+ invading on 3 sides & folks dont want to know the truth.a attic fan with a thermostat will make life easier & less $.most house dont have enuf ventilation for summer time.dont beleive me go up on a hot day with a thermo or put a outdoor wireless unit up there & watch it,easy indicator for any season
 

lncoop

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Apr 18, 2010
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5,147
Re: HVAC Question...

How much and what kind of roof venting do you have?
 

tswiczko

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Feb 15, 2009
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838
Re: HVAC Question...

There are several different manufacturers and types. I would use a solar powered cost a little more but you don't have to pay to run it.

Also make sure you are well insulated, and do not have any air infiltration as this could exacerbate the problem.
 

rbh

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Mar 21, 2009
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7,939
Re: HVAC Question...

Anytime you build in the attic area your asking for alot of heat build up in the summer.
What kind of insulation do you have would be the first question I would ask, but I am thinking that the issue may be that when you built this area you did not leave a big enough air gap between the inside and outside walls and ceiling to roof, and as incoop mentioned what do you have for ventalation??
You may want to check your roof end vents to see if they are big enough and that the air holes in the sofiting are moving air.
"BUT" the big one is how many of those wirly gigs do you have on the roof to pull out the heat build up???

Ventilation devices can be active or passive. Turbine vents are passive ventilation devices. Other examples of passive ventilation devices are the traditional metal pot vents and the popular ridge and soffit ventilation systems. Passive ventilation devices do not need electricity to work. Whereas, an active ventilation device could be an electric powered whole house fan or a powered roof ventilator.

Turbine vents consists of a turbine mounted on a sheet metal cylinder. They are normally installed like roof line vents along the face of the roof. When the wind blows, the turbine spins which draws air up out of the attic. Passive turbine vents need wind to be effective, but active turbine vents are not dependent on wind. Turbine vents are round metal vents with fins in them. They normally stick up from the roof surface to about 18 to 20 inches. The fins are actually located in a dome shaped structure that spins when the wind blows across it. The faster the wind, the faster the turbine will rotate. Turbine vents are effective in replacing the hot air in your attic within minutes. Wind blows across the fins in the roof turbine and it exhausts the heat build up.

The mechanics involved in the air movement is very simple. During warm weather, the air present inside the attic heats up and since warm air rises, it tends to rise up. When the turbines rotate, they suck the warm air out through the vent thereby bringing out a drop in temperature in the attic. Turbine vents have been vastly used for many years in residential, agricultural, commercial and industrial buildings. They are cheap and easy to install and can pump out vast amounts of air from the attic.

Let us consider a small 12 inch diameter turbine vent. When a constant wind speed of 5 miles per hour is blowing across its face, it can remove almost 350 cubic fee of air per minute. Even with the lack of any wind, the vents would still allow warm air to drift up and out of the attic. But the volume of air removed would be considerably lower. Though the statistics might not impress you much, it is proved that for a moderately sized home it will do just fine.

It is quite natural for people to think that the vents would leak during a rainstorm. Every rainstorm or even a rain shower is accompanied with wind, which will make the turbines spin, so that should blow off the raindrops off the vent. The same applies for snow too.

Roof turbine vents are cheap. The average cost of a high quality roof turbine would be about $50. Also the time taken to install one is just about 15 minutes. Good quality roof turbines will be hassle free for years as they will have permanently sealed ball bearings. If you want the turbine vent to be secured better to your roof, you can always opt for the one with metal braces. The metal braces extend out beyond the turbine and do a good job of stabilizing the turbine even at high wind speeds.

Learn more about Vent and Roof Turbine Vents at the Vents site http://vents.advice
 

lncoop

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Re: HVAC Question...

Yep, and you need a mix of active and passive because the active venting draws the heat toward the roof and the passive venting allows it to escape. There's a lot of good info on the old superhighway about the best ratio of one to the other under various circumstances.
 

Lion hunter

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Re: HVAC Question...

I had the same situation as you. Finished attic that was almost impossible to run ducting without a major overhaul and window a/c units woudn't hardly cool. Most of the passive airflow was blocked off when the PO finished the room. Attic room was about 400 sq ft (12' wide X 32' long). I installed turbine vents in the roof (one on each side of the house) and it cut the temp by 20 degrees. Now a 10000 BTU window unit will cool the room pretty well. Took an hour tops to install both vents, and I think they were about $30 each at the orange store. At some point I will install a ductless unit but it's not in the budget now.
 

lncoop

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Re: HVAC Question...

There ya go. You know heat rises, so give it a way to rise right on out of your upper room.
 

SparkieBoat

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Re: HVAC Question...

if the 2 12000 btu units barely kept up last year..assuming you have a well ventilated attic..why not just add a 18000 btu unit to one of the 12000 btu units and that will be your cheapest way to provide ac up there...there is not cheaper way to provide ac.
 

NYBo

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Re: HVAC Question...

Those portable units aren't particularly efficient since they do not recirculate the already-cooled room air. Hot outside air is constantly sucked into the room.
 

Lion hunter

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Re: HVAC Question...

Those portable units aren't particularly efficient since they do not recirculate the already-cooled room air. Hot outside air is constantly sucked into the room.

I'm with you on this one. I had a portable unit and unless you live in a very very dry climate the water tub has to be emptied every 3-4 hours. They are also loud and very expensive. Even with the exhaust vented outside they still build up a lot of heat that just kills the fan motor. I got a window unit after that died and for 1/4 the price it works just as good and will do the job until a mini-split fits in the budget.
 

SparkieBoat

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Re: HVAC Question...

they are not as efficient..but the difference is only slight..you are wrong about them not recirculating the already cooled air..I have never even seen one that sucks a significant amount of air from the outside. I have seen some that have a small hole that can be opened or closed to allow a small amount of outside air into the system. but the filter is on the INSIDE on the face of the unit because this is where the air is drawn into the system. hot outside air will not be sucked into the room if the unit is sealed good when installed. I would recommend a 2" thick piece of styrofoam around the edges of the unit and use foil tape to seal
 

NYBo

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Re: HVAC Question...

The one I have (not being used since I have central a/c) uses a 4" vent hose that blows a tremendous amount of air outside. The make-up air has to come from somewhere, and that somewhere is outside, hot air.

Are you talking about a window unit, perhaps, Sparkie? I'm referring to ones like this:
41Mh1mm4n-L._SL500_AA300_.jpg


Of course, maybe the OP is referring to window units also.:redface:
 

SparkieBoat

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Re: HVAC Question...

I assumed we were talking about window units...the unit you have pictured is not very functional and probably no where near 12000 BTUs...but you are right about it drawing in make up air...
window units are the most economical way to get AC into a room.
 

NYBo

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Re: HVAC Question...

There are portable units even larger than 12000 BTU. Rather pricey to feed, I imagine.
 
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