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Old 07-25-2012, 08:48 PM   #1
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Need Input on Whole House Fan


Hi, All.

I have a 2600 square foot ranch-style home in Northern CT. We have central air, but the unit is undersized by a bit (the home was originally about 2100 square feet and then two small additions were put on) and runs pretty much constantly once the daytime temps are up above 80.

The biggest problem we have is that we have to continue to run the AC overnight even though the temps have dropped down considerably because the temps inside the house are still in the high 70's or above. I'd like to install a Whole House Fan to give us an opportunity to quickly cool the house at the end of the day and leave the AC off. The electric bill is completely out of control over the summer because of the AC and the pool pump. If I can cut the AC usage way down, that will heavily offset the electric usage.

According to the reading I've been doing, I should have a fan that's capable of moving about 7500CFM of air, and should have at least 8 square feet of ventilation space available in the attic. The attic vent space should be an issue because I already have a powered fan in the roof that gives almost a couple square feet by itself. Add to that all of the soffit venting around the entire house, and the 8 square feet requirement is fulfilled easily.

I found a fan on Amazon.com that could move the right amount of air, but the review of it said it was flimsy, loud, and not something you would want to use "frequently". What I'm hoping to find here is recommendations for a fan that will provide the specs I need along with being *reasonably* quiet and still not overly expensive.

Also - if anyone has recommendations on how I could wire the Whole House Fan and the roof vent fan together so that they will come on at the same time, that would make the airflow go even more smoothly to cool the house. And, by together, I don't mean "always together". The roof vent fan is currently wired with a thermostat to evacuate hot air from the attic based on attic temp. I would still want that. At the same time, however, I would also want to be able to energize the fan when the Whole House Fan was on too.

Thanks in advance!!!

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Old 07-25-2012, 08:49 PM   #2
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I failed to mention that the roof vent fan is in the same area of the attic where the Whole House Fan would be located. So, the wiring is in close proximity.

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Old 07-25-2012, 09:24 PM   #3
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Need Input on Whole House Fan


I think it is going to be hard to find advise on a whole house fan. They were used alot before air conditioning was the norm. At least in my area that is the case.
I just have one thought, if you open the home up at night and try to use the whole house fan you will be letting all the humidity in you have worked so hard during the day to remove. The removal of humidity takes more engergy than the dropping of the temp.
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Old 07-25-2012, 09:47 PM   #4
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Need Input on Whole House Fan


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Originally Posted by turnermech View Post
I think it is going to be hard to find advise on a whole house fan. They were used alot before air conditioning was the norm. At least in my area that is the case.
I just have one thought, if you open the home up at night and try to use the whole house fan you will be letting all the humidity in you have worked so hard during the day to remove. The removal of humidity takes more engergy than the dropping of the temp.
I re read my post and i did not want to sound so negative with the "hard time finding advise". I guess I was meaning it would take some one who had been in the field for some time. Those old timers so to speak I don't see surfing the fourm. But you never know. either way I just bumped you to the top. Good luck
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Old 07-25-2012, 10:00 PM   #5
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I re read my post and i did not want to sound so negative with the "hard time finding advise". I guess I was meaning it would take some one who had been in the field for some time. Those old timers so to speak I don't see surfing the fourm. But you never know. either way I just bumped you to the top. Good luck
I'm familiar with the weather in "your neck of the woods" a I've done a fair amount of work there in the summer months. It's common for the temp and humidity still be high even at 10pm. Fortunately, here, the humidity is not as oppressive most days (or should I say nights). So, with regard to letting in the humidity, I don't see that as being a major issue. As far as finding useful input and advice, I'm confident there are lots of folks that could help since these are not "a thing of the past". They're still actively used quite a bit, especially on homes where retro fitting central air would be ridiculously expensive.

I'm keeping my fingers crossed.
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Old 07-25-2012, 10:44 PM   #6
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Need Input on Whole House Fan


Do you have a boiler or gas water heater? I only ask as I rember when I first was getting into the trade there were a few still being used around here. I would from time to time run into boilers and water heaters which soot themself up by the whole house fan pulling a negative pressure and preventing the burner from burning correctly. I could also see Carbon monoxide being pulled in from the draft hood or barometric damper. I did never experience that though
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Old 07-26-2012, 08:19 AM   #7
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Do you have a boiler or gas water heater? I only ask as I rember when I first was getting into the trade there were a few still being used around here. I would from time to time run into boilers and water heaters which soot themself up by the whole house fan pulling a negative pressure and preventing the burner from burning correctly. I could also see Carbon monoxide being pulled in from the draft hood or barometric damper. I did never experience that though
Oil-fired hot air furnace and oil-fired water tank. I am considering changing out the hot water tank to electric but I have to do the math on operating cost, investment cost, and the time to ROI.

The only time a negative pressure "should" be encountered is if the windows / doors of the house aren't open when the fan is on, correct?
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Old 07-26-2012, 08:37 AM   #8
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Need Input on Whole House Fan


you might want to consider an economizer for your hvac system instead of a wholehouse fan. Additionally, a barametric damper to the attic would not be a bad idea also. This would positivily presurize your home and CO would not be a problem... just a thought.

as to the undersized ac system, check for proper sized ducts (supply and return) by doing a manual J calculation (software on the net) and a manual D calc. I would suspect that the additions were not properly ducted and that your return(s) were not re-sized for the additional square footage or maybe even the tonage of your ac system. Do the checks and I think you will find the answers as to why the ac system runs all the time. Of course please understand that ac systems should run 100 percent of the time, when the outside temp is a the design temp. Manual J will help you figure out the design temp!!!!
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Old 07-26-2012, 09:11 AM   #9
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you might want to consider an economizer for your hvac system instead of a wholehouse fan. Additionally, a barametric damper to the attic would not be a bad idea also. This would positivily presurize your home and CO would not be a problem... just a thought.

as to the undersized ac system, check for proper sized ducts (supply and return) by doing a manual J calculation (software on the net) and a manual D calc. I would suspect that the additions were not properly ducted and that your return(s) were not re-sized for the additional square footage or maybe even the tonage of your ac system. Do the checks and I think you will find the answers as to why the ac system runs all the time. Of course please understand that ac systems should run 100 percent of the time, when the outside temp is a the design temp. Manual J will help you figure out the design temp!!!!
I've "sort of" already been down this road.

There was a "mud room" added on (addition 1) that added about 150 sq feet. No ducting was added for this area as it basically was just an enlargement of an existing space. It faces West, has a decent amount of tree cover, and minimal windows. It has a poured slab floor which actually helps with keeping the space cool. Extra heat load here is not "high".

The second addition was much larger - about 350 sq feet. 2/3 of this space is in the form of my "office" and the rest is where the master bathroom was extended. It's on the South end of the house, significant tree coverage, and minimal windows. For this area, there was a new foundation poured (crawl space, about half as deep from grade as the rest of the basement). No ducting appears to have been added for the bathroom, although it was relocated. There was a duct added for my office space, but no return installed. This room does get warmer than the others, but I don't find it problematic if I leave the door to the master bedroom open so that the air will circulate via the return in there.

Third change to the house is that two bedrooms were "re-partitioned" into three. A duct was added to the new bedroom, but no return. This room gets warm in summer and cold in winter because the door stays closed at night for sleeping.

The unit is a 2.5 ton, I believe, and I've done all of the heat load calculations (as has a professional) and arrived at somewhere around 3.5 ton being the required size to cool this house.

In the summer, when the temp is at 90, the house will continue to warm throughout the day and will only slightly drop in temp overnight. It's undersized, period. The furnace is older, I haven't decided on whether I'm staying with oil or not, and I have to spend the cash wisely. So, a new AC unit is not in the budget at this time.
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Old 07-26-2012, 09:15 AM   #10
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Forgot to mention that an economizer would essentially do the same thing as a Whole House Fan except that it's more "automatic" since it can automatically open ducts to draw outside air and use it for cooling instead of having to use the compressor to manually cool warm air and recirculate it.

It's also about twice the cost (or more) for the unit itself and that doesn't necessarily include any / all of the ducting required.

EDIT: The cost of the CONTROLLER is more than double the cost of a fan. Still have to factor in the ducting, the dampers, and the motors... At that point, why wouldn't I just install a new, larger, much more efficient unit?

Last edited by meburdick; 07-26-2012 at 09:35 AM.
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Old 07-26-2012, 11:41 AM   #11
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Need Input on Whole House Fan


very cool (pun intended) that you have had the load calcs done!!!.

and that you already looked at an economizer.

sounds like you are set for a whole house fan!!!!! and maybe an ac upgrade in the future.
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Old 07-26-2012, 02:25 PM   #12
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very cool (pun intended) that you have had the load calcs done!!!.

and that you already looked at an economizer.

sounds like you are set for a whole house fan!!!!! and maybe an ac upgrade in the future.
I did the calcs myself using an online resource that we very detailed. The "professional" that I had come and take measurements didn't measure the windows and their compass directions, just concerned themselves with square footage. When they came back and said that their calculations indicated 2.5 - 3 ton, I challenged it with the work I had done and they sort of went "oh yeah... that would make sense".

Haven't actively looked into the economizer... Just did some quick reading about what they are, what they're capable of doing, and then did a quick price lookup on the controllers.

So, yeah... I think the WHF is the best bang for my buck right now, and that's what prompted me to post. Once I find one reasonably priced and reasonably quiet in the size range I need, I can order it and get to work putting it in.

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