HVAC Folks

I have a 2 story house with seperate HVAC units, obviosly the one downstaris hardly runs but its like a friggin sauna upstairs. It takes about 3 hours to cool down from 84^ when we get home to around 79^..

We have no trees, and basic ventilation in the attic. The upstairs system is in the attic( about 115 - 120 degrees) I imagine. I lost 5 pounds the last time I changed the air conditioner filter..

Last summer I put in an "under eaves" (SP?) fan which blows some hot air out of the attic. It helped a little, but I was curious if you can put two of those in the attic? Like one on each side of the house?

I recall reaading something about that could be a bad thing unless you have a large attic (Mine is pretty manly) but didnt know if it depended on the square footage or something 'scientific' like that..

Its a fairly new untit (5 years)....

Any other info you can give me before I suck it up and call someone?

Your second story is a true story? or is like a cape cod where the 2nd story is the attic?

That makes a difference, and you can have multiple fans, I've got 2 vents in my attic, 2 fans above the house, and a fan above the garage's attic.

I also run the house off of one unit.

no its 2 full "story's" with an attic on top of the second story.

my daughters room is above the garage and the attic above her room, and its always hot as hell in there. I put some more insulation above her room this winter, but it hasnt seemed to help.

The ventilation fan I put in is on the other side so I was going to put one over the eave in the attic above her room so hopefully help..

I'm into commercial HVAC, but mostly the controls side of it, so I don't know a whole lot about what you're asking.

But, do you have enough vents in your eaves to allow the relatively cooler air to be sucked into your attic either by the fans or just natural convecton?

In my old house, the inspector said we didn't have enough. I never got around to adding any. It never caused any problems though.

Ed

Also, if you have the fan way on the other side of the attic from your daughter's room, it could be moving air through the attic on the other side only, thereby not cooling the attic by her side.

Ed

thats what I was hoping, I need to stop by Home Depot cause I recall something on the box the other fan came in about "Dont install multiple fans without X amount of Square Feet"

I know most of you HVAC folks do stuff more complicated than this, I just figured I would axe..

You can also add a thermostat so that the fan doesn't come on until the attic reaches a certain temp. That way its not runnig all the time.

I have heard, but done no research on this that money-wise, you can spend a lot running the fan 24-7. I guess it all depends on the HP.

Ed

There are a couple of other factors in this. One, how is the insulation in your attic and where is it located? Two, I noticed you said it takes three hours to cool down from 84 to 79. I would assume from that statement you are "setting" the thermostat back while you are at work. If this is so you are losing control of the upstairs and all of the heat from your entire house is rising into this second floor and that is what your second floor HVAC unit is having to handle. It might cost you some more money but you might consider letting the upstairs unit run all the time and only setting back the downstairs unit. I have also seen a lot of people run their fans continously and cycle the condensing unit when needed to control temperature. This could help control the stratification of air you are experiencing. It would have definitely helped if you had a single unit because the air could then be re-circulated back downstairs. Your first floor might get warmer but the second would not get as hot.

I would seriously consider leaving the second floor unit on during the day. Letting the temperature rise in a house to 84 degrees has all sorts of long term problems with woodwork, humidity, and mold growth. I would probably recommend never letting a house get above 80 degrees.

If you continue to have problems you could also consider applying the insulation in the attic to the underside of the roof instead of the top of the second floor ceiling. This will reduce the amount of heat transferred into the attic and thus into the house. Also, if you have an attic access ladder make sure it is insulated. This is typically a great source of heat gain.

I only do large commercial but occassionally we are asked to take a look at a residential issue and I also have a house with about the same configuration. I have a single unit installed with zone dampers at each floor. Each floor has a thermostat that controls the zone damper similar to a VVT system. It works great and I don't set back the units at all. The second floor typically is the only unit calling for cooling.

we normally do bump the upstairs up to around 82 when we leave. On the weekends when we are home and leave it on 80/79 it runs nonstop during the day, I will give it a shot though and see if theres a difference

most of my insulation is "good" (I think) I bought a new fan to put above the daughters room, but havent put it up yet, was going to do it early one saturday before it gets 140^ in the attic.

I really think my unit is underpowered. Upstaris we have 4 bedrooms, and 2 bathrooms, The "kids" bathroom is sort of like a hotel bathroom where the "tub & shitter" are in a seperate room and then there is a sink area, they only put a vent in the "shitter room" and the other room is hot as hell.

The closets are fairly big and there is no vent in the kids closets either, and since kids play in the closet, they leave the doors open, and it contributes to the overall "warmth" of the upstairs.

I need to suck it up and probably have a reputable HVAC firm check it out and see about getting a new unit for the upstaris, my power bills are approaching $400/month

Why not get the solar powered attic exhaust fans? They will run off of solar power when the attic temps go above the set point.

Also, put in a radiant heat barrier in the attic. It is a metalic paint that you spray underneath the roof in the attic. It keeps the radiant heat of the sun from penetrating to the attic in the summer. It also helps in the winter by reflecting the radiant heat from your house back into the house. You should be able to find this stuff at your local home improvement store.

Great idea slugger, on the RHB. I didn't know they had a spray-on version. When I replaced my roof at my last house, the roofer offered the decking material with the "foil" type RHB, but I didn't go for it. I have since heard from a fellow I know who replaced a small part of his rof with this stuff that it is noticibly cooler in that area.

I might have to look into the spray kind.

Ed

what type of insulation do you have in the attic? And how thick is it? I have about 12" blown in and it helps a lot.

As for residential units, they still run ideally like commercial units. They run the best when they get 70-80 degree air, the efficency gets very low when the air temp gets higher. As you have seen with your energy bill.

I'm not sure what type of unit you have upstairs but maybe adding a fan and duct over to the unit so it is getting outside air and not stagnet air that is super hot from sitting in your attic.

Then again, you could always transplant some 50 year old oak trees to your yard to shade your house.

In my job with a City, I walk a LOT of houses that are under construction. You can really tell the difference between the houses that have the radiant heat barrier and those that don't. It makes a HUGE difference here in our climates. I Paid the extra to have it installed in mine when our house was built and my electric bill is considerably lower than our neighbors.

the do make a spray on kind. I would suggest hiring someone to do it though. If you are anything like me, I know I would step through my ceiling at least a couple of times while jacking around in the attic tryint to spray it on. Plus, there is hardly any ventilation up there, I imagine the fumes might get pretty bad.

Is the spary-on in something like a normal spray paint can type thing?

I am looking into a MAJOR home renovation/additon project and might look into having it done then- either by them or by me.

Ed

Ed,

I'm not exactly sure, but I think it comes in 1 - 5 gal cans and you spray it with an airless sprayer. I don't think it comes in cans like rustoleum if that is waht you are refering to.

Here is a site to check out. The home page has the home depot logo, so I assume they sell / install it.

http://www.efficientattic.com/faq_rbs.asp

12-15" of blown cellulose insulation and 2 or 3 "whirlybirds" with eave vents will do wonders.

What tonnage is the unit and how many sq ft are upstairs?

Where are you (State)? Are we talking split systems or window A.C. units (Where is the condenser?)? What color are your shingles? What color is your house? Are you near a lake? Etc.

Initial thought is something along these lines: your ac unit is bringing in O.A. and mixing with return air. Maybe something like this:

100deg F - O.A.

80deg - R.A.

makes maybe 90deg F Entering air.

Cool that 20 deg and you will get 70deg F.

Mix that with the 80deg F room air and you get a complaining wife.

Adding vents will help quite a bit. Adding powered vents (fan and louvers) will help even more. That will help increase the air movement thru the space and HELP disapate some of the heat from the structure. However, i agree with the statment to keep that unit running more often. Do you have an off peek meter on your electric (Check into it if you dont, call your elect company. Its like a deduct meter for water irrigation.)?

You could also manifold the two units to have the one downstair pick up some of the load and have the upper one focus on a smaller area.

Sorry i couldnt help more, but i need a bit more info to make any solid judgments.

Residential units don't bring in OA do they?

What's a offpeak meter? Sounds interesting.

Ed

More and more residential systems are incorporating outside air, but it's still very rare on normal houses. Houses are becoming so tight that they need some fresh air input to keep the air quality at a decent level.

Which reminds me, I had to argue with a coworker (I'm 23 and have worked in residential HVAC since I was 8 or 9 with my dad) that our system here at my office didn't bring in O.A., and I have looked at the entire system, it's easily visible. He was also trying to tell me that every residential system brought in O.A. I just shook my head and went on, it didn't do any good telling him different. He's one of those guys that is kind of a know it all, but mostly one that once he thinks something is one way, you can't convince him otherwise. :suicide:

They can. Depends on the type of system.

> Off peek meter for your elect.

I'm not sure as to how they work exactly, but I think of it as like a deduct water meter. (I got a buddy who's an electrician...he checked to see if I had one. I tried to understand it with him be he wasnt even sure how it worked.).