Variable Fan Speed for Central A/C?

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My furnace is a Carrier 58MXA Weathermaker 9200 (http://www.carrier.com/CAR_ENT_PRODUCT/product.htm?MODELXMXA ), which has a variable speed blower fan. I just had a York Olympian A/C unit (I know it's builder quality, but the price was right and it came with a 10-year parts AND labor warranty) installed, and it's working fine except the second floor is hotter than the first.
Because the furnace is in the basement and the air for the second floor has to travel all the way up to the attic and come down from the ceiling (it was how the duct work was done by the previous owners), the air force is much weaker than the first floor. None of this is a surprise.
What is a surprise is that even though I have a variable-speed fan in my furnace (which of course also drives the A/C), according to the installers, the fan will only kick in at a single speed.
This doesn't seem right to me. In my other house, the furnace fan ran at two speeds: low for heat and high for A/C. When I questioned them, they made it sound like the newer systems don't do this. Are they right? Any help would be much appreciated.
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VS is VS you can set the speed you need . Did Daves Heating work on it ?
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This is Turtle.
Yea, i think so for she was told she has a Veriable Speed Blower.
TURTLE
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Yoyomama wrote:

floor... the reason: the attic is just above the second floor and the attic has a temp. of about 135-170 degrees in it.. then the heat infiltrates down through the ceiling of the second floor...thr first floor does not have this attic over it and has an airconditioned room over it... so its always gonna be cooler than the second floor........ yes, you have insulation, but you also have too much heat in the attic...
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OP snipped .

WRONG.
That should read: In a home that the HVAC system was not designed correctly, the second floor will normally be warmer than the 1st floor due to the installers lack of intellegence when designing the system.

Wrong again.
First, lets look at basic, simple thermodynamics, before we get into the air flow issues.
Make it simple for you, hot air rises. Cooler air falls.
Now, thats a simple lesson.
Now, lets get into the reason hes got a warmer 2nd floor.
His system is designed wrong. A builder, or a homeower prior to him that had either no clue about what they were doing, or wanted to get out as cheap as possible thinking one unit would do the job, used that..one unit. The upper floor NEEDS a second unit, and any 1st year apprentice can tell you that. The reason is as stated in the basic thermodynamics course shown above. Air, is fluid. It also has a weight, and the duct has resistance. Improperly designed duct systems will create this issue he as, as I have seen many smaller homes with single systems and multiple returns, and while they work so so, a home with more than one floor, needs the additional help a 2nd system will give.
In a case like this, a single system might work, provided he has oversized returns to insure that the air from the 2nd floor will make it to the furnace in a manner that allows for a high volume of turnover on the 2nd floor...this will work fine in the summer...but what about the winter months? Again...a SECOND UNIT is needed.
Ten to one, hes got a serious case of stagnation, and no amount of monkeying with the existing unit will fix that.
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In the responses to this thread there is no direct mention of Manual J and Manual D. Is there any reason to doubt the system specification that would be produced by J and D - and if the resulting design shows that the system will be OK with a single unit is there any reason to doubt the design?
Geoffrey

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You seem not to understand me.
My question was simply a challange to your suggestion that two units MUST be used in a two story house.
Geoffrey

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You don't *have to* use 2 systems in a 2 story house, you can use 1 with zoning, but one by itself without zoning is not gonna give you the balanced temperatures between all rooms both upstairs and downstairs. Simple physics....heat rises....With a single system, you might have everything balanced to maintain a constant temp within 1 or 2 degrees during the summer, but all bets are off in winter and vice-versa. With 2 systems that are correctly sized and installed, that goes away
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Many thanks for your reply - I have been using Manual J etc to design for cooling only (the temp here never goes below 6C in winter). I just wanted reassurance that having a single unit was not completely stupid. I have been told by some installers that cold air can not be sent up ducts against gravity but I suspected that this was wrong. My system will have individual room thermostats with proportional control as well as balancing dampers (and a static bypass damper).
Geoffrey

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Don't let gravity get you down. Have you heard of the space elevator? Within 10 years, we will be building space elevators - strong cables that stretch into outer space about 60,000 miles.
http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html
Lud .
On Tue, 06 Jul 2004 18:25:07 GMT, "geoffrey cohen"

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geoffrey cohen wrote:

In my country, it's a necessity. I don't know about in yours. Of course, most people here prefer ranch houses on large lots.
It was 110 here today with a 34 dewpoint. No sweaty suction lines here.
Vicki

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P.S.
What is a challange? Something French?
geoffrey cohen wrote:

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Vicki Szaszvari posted for all of us....

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I missedhis reply....oh well...
Again...two are a must here,unless by some chance you have a small place and can get by with a 5 tonner with zoning...

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Not on a properly sized & installed system.
~kjpro~
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Whew...thats a good one, since it is neither builder quality, thats another line based upon the Olympian case, and they dont come with but a 90 day warranty for labor, unless you paid the extra $325 for the extended labor warranty. 10 year parts...again...its 5 parts, and 10 compressor....and big hint..you wont need the parts warranty....:) You didnt say what tonnage...but that would be interesting to know, along with a price....

And you EXPECT it to work?

Umm...bud..you do NOT have a VS motor...you have a multi-SPEED motor..meaning...its got two that is uses...lower for heating, and higher for cooling...thats the way that unit is...

Depends on how its wired, but you do NOT have a VARIABLE speed motor...you have a fixed tap for each speed...and normally, on those..no more than 3...one isnt used. An ICP rep can offer more, if he wants, but you dont have a furnace problem....you have an install issue, and no amount of monkeying with the fan speed will fix that.
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First of all -- thanks for all your input. Yeah, I know the system should have a 2nd unit on the 2nd floor. It'll be another $2500-$3000, which we just can't afford right now. So for the time being, we'll have to make do with a unit that can't work a 100%, so I'm just trying to do what I can to get as much out of this imperfect system.

2.5 tons, 14 SEER, 10-year parts, 10-year compressor, 10-year labor warranties. Didn't pay the extended labor warranty, but most likely, it was included in the price. After the rebates kick in ($200 from York, $500 from energy company), the total comes to $3300. I had estimates for a Carrier Puron unit for $5000 (3 tons, 13 SEER) and a Trane unit (2.5 tons, 13 SEER) for $4500. From all that I've read, Carrier and Trane seem to be the preferred choices, but the 10-year labor warranty seemed like a decent alternative (both Carrier and Trane carried 1 year labor warranties). And I've also read that installation matters more than the brand...

I didn't realize that my unit isn't VS but MS. But that's OK -- what the installers were telling me is that the unit is running at the same speed for both heating and AC. And that's what I have a problem with.

All I want is for the unit to run at 2 speeds, low for heat and high for AC. What do you mean by a "fixed tap for each speed" and "no more than 3"? Are you saying that there are 3 speeds on this unit and that one of the speeds is not used? And what is an "ICP rep"? Sorry for all these questions, but I'm a newbie when it comes to all this.
And as far as branch duct dampers are concerned, yes, I do have these in the basement. They look like semicircles and I can set them at 1, 3/4, 1/2, and 1/4. Right now, both of them are set at 1. Seems like HVAC fella ( snipped-for-privacy@webtv.net) thinks this is a possibility while CBHVAC ( snipped-for-privacy@carolinabreezeREMOVETHIS.com) thinks this is not a viable option. Can you guys elaborate?
Right now, I have half of the vents on the 1st floor closed off, and that's actually making the upstairs cooler. I know I'll never achieve the same temperature on both floors with my single AC unit, but if I can get that temp difference to something like 3-5 degrees, I'll be satisfied. Maybe what I should do is open up all those closed vents on the 1st floor and just use the dampers instead? Seems like that's a more efficient workaround.
As far as an attic fan is concerned, yes, I do have one of those -- it turns on automatically, depending on temperature. It's still hot as hell up there, though. It doesn't help that I have a black slate roof...
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Your unit has several speeds which can be set maybe 2 maybe 4 my lennox has maybe 5 that can be picked from the tap on the furnace, tap meaning a plug in point.
ICP rep , a Carrier sales rep
You might be able to Zone the second floor
Do you have a 2nd fl return.
Are you sure your ducts are sealed and insulated as well as the attic.
Running an attic fan that is to large or with to small air intake venting will pull airconditioned air out of your house, A blowerdoor test will determine your houses air exchanges and weak points, the tech goes around with a smoke stick pinpointing arteas for yu to fix. Air infiltration, negative induced attic pressure, blower door tests are all something Daves Hack Heating never learned and could be giving you problems. If you cut off 1st floor registers you risk freezing your A coil ,
Duct booster fans may be a temporary idea,
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thinks this is not a

Yes, Steve unlike Davey "the moron", knows how a HVAC system is supposed to work.

And by closing off to many registers you could create another problem down the road. (this is like putting cardboard in front of your vehicles radiator)

Try setting it at a lower temperature.
~kjpro~
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