considerations for replacement furnace


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Old 10-28-10, 10:53 AM
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considerations for replacement furnace

I am looking to replace my existing GAS furnace for my 2 story home this year.

I have talked to a few companies and here's the story I'm getting.

My Trane guy is telling me to get the XV95 because the variable speed motor will help my 2 story home. Actually the problem I have is that the bedrooms on one side of the 2nd floor are colder in winter than the other side. I don't see how, but he says the variable speed helps that.

ALSO, I may have to replace the A/C unit in the future and he says it is IMPERATIVE to get a variable speed blower because the A/C will require it. Is that accurate, and applies to all brands??

Because I priced out another brand and they wanted to give me the non-variable speed blower motor and they knew I might do my A/C in the future, too. He offered the variable speed as an option, but the cost was considerably more.

Also, do I need a new t-stat with the XV95 because it is a 2 stage? Would that be a DIY option? Because we did just put in a programmable t-stat a few years ago.

I'm also a little worried about the condensing aspect of the furnaces, because this is in the attic. One neighbor said he had one that wasn't installed real well (I guess) and the water was not flowing out properly and he was getting shut offs.
What should I check on to make sure the condensing unit is installed right?

The million dollar question, of course, is which brand should I get?
 
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Old 10-28-10, 11:26 AM
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Your concerns are reasonable.


Frankly the first contractor wasn't being honest with you and was trying to manipulate you by providing biased information, in my opinion.

Pretty much all forced air furnaces offer different fan motor windings which usually create four possible fan speeds. When the AC is on, the high speed windings are energized and when the heating mode is on, a lower speed winding is selected.

A variable speed motor allows the fan speed to be controlled with the same motor winding.

So the contractor was handing you a line when he said a variable speed motor was needed for AC use.

A variable input furnace MIGHT even out the temperatures around the house. By having a low input available, the burner and fan may remain on a much higher percentage of the time and allow more heat to be circulated into remote rooms.

It might overheat other rooms too, perhaps.

It would be better to have a good repairman evaluate the problem for you and see if it can be solved directly. For example, it's common for much of the heated air to come out of the vents nearest the furnace, leaving little for more remote parts of the duct system. restricting the air flow near the furnace might pressurize the duct system and allow more heat to flow to remote rooms. Also, restricting the air flow into the room with the thermostat would cause the furnace to stay on longer, giving remote parts of the house more time to warm up.

This is called "balancing" the system.

It might be that a higher fan speed could be selected on your existing furnace which would help circulate air into those more remote rooms as well.

But such adjustments can cause problems. Restricting the airflow can cause the furnace to overheat, and increasing the fan speed can cause the furnace to operate too cool which can cause problems.

So I wouldn't recommend a DIY effort to make these adjustments.
 
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Old 10-28-10, 12:55 PM
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Can be a number of things why the far room may not be warm. Have you had an energy audit done to see if you have any insulation in the wall/ceiling. Lack of return or number/size of supply for that room too.

Also, Is that room above a garage?

Where are you out of?

Variable speed blower may help, but we need to see why that room is cold. Two stage furnace may help, since the furnace run longer on first stage, and hope they do a Manual-J on YOUR home to see what size of equipment it needs..

I've seen homes with older furnace, and they were way oversized, so it don't run much and didn't get a chance to warm up rooms. (Long run time is ideal)

What is the make/model of your current t-stat? Chances are it may already be a two stage stat.

Plus thing of variable speed is quiet/slow speed when the fan is in "ON" mode. I run my fan 24/7 in the heating season, and all the rooms in the house are with in -/+1˚ from one another. With the fan running the whole time, the air in the home is mixed and balanced out.

YOu don't have to have variable speed for A/C... However, it does give a much better SEER rating, and comfort if you use the humidity control for A/C.
 
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Old 10-29-10, 09:44 AM
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Thanks for the ideas so far, I appreciate it Buying a furnace is a big deal for me.

Temp Differences: I've got 2 cooler bedrooms (and hotter during summer). They are on the cold side of the house (less direct sunlight), and yes one is over the garage and yes, there may be a little insulation (missing or not enough) at the edge of the roof over these rooms. My first thought was to adjust the furnace to get more air over there. I actually just found out I have dampers on the ducts in the attic. So I shouldn't mess with those? What I probably should do is figure out how to add insulation.

The other issue is that there is a noticeable difference in temp btw the 1st and 2nd floors. Now I am beginning to understand how the variable speed helps by running longer and distributing the air.

BTW, how long should a furnace run, generally?

Manual- J...wow, I thought that was an urban legend. The HVAC people I've talked to don't want to do it.

TStat
: I looked at what I have (Hunter 44260) which I'm guessing is not compatible w/ the 2 stage furnace. I'd love recommendations on what to get & where.

Any other tips on what to check when they retrofit for the condensing unit? I'm a little confused because they said the new PVC flue pipe does not have a vent cap on it. So rain & debris are not an issue??

What's the story on contractors? Some only sell one brand, others have a preferred brand...but would sell me something else if asked.
 
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Old 10-29-10, 01:03 PM
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Originally Posted by blue3
yes one is over the garage
Look to see if you got any between the room and garage. In our house we had ZIP of insulation, I rip the whole garage ceiling down and added insulation in there and inuslated the ductwork as well.

I actually just found out I have dampers on the ducts in the attic. So I shouldn't mess with those?
Is there insulation wrapped on the ducts itself? If the dampers are closed, open them up to get more air flow. Do you have returns up there?

BTW, how long should a furnace run, generally?
On a mild day, maybe 20 minutes, and on the coldest day pretty steady to non stop.

Manual- J...wow, I thought that was an urban legend. The HVAC people I've talked to don't want to do it.
If they won't do it, the shop else where till you find one that does it. If you hit a brick wall, then you can download the $50 home owner one and do it yourself and see how close they are.




TStat
: I looked at what I have (Hunter 44260) which I'm guessing is not compatible w/ the 2 stage furnace. I'd love recommendations on what to get & where.
Get away from Hunter.. They make great fans, but not t-stat.

I'd get the Honywell RTH7500 or RTH7600 sold at Home Depot or online, or upgrade to a real t-stat from Honeywell. VisioinPro TH8320. Otherwise, if wire is an issue to fish then go to the Honeywell IAQ.

Any other tips on what to check when they retrofit for the condensing unit?
Getting a new A/C?

I'm a little confused because they said the new PVC flue pipe does not have a vent cap on it. So rain & debris are not an issue??
Correct, I take it they are planning on going up to the roof? When they do the two pipe, then the intake needs to point down to keep the rain out.
 
 

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