Uneven heat in house.


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Old 01-24-07, 03:08 PM
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Uneven heat in house.

Hello,

I have an problem with uneven heat in our house. Our house was built in 1988, we have the original forced air furnance, 80% efficiency I believe. We bought the house two years ago and the home inspector stated that since the people we bought the house from did not use the house during the winter, the insides of the furnance have rusted a bit and it is a bit more worn that usual for its age. Our house is 1530 sqft.

We set the temp in our house at 68. The thermostate is on the first floor in the main room. The temp on the second floor is usually (during winter here in Michigan) around 60 - 62 degrees. Too cold!!!

We have four air vents on the floor in the main room, two in the kitchen, one in the bathroom and one in the laundry room. There are four cold air returns on the first floor. On the second floor, there are two hot vents and one return in the master bedroom (where the 60-62 temp was taken) one vent and return in the bathroom in the master bedroom, one air vent and one cold return in each of the other two bedrooms, and one vent in the spare half bath.

So, is there anything I can do to fix this problem and have a more even heat? All the duct is metal, and the duct in the basement is exposed. I've tried to close various heat vents and I tried to cover various cold returns to force the warm air to circulate better, but thus far I've not figured this out.

As a side, I've been thinking that it is time to replace the furnance due to high gas/electric costs and the fact that it seems to always be running. It seems to work okay, but I'm thinking a more efficent furnance may be cheaper in the long run and the contractor may be able to fix this uneven heat problem at the same time?

Thanks for your thoughts.

Jeremy
 
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Old 01-24-07, 07:13 PM
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Two stories with basement need two units! If you are going to replace main system here is your change to do it wright! Have 3 contractors do heat load on home to size BOTH units and duct in the attick!
 
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Old 01-25-07, 07:39 AM
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Originally Posted by airman.1994 View Post
Two stories with basement need two units! If you are going to replace main system here is your change to do it wright! Have 3 contractors do heat load on home to size BOTH units and duct in the attick!


What? I've never heard of anyone have two units, especially in a 1530 sq ft home. My parent's have a 2500 sq ft home with forced air, one unit, and it is pretty evenly heated.
 
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Old 01-25-07, 12:08 PM
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These days it is common to install multiple furnace units in a home that has multiple living levels. The "reason" is that it is easier to do it that way than to properly design AND install the ductwork for a single furnace system.

Depending upon several factors it may be that having two furnaces may be the least expensive (capital costs) option at this time. What you need is a complete heat loss calculation and duct sizing calculation made on the house. It may be that the existing ductwork is simply too small for the required heat distribution. The configuration of your home may preclude the installation of the "proper sized" ductwork for a single furnace.

Undersized ductwork requires higher air velocities to move the requisite volume of heated air. Higher velocities mean more noise and require more power from the blower in the furnace. If your ductwork is not properly insulated it will lose much of the heat in the air supplied by the furnace before it is released into the various rooms and this ends up requiring the furnace output temperature to be higher. Since the amount of heat (in BTU's) that your furnace can provide is pretty much fixed the only way to raise the output temperature is to slow down the blower speed, which of course means a lower volume of air being delivered by the ductwork.

I know this is not what you wanted to hear. It is unfortunate but most homes built within the last thirty years have inadequately sized and insulated ductwork and the builders simply install oversized furnaces with the blowers running at higher speeds in order to compensate. A good duct system will cost as much, if not more, than the furnace itself.

One last thing, bathrooms should never have a return air duct.
 
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Old 01-25-07, 01:30 PM
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One last thing, bathrooms should never have a return air duct.
Thats for sure. I dont think it will pass code anywhere.
im with them . All we put in on a two story home is two units. It works much better than any zone control does The fuel used is much lower and the people like the temp in the home much better.
Have you checked the blower to see what speed it is on ?You could give high speed a try if not on it.
 
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Old 01-25-07, 01:43 PM
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1500 sq. ft needs 2 systems? id like to see the load calc.

MY OPINION
id have a qualified contractor come out and look at the duct design and see about some renovations there, youll probably want to look into a new furnace, Variable speed would be best so that you can fine tune the airflow to the changes in your duct system, and possibly look into a zoning system to split off the two levels if needed. mechanical dampers may be all that is needed and would be a much cheaper option in a smaller home
 
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Old 01-25-07, 01:43 PM
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Now that you mention it, I'm not 100% sure on the bathroom return


Well, we have a few problems. A) it does not appear that any of our duct is insulated. I've been contemplating doing so, but I can only get to the ducts in the basement. B) $$. It costs a lot to replace a furnance. While we are certainly not in poverty, a new funance will cause a serious belt tighting. But, if it will reduce our monthly bills, as friends have indicated, I'd consider it. Rough guesstimate, what do you think this would cost? The second floor is approximately 700 sq ft with three bedrooms and two full baths.

Do you think getting a second unit in the attic and retaining the current furance for the first floor while insulating the duct work would, overall, be an economical solution? I.E. not terribly costly upfront and yet save us on our electric and gas bills?

It would seem that if the main, older furance was only running the first floor and if we were able to insulate most of the duct in that system, the cost would drop a fair amount. And, the second unit would be a much more efficient unit, thus over monthly costs should drop, right?

Plus, as another bonus, our termostat is ten feet from our fire place, which we like to use but if we do use it the upstairs gets very cold. A second unit would seem to solve this.


BTW, thanks for the responses. This board always comes through for me.
 
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Old 01-25-07, 01:47 PM
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Originally Posted by nomore9to5 View Post
1500 sq. ft needs 2 systems? id like to see the load calc.

MY OPINION
id have a qualified contractor come out and look at the duct design and see about some renovations there, youll probably want to look into a new furnace, Variable speed would be best so that you can fine tune the airflow to the changes in your duct system, and possibly look into a zoning system to split off the two levels if needed. mechanical dampers may be all that is needed and would be a much cheaper option in a smaller home


Thanks for the opinion. I guess I'll have to get some estimates. I assume they will give me a load calc as part of the estimate?
 
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Old 01-25-07, 01:51 PM
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yes, your gonna need to get a thorough walk around, not just a furnace estimate. make sure they take a heat loss and gain. and make sure that they can properly size the ducting and give options on what to do there since that sounds like your biggest problem.
 
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Old 01-25-07, 02:05 PM
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Might go to http://warmair.net there you can compare fuel cost for where you live . As to what fuel to use for a new unit. On any of the duct in the home like in the basement. dont put insulation on them let the heat out in the home . Even the registers in the duct in the basement help heat the floor in teh home . So its not a loss
 
 

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