Two furnaces?


Old 05-08-02, 05:00 PM
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Two furnaces?

Heres the deal. My basement is too cold. I have a two story house with a full basement. I have a 90+ furnace set up to control three zones of heat: zone 1 is upper floor, 2 is main, 3 is lower. In the winter when we are heating all three floors, everything is fine. Problem is during late spring and summer when we are ising the AC for the main and upper floor, the basement is too cold, even though the zone for the basement never calls for air conditioning.

No matter how hot it gets outside, the basement never climbs above 65. I am sure this is due to the cooler airconditioned are stratifying down into the basement. (We do keep the door leading to the basement closed all the time). Normally in hot weather this may seem like a good thing, but it is just too cold for my wife and kids to be interested in being down there. It would be nice to keep it around 72-75 degrees and I dont want to keep windows open for humidity reasons. What I really need to do is be able to heat the basement while I AC the rest of the house. This seems really stupid to me, but I cant think of any other way.

My question is this. Is it possible for me to install a second small furnace and use it to heat (heat only, no AC) the basement zone? I would disconnect the basement zone from the main furnace making that furnace just two zone, but I would have to share the cold air return. I am wondering if I can share the cold air returns with both furnaces or would I have to have separate return air ducts run just for the new basement furnace? I also have no flue since my main furnace is direct vent, so I would need a recommendation on a small direct vent furnace (vent out a side wall) that is not too large for a 1500sf basement.
By the way, I do not want to install a gas fireplace in the basement, so please don't recommend that.

Thanks in advance.
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Old 05-08-02, 07:31 PM
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Hello: Doctorhifi

A direct vent {thru the wall vent} heater may just be the correct answer to correct the condition you described and obtain the results wanted.

If the basement has some above outside ground wall clearance, a direct vent heater should be available to fit the need. These units are relatively easy to install. Check with your local heating company on these types of heaters used in your area.

You should have it professionally installed. Doing so will insure the unit and the installation meets all local codes.

Should you or someone else reading my reply, asks me about unvented or ventless heaters or may be wondering about using or installing a ventless heater. I personally do not recommend using or installing any type of ventless or unvented heater for any reason nor under any circumstances period.

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Old 05-08-02, 10:50 PM
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It is apparent you're still cooling the basement even though you have the zone closed. The things I suggest you look at are, duct leakage, uninsulated ductwork and an open return.

The volume of air in the house remains constant, the same is true for each room and level. You cannot blow either heating or cooling into the house without taking out the same volume of air. Hence the need for a return and supply vents. Take a piece of paper and put it up to the return vent in the basement. If the paper is drawn to the vent, it tells you the same volume of being brought in must be replaced from the cooling system. Even if you closed the door to the basement and the zone. Solution, close the return vent. I'm assuming you have returns on the other 2 zones. Not only will you make the basement more livable, but you'll probably drop your cooling bill by 15 to 20%.

The next thing to check are your vents in the basement. Put your hand up to the supply vents in the basement. It wouldn't be the first time a servo didn't close completely. If you feel air coming out, close the vents. Then run you hand around where ducts are joined. If you feel cool air coming out, tape the joint.

The last thing to check are the ducts that are exposed in the basement. Put your hand on them. If they feel cold or wet, then you're transferring the air conditioning through them to the basement. Solution, insulate the exposed ductwork.
Old 05-09-02, 04:35 AM
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Thanks for the tips. You should know:
1. All duct work in the basement ceiling is insulated; however the basement duct work is transite under the slab. I saw it being installed it was surrounded by 1" foam, nothing more. Dont know of any way to insulate it more than it already is.

2. There are 3 return air vents in the basement: Are you saying the cool air from upstairs is making its way into the basement via the return air vents? If I close the return vents how do I keep the air in the basement from becoming stale? My house is Class 1; very tight.

3. Have checked dampers for basement zone. It closes all the way, but it isnt a perfect seal there is still some leakage.

4. I have my furnace set to circulate the air in the house every few hours. This helps keep things comfortable in the winter, but is probably adding to the coolness in the basement. I will set it not to circulate.

Old 05-09-02, 06:15 AM
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The volume of the air in the basement remains constant. That means, if a certain volume of air enters the 3 returns in the basement, the same volume of air must enter the basement. The vacuum effect created by a return is so powerful that it's capable of drawing air passed a closed window. However, it will always seek the source of least resistance. In your case that will be the cool air that is being distributed within the cooling system or upstairs.

There are some simple tests you can do to determine if this is true. If the piece of paper is held up against the return while the unit is on, then go to the door that separates the first floor to the basement and use a smoke stick or cigarette and move the smoke around the perimeter of the door. You will notice the smoke being blown towards the basement. That will indicate that the cool air upstairs is being drawn to the basement because of the negative pressure created by the returns and positve pressure created by taking air from the basement and sending it upstairs. Because where is the air going if the returns are drawing air and the supply vents are closed in the basement? Then try taking saran wrap and covering the 3 returns and doing the smoke test while the unit is on. You will notice a significant difference on how the smoke behaves. The door air leakage will represent only a small portion of the air needed from the upstairs to equalize the pressure difference created by the returns in the basement.

I am aware of building regulations in your State concerning tight houses that either require fresh air supply or air to air exchangers. The issue concerning Indoor Air Quality (IAQ) is quite serious concerning tight houses. I do not pretend to be an IAQ expert, however, those same experts would be quick to point out the negative pressure created by the returns in the basement pose a far greater health issue than adequate air exchange. Check the Dept. of Energy or EPA websites on IAQ. There are several studies that will concern you by Oak Ridge National Laboratory, Tennessee Valley Assoc., ASHREA and nearly every major University in and out of the U.S. The topics you wish to read up on is moisture and/or mold problems.
Old 05-10-02, 03:05 PM
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Basements are always colder than upstairs whether you have a ducted forced air system or not due to the mass of the walls and concrete floor that are always kept cool from the ground. I doubt that the air conditioned air from the upper floors are migrating into the basement becuase even if they are and you find the source and close it off, the basement will still be cold.

A very easy solution would be to install a few electric baseboard heaters or electric wall heaters that would easily raise the basement room temperature to your 72 degrees. Adding a second furnace would also work but requires holes in the outside wall, gas piping and a vent.

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