55 degree difference up/downstairs

joeyknuckles · 12-01-2006, 11:23 PM

My house, like many others, is cold on the main floor and burning up on the second floor. I assumed that it was the old 'heat rising' story that caused it and hadn't really looked closer until tonight. Now I think that there is an actual problem...read on for the description

Currently my first floor is about 66 degrees and my second floor is about 76 degrees (this is actually about 5 hours after my wife closing all the registers on the 2nd floor!). The vents/registers on the second floor really blow the air out hard, to the point that they whistle if you close the registers. The vents on the first floor don't blow very hard at all, its almost as if the heat is just radiating out of them. The air that comes out of the 2nd floor measures 156 degrees while the downstairs only measures 99.5 degrees.
So basically the upstairs is blowing much hotter and harder than the main floor.

Here's what I can tell you about my heating system. Its a forced air gas furnace located on the main level of the house. The duct work for the first floor is in some sort of flexible insulated pipe that was poured into the slab when the house was built a couple years ago. The duct work that goes to the 2nd floor goes inside the wall up to the attic.

Would there be a damper somewhere that is deflecting all the air to the upstairs? There is very little duct work visible in the house, really just a couple feet at the intake end of the furnace and a piece on the output side that heads from floor to ceiling. I would imagine that if there is a damper, it would be in here..but it is wrapped with insulation that I don't want to tear apart unless I have some reassurance that I'm going to be able to find some adjustments here.

#CARRIERMAN · 12-03-2006, 02:04 PM

Hi joeyknuckles

I don't want to make you think you have an easy fix. The biggest problem with slab duct work is that when it deteriorates it leaves a cavity in the screenings or sand, whatever they used under your pad. When this happens all the air is dissapated under the pad. If you have a favorite HVAC company, you will need to have them come give you some options as far as a new duct system for your downstairs. They may be able to install a surface duct system to you satisfaction. Sorry if this is not what you wanted to hear, but I didn't want to mislead you.

Good luck
Rusty

joeyknuckles · 12-03-2006, 04:12 PM

Ouch. I do have a question on that though. This house is only 3 or 4 years old, would the duct work have detiorated already? Also, I think that the current problem has existed since the house was built. This is what was leading me towards the idea of some sort of restriction in air flow. The fact that all of the upstairs vents are good and all of the downstairs ones have equally restricted flow leads me to believe that the restriction is between the furnace and the point where all of the underground ductwork branches. Since the 1' foot or so of ductwork that is not underground is closed and the rest is underground, I don't know what I'm dealing with. Is there a chance that there is some sort of damper? Would I be able to install some sort of booster fan into the downstairs feed?

I'll have a closer look soon. I'm going to take a look and see if I can see anything from inside the furnace or through the hole I cut for the thermostat that I installed recently for the thermomister humidifier.

mdshunk · 12-03-2006, 04:18 PM

Worse comes to worse, you can always have a plumber with a sewer camera come scope out the situation for you. In a 3-4 year old house, that sounds more like a catestrophic design problem, or a damper that you've overlooked. Did the original installer put a sticker on the furnace? Maybe you can call him and ask what's the scoop? If not, maybe the original GC will remember who the HVAC guy was.

redline · 12-03-2006, 06:09 PM

Are you able to remove the grill off of the first floor registers and take a small mirror/flash light and "look" down the passage for either blockage or damper?

joeyknuckles · 12-03-2006, 08:58 PM

It seems that the downstairs isn't as restricted as I thought. For giggles I took a look at the filter. I just replaced this filter 2 weeks ago, but it was completely caked with a chalky layer. I replaced the filter and the airflow to the downstairs was improved. The chalky covering, I believe, is caused by my recently installed in-duct humidifier. We have hard water, so I'm assuming that this is a calcium deposit or something. I will look at installing an inline water filter prior to the humidifier. The humidifier is the mister style that sprays a mist that is evaporated in the duct. The instructions explicitly said not to feed it with softened water...something about the softwater's ph level would break down the valve or nozzle or something like that.

As far as the remaining disparity between the upstairs and downstairs temperature, I believe that it is partially due to things I can't change (the fact that heat rises). I do think that I can improve it though. I got to looking around and realized that there is no return vent on the first floor. The closest air return is at the top of the stairs. I think I'm going to add a return near the baseboard on the first floor. I can pull this off pretty easily since the furnace closet in the garage shares a wall with the living room. I figure that I could shut this new return off in the summer and have it open in the winter to pull the cooler air from near the floor. I'm also thinking about adding another supply register in the living room through the same wall. Currently the living room only has one register and it is located at the other end of the room. I believe the room is about 20' wide and aroun 15' long (but is completely open to a breakfast nook and kitchen, so the room is really about 40x20' with 3 vents spaced relatively evenly along the 40' wall).

coolmen · 12-03-2006, 09:51 PM

go to the attic where the main duct is close back the damper you say is there. you need to balance the system.

PATMAN · 12-20-2006, 11:31 AM

It sounds like a very bad duct design to me. If there is not a damper to the upstairs you could have one installed to choke off the supply to the upstairs rooms, this should redirect the air to the downstairs rooms. You can add a blower to the downstairs ducts but I would only do that as a last resort. choke down that upstairs air. You have the right idea adding a return, be careful since it's in the garage area that you seal the ducts really well so you don't get car exhaust into the return.

Christopher · 12-20-2006, 12:40 PM

joeyknuckles,

Quote:

The air that comes out of the 2nd floor measures 156 degrees while the downstairs only measures 99.5 degrees.

You have clearly identified the problem. In fact I am inclined to believe that you have at least two problems. First, the furnace is running too hot due to insufficient air flow. I look for oil furnaces to deliver air at 140 degrees and gas furnaces to deliver air at 120 degrees or less. If the gas furnace is a high efficiency condensing type, the operating temperature is fairly critical and they are designed to run cool compared to furnaces of yesteryear.

Second, it sounds like the insulation on your ground floor ductwork is crushed.

I would not close any second floor vents as your furnace is already running too hot due to insufficient air flow.

Quote:

I think I'm going to add a return near the baseboard on the first floor. I can pull this off pretty easily since the furnace closet in the garage shares a wall with the living room. I figure that I could shut this new return off in the summer and have it open in the winter to pull the cooler air from near the floor. I'm also thinking about adding another supply register in the living room through the same wall.

These are both good ideas.

If your system has an A/C cooling coil, you probably need to have the blower wired for high-speed year round to over come the air flow resistance this poses in your system.

...Christopher