CONDENSATION PROBLEMS 1

[huylersm]

I HAVE CONDENSATION PROBLEMS IN MY HOUSE, AND AM SEEKING ADVICE ON HOW TO FIX IT. MY HOUSE IS NEWER (WE HAD IT BUILT IN 1995), AND THE HOME IS VERY TIGHT. ANOTHER ISSUE IS WITH THE GAS-FIRED FORCED AIR FURNACE. IT DOESN'T HAVE AN OUTSIDE AIR INLET. IT ONLY SUCKS AIR FROM THE BASEMENT.

IS THE AIR INLET (OR ABSENCE OF) TO THE FURNACE THE PROBLEM? (IE: NOT ENOUGH OUTSIDE AIR TO BALANCE RH?)

IS THERE ANYTHING I CAN DO TO FIX IT, IN LEIUE OF BUYING A NEW FURNACE?

THANKS FOR THE HELP!

 

[walkes]

Do you mean that you have no combustion air intake to the furnace? Are you also missing a ventilation duct to the return side of the furnace? Is all of the return air from the house going through your basement?

If your house is very tight and exhaust fans are running (bathroom or dryer vent) you may downdraft products of combustion back into the space. you should have a Carbon Monoxide sensor near your furnace room (and near sleeping areas).

What you should require is both a combustion air intake and a ventilation air intake. Combustion air should terminate near to the burner of the furnace. Ventilation duct should terminate in a return air plenum such that the outside air mixes with return air before it hits the burner. After that is done you can run the exhaust fans in your house to draw air in through the furnace (leave furnace on fan continuously). Your space RH will drop. (Another thought would be to have an exhaust fan controlled by a space humidistat)

Just some ideas.

 

[CESSNA1]

BUYLERSM: What do you mean by a "condensation problem"? Is there moisture on windows or elsewhere? Where is the house located? how long have you had the "problem"?

Regards

Dave

 

[gregha04756]

The absence of a dedicated combustion air inlet may be a code violation. With respect to the condensation problem, a heat-recovery ventilation unit such as a VenMar should do the trick. I had a ventilation unit in my house, they do an excellent job controlling humidity and making the living space more comfortable.

Good Luck,
Greg Hansen

 

[Clymber]

I also have a gas-fired furnace installed in my basement garage. Return air is pulled into a closed plenum at the bottom of the unit, with no opening for fresh/outside air. The unit also has no dedicated outside air supply for combustion air; infiltration leakage through the garage door provides the outside air. A well-sealed door could reduce the available OA and cause both performance and safety issues, as stated above.

 

[huylersm]

To answer all of your questions --
Right now, in the winter, I have alot of problems with condensation on the windows (it runs down the windows) - ever since we moved into the house. If I run the ceiling fan in the house, it helps a little. The RH is ~ 50%, and the Temp is normally around 70-72 deg F inside. The furnace shuts down during the day while at work, to ~ 60deg F, per our programmable thermostat.

I live in north-central PA, just a half-mile from the NY border. My furnace has a cold air return from the house (upstairs) going back into the furnace. The furnace has a vent going to the outside through the roof, but there is no fresh-air intake for combustion. The furnace has louvers on the front cover. I have a CO detector at the top of the basement stairs, leading into the house.

I have been told that I could tap in a piece of duct that is going to the outside of the house into the return duct. But the problem is that I would have to run the pipe about 20 feet. And I am not sure how big it needs to be.

Thanks for the help!

 

[CESSNA1]

BUYLERSM: Your problem is probably typical for your area. I had this problem in Southeast Pa and Southern New Jersy. If you have single pane windows the problem will be worse than with double of triple pane windows. The boundary layer on the inside of the glass is approximately equal to the outside temperature. This causes moisture in the inside of the house to condense on the windows. The inside of the house has a higher humidity ~50% due to cooking/people/humidifier/heater(combustion gives off water vapor)/etc. This moisture condenses on the window pane (I have also seen ice form).

There is also convective flow as the warm inside air is cooled by the window pane boundary layer and sinks to the floor giving a fresh supply of humid air to the window pane.

The solution is not always simple try:

1. lower humidifier setting
2. install vinyl double or triple glazed windows.
3. install storm windows
4. install "plastic storm windows" over the outside and/or inside of the regular windows.

An outside combustion air supply, although desirable and required by code someplaces, will not help the problem. You need to lower the inside humidity and/or reduce/eliminate conditions that cause the water or condense on the window.

Go to the psychometric chart and look up the dew point for the air inside you house. It is at or lower than the ouside temperature.

Good Luck
Regards
Dave

 

[Rodale]

Is the furnace "natural" draft or "induced" draft, is there a power venter? Is the furnace 80% or 90+%, does it use PVC pipe to vent the products of combustion and have a condensate drain? Is there a gas water heater, natural draft or power vent?

ALL fuel burning appliances need adequate combustion air. If the home is so tight that there is not enough air for combustion, you will have a serious carbon monoxide potential.

The references above to adding an outside air intake to the return air system helps with combustion air, but really is make-up air for the bath exhaust fans, kitchen exhaust fan, clothes dryer..... If you use these appliances while trying to heat your home and water, you will most likely be sucking air down the flue pipes. Then the bathroom, laundry and kitchen become the home's chimney. NOT GOOD.

The products of complete combustion are carbon dioxide and WATER vapor. Your windows may be an indication of the problem.

Have a QUALIFIED professional look at the system. Your and your families lives are worth the investment.

 

[huylersm]

Thanks, CESSNA1. I just this afternoon thought about looking up on a psychro chart. (my HVAC background is very limited, that's why I posted the thread). You are right - the Tdp is about 50-55degF, based on the inside temps of 70-72degF and RH ranges around 50%.

I would say that it is about right.

I am still concerned about the furnace though, and wonder if I should try to add a fresh air intake, instead of sucking air from the basement...

THANKS TO ALL - - HAPPY HOLIDAYS!

 

[CESSNA1]

BUYLERSM:

Unless a heater is located in a vented attic or garage where it already gets outside air for combustion, I would suggest an outside air supply for combustion air. Since yours is in the basement you can run a duct from the outside.

Regards
Dave