Is 60% Humidity in the Home Too High?
HIGH HUMIDITY 60 % +. Within the last month, I moved into a new house. It has dry walls and not plaster walls. The furnace and hot water tank were installed a week or so before we moved in to the house. Last week we determined that there is a humidity issue when the windows were sweating. We are trying to determine the source of the humidity. The contractor feels it may be the high efficiency furnace. I have a Lennox g61mp. The combustion air is pulled from within the un finished basement. Should the air be pulled from the outside? The gases are vented via PVC pipe which slopes back to the furnace.
Could the furnace be causing the humidity problem? If yes, what could be causing the humidity problem? The installer said it is not the furnace.
Answer…….
Maintaining the proper humidity levels in the home is important not only for health (as indicated on High Performance HVAC Humidifiers Page) but also for the wood products in the home including doors and windows. The quick answer to your question about the furnace causing the humidity problems is no. Gas furnaces and other heating appliances tend to dehumidify the air and do not create any more humidification. I wonder where your supply vents are located and are they directed to blow hot air towards the windows? Condensation is created when the temperature of air is colder than the dew point. A prime place for this to occur is windows and doors. This is part of the reason why many supply vents for forced air systems, and radiators for hot water systems, are placed near windows and doors. It keeps the windows warmer and above the dew point and also makes the air warm from your heat loss near these locations.
Lennox G61MP Gas Furnace
The furnace you describe, the Lennox G61MP, is a condensing furnace and having the combustion air intake in the basement actually contributes to removing humidity from the basement. It sucks the air from the basement for use in the combustion process and the humidity in this air is condensed during the combustion process in the heat exchanger. This condensation is gotten rid of down a condensation drain near the furnace or blown out the exhaust where the combustion gases are expelled. If your supply vents are located near the doors and windows and you still have this problem then it may be time for new doors and windows as you have too much heat loss at these places and all the humidity is being condensed around the windows in your home.
Hello and Thank you for emailing High Performance HVAC, Dorothy, Your registers should not be closed off as it is bad for the unit. The unit was installed based on the size of your home and the needed airflow for the house. This is designed airflow and requires all registers to be open to get the designed airflow through the unit and all the ducts. Closing off registers restricts airflow and is the same as a dirty filter which restricts airflow and causes problems with the unit. I have seen this before and I cover this on the 
Richard Many thanks for your very prompt response! What you say ties in with what I read regarding stress on the unit. However, this Victorian “cottage” is 3,000 sq. ft. w/ 12 ft. ceilings is now too big for only my husband and I. Is there not a way we can isolate the unused space and save on heating without stressing the unit? We have done all that you suggested. Storm windows, doors, etc., except for the attic insulation. The company that installed the unit is no longer in business and the man that I got to service it after that died. last fall. I’m in a very small town and the nearest Heil dealers seem to be 40 or more miles away. I did print a list of those I found. Haven’t called any yet as I ran across your webpage. My final question is, given the size of the unit, could I convert to 2 zones somehow? And, only heat the occupied part in winter? Thanks for you patience and help.
