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High humidity in house

Hello. I have a 1000 sq ft steam heated ranch house that was built in 1952 in Massachusetts.  The heating system is a one-pipe steam radiator system with a boiler that is approximately 10 years old (Burnham Independence Gas-Fired Boiler). In 2010, we had our house insulated with blown in cellulose and soon after we noticed that the 20+ year old replacement windows would get extremely wet on the inside and mold was growing on the window sills. We have replaced all but two of the windows with new replacement ones in 2012 and thought that would solve the problem.  Unfortunately, it hasn't.

This winter, we've noticed that the humidity is very high and we are wondering if the house is now "too tight" preventing moisture from esaping.  I am running a dehumidifer that we normally run in the basement during the summer and seems to taking some of the moisture away, however it doesn;t run all the time and I really don;t want it to.

Any suggestions/diagnoses is appreciated.  Thanks!


  • BillW
    BillW Member Posts: 198
    1. Every time you take a shower, boil a pot of pasta, or hang wet laundry to dry, you add humidity.  If you are getting excessive condensation on your windows, to the point where you get drops and wet windowsills, you do have a humidity issue. A HEAT recovery ventilator (HRV), NOT an ENERGY recovery ventilator (ERV) may be of help; they tend to dry a space as they increase ventilation, they need a drain, and must be mounted in a conditioned space, since they contain liquid water at some point, and can freeze. They also require some insulated ductwork, and must be sized to work properly.  Is your basement wet? Does it have a dirt floor and a rubblestone wall?  Any leaks in the roof or siding?
    Optimum levels of humidity are between 40-60%.  Below 40%, you can get static electricity problems, dry nasal & bronchial passages, cracking woodwork, or cupping or shrinking of wooden flooring or trim.  Above 60%, condensation and possible water damage to windowsills and the potential for mold growth are concerns.  Find out what your humidity levels are, and if they are above 60%, take steps to reduce the level.  HRV's are not a do-it-yourself project, you need a pro. I hope this is helpful.
  • Jonathan_17
    Jonathan_17 Member Posts: 5
    RE: Humidity

    BillW - Thanks for your reply.  My house does not have a dirt floor or rubble stone walls (I have concrete walls and floor).  There are no leaks in the roof or siding either. When I start my dehumidifier, the humidity reader on it typically reads 80-85%, however after letting it run for 20-25 minutes, it drops to 50-55% and then I usually run the dehumidifier for at least one hour after that.  I have been doing this 2-3 times per day for the last four days and it seems to be helping, but is not a permanent cure.

    Since your post, I’ve looked up HRVs on Google and they look pretty expensive. There is no question that a pro installer is needed too.  Are these installed by HRV specialists, or by general HVAC contractors? Can they be installed independently from my steam heating system, or would I have to change my heating system to another type (e.g. force hot water or forced hot air)?
  • BillW
    BillW Member Posts: 198

    You don't need to change your heating system to install an HRV.  They need some duct work, however, and it has to be insulated.  The HRV has an outside air intake, which must be located above the snow line, away from any odor sources like car ports, dryer or heating equipment exhaust, trash cans or pet areas.  The HRV needs to be in a conditioned space, so it can defrost as needed, and have a drain to get rid of the water.  The discharges are located high up on the wall, so that they won't blow on anyone directly, since the HRV is only about 80% efficient, you can get some chilly air out of them on extremely cold days.  One central intake for the indoor air is usually sufficient, and is often located near the bathroom to help exhaust shower steam and odors.  Controls can be a de-humidistat, a timer, or a thermostat with an HRV option.  Some HRV's have filters that need to be replaced regularly, others have Ultraviolet lights to minimize airborne germs, and those also  need periodic replacement, as the bulbs degrade over time.  HRV's are run on low speed all the time, and can be speeded up as needed to dilute and exhaust odors and excess humidity.  Any competent HVAC contractor can install one of them for you, but one who has experience with more advanced systems is the best choice. Try the "find-a-contractor" feature on this website. I don't recommend specific brands, but there are many out there, and they all work the same way.
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