MLive
mlive.com › home_improvement › 2007 › 10 › ventless_propane_wall_heater_c.html
Ventless propane wall heater causes moisture - mlive.com
October 28, 2007 - These places get and stay cold, giving the warm, moisture-laden air an ideal place to condense when it floats into the vicinity. If the unvented gas heaters are creating intractable problems due to the amount of water vapor they produce, the only solution - other than running the dehumidifier as you've been doing - is to get rid of them.
Protimeter
blog.protimeter.com › blog › preventing-indoor-cold-weather-condensation-dampness
Condensation Dampness: Assessing Winter Moisture Issues | Protimeter
However, they may not be aware of the potential dangers of overusing this alternative heating source. Problems arise when unvented propane heaters cause condensation, and condensation causes mold and mildew.
Published October 20, 2025
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vent free gas heaters and Dehumidifiers - YouTube
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The Money Pit
moneypit.com › home › general › ventless natural gas heater moisture problem
Ventless Natural Gas Heater Moisture Problem » The Money Pit
January 17, 2023 - A dehumidifier will remove the moisture, but keep in mind that the other combustion byproducts will saturate the room. For example, should the gas burners malfunction, they could produce a toxic level of carbon monoxide. If you keep using this ventless fireplace (which I do not recommend) I’d also recommend installing a plug-in carbon monoxide detector. ... Tim’s reply is right on. Use a dehumidifier. That will solve the problem.
Chevy Tri Five Forum
trifive.com › home › forums › chevy trifive forums › garages bodyshop or work area
Garage Heater Issue | Chevy Tri Five Forum
Anyone want to buy a slightly used ventless gas heater? ... I recently installed a natural gas vent-less garage heater. Works great except it produces a lot of humidity. It makes the windows very wet and the single pane glass on the garage doors freeze up. However, I got really concerned while working under the car with the heater keeping the garage at 55* running. The underside of the car was wet with moisture...
Reddit
reddit.com › r/hvacadvice › question about using ventless ng heater and dehumidifier in garage: is this a counterproductive way to counteract moisture?
r/hvacadvice on Reddit: Question about using Ventless NG heater and Dehumidifier in garage: is this a counterproductive way to counteract moisture?
April 28, 2025 -
Our house came with a ventless natural gas heater in the garage already hooked up. I know that moisture is an issue, so before I run it next winter, I am considering setting up a dehumidifier in the garage to counteract the moisture problem.
I've seen repeated multiple people in multiple places online saying that using a ventless natural gas heater and a humidifier in the same place is silly. Many people say that with the electricity use from the dehumidifier, "you may as well just use electric heat."
But this doesn't make sense to me. A standard dehumidifier unit uses a few hundred watts, and increases sensible heat. In fact if a dehumidifier uses say 300W of electricity, it can produce sensible heat by about 1100W, through the conversion of latent heat in the moisture. That's about 3700 btus in extra heat output, from only 300W of electricity. Also, dehumidification will almost match the moisture output of an 18000 btu ventless natural gas heater.
Meanwhile you would need multiple 1500W electric heaters to match the heat output of a ventless gas heater. So with natural gas being substantially cheaper per btu than electricity, it seems like a dehumidifier would help mitigate the moisture problem of a ventless heater, with minimal downside over just using electric.
All of this of course, requires enough ventilation in the garage to restock oxygen for the heater, which would be supplied in this case by slight gaps around the garage door, and the daily opening and closing of the garage door to get a car in and out.
A carbon monoxide detector would be used to avoid dangerous CO levels.
Someone tell me why this is a bad idea? My *albeit limited* understanding of heating suggests that a dehumidifier could counteract the most significant negative effect of a ventless heater, with minimal negative side effects.
Airpurelife
airpurelife.com › ventless-heater-moisture-problems
Ventless Heater Moisture Problems [Possible Reasons & Solution]
January 28, 2023 - It’ll be wise to simply partially ... result, you should consider installing a dehumidifier. A dehumidifier will help to reduce the moisture created by the ventless heater without distorting the heat in the room....
Hero Plumbing
heroplumbing.com.au › home › do ventless heaters create moisture
Do ventless heaters create moisture - Hero Plumbing
Hero Plumbing Services
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Reddit
reddit.com › r/hvacadvice › ng wall heater
r/hvacadvice on Reddit: NG wall heater
April 22, 2021 -
hello, i have a 18000 btu blue flame wall heater in my small work shop, i get surface rust on my equipment and couldnt figure out why since the humidity isnt that bad out there. i was reading that it could be caused by the heater ?
Top answer 1 of 6
2
If you quickly heat up the air around cold metal, you get condensation. Water will rust metal.
2 of 6
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That is a ventless heater, so yes all the moisture from combustion is going into the space and raising the humidity in the shop. Humidity would get especially high when the room cools down after using the unit, likely to the point of condensation in a cold climate. Try to replace it with a vented model. Could add a constant low speed exhaust fan to help remove the humidity. Avoiding large temp swings will also help avoid surface rust.
BuildingGreen
buildinggreen.com › blog › avoid-unvented-gas-heaters
Avoid Unvented Gas Heaters | BuildingGreen
June 13, 2016 - This moisture can result in mold growth, induce allergies and asthma among homeowners, and cause rot. The tighter the house, the greater the risk. A 30,000 Btu/hour unvented gas heater will produce about a third of a gallon of water per hour--about seven gallons per day if operated around the clock.
Fairviewhearthside
fairviewhearthside.com › research-on-how-vent-free-appliances-affect-indoor-humidity8ad2644f
Research on How Vent-Free Appliances Affect Indoor Humidity
July 17, 2025 - A beneficial and comfortable level ... home because they do not require a vent to the outside. They are 99% efficient and do not add significant amounts of moisture to the air in most cases....
Quora
quora.com › What-are-the-pro-con-of-using-a-ventless-propane-heater-I-heard-it-pumps-out-water-vapor-we-use-2-gal-day-to-humidify-the-house
What are the pro/con of using a ventless propane heater? I heard it pumps out water vapor (we use 2 gal/day to humidify the house). - Quora
Con: Supplies water vapor which can cause mold and a lot of other problems. Con: Produces carbon monoxide, which can kill your entire family. Low humidity is caused by too much cold air leaking into your home. Cold air cannot hold much moisture, ...
Greenhousemag
greenhousemag.com › article › unvented-heaters-spell-trouble
Greenhousemag
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Todd Miller
asktoddmiller.com › home › roofing information › ventless gas stoves and condensation
Ventless Gas Stoves and Condensation - Todd Miller
February 13, 2011 - However, as you introduce heat to this room and potentially moisture / humidity from the rest of the house filters into this room, there is indeed increased risk, probably significant, that warm moist air inside the room, will connect with the inside of your cold roof and wall surfaces, and condense there. You might get by with running a dehumidifier in the room. On the other hand, that may not be enough either. ... I also have a ventless gas stove in my 4 season sunroom.
Sawmill Creek
sawmillcreek.org › forums › woodworking topics › workshops
Vent Free Propane or Natural Gas Heater | Sawmill Creek Woodworking Community
November 3, 2018 - Avoid them like the plague unless your shop is basically wide open and leaky. Natural gas ventless heaters will produce nearly 100% moisture when they are running.
Carbonmonoxidemyths
carbonmonoxidemyths.com › myths › myth-9
Vent-Free Propane Heaters: Safety Myths Debunked – Carbon Monoxide Myths
July 10, 2024 - Critics of these heaters suggest that the moisture output from vent-free units can lead to increased humidity inside homes, fostering conditions suitable for mold and mildew growth, which can compromise structural integrity and resident health.
Small Cabin Forum
small-cabin.com › forum › 3_9533_0.html
Ventless Propane Heaters - Small Cabin Forum (1)
Cabin Forum/Blog: Just a question for all of you out there that have a ventless propane wall heater. Are they safe? Are you placing a vent below and above it for fresh air from the outside?
TractorByNet
tractorbynet.com › forums › community forums › rural living
Any one use a ventless gas stove for heating.??? - TractorByNet
January 16, 2016 - It should be up to the job of keeping you warm. The ventless wall heaters are no different than your wife turning on a burner in the kitchen. Same principle... They are about the most efficient way to heat with gas, but create moisture problems if you run them a lot.
Reddit
reddit.com › r/tinyhouses › how safe are we heating our 250sqft house with ventless natural gas?
r/TinyHouses on Reddit: How safe are we heating our 250sqft house with ventless natural gas?
January 12, 2020 - The added moisture isn't necessarily a plus. Humidity buildup, condensation, and the resulting mold are a big problem in tiny spaces. ... I didn't die and it sure kept the single-room apartment toasty.
The Garage Journal
garagejournal.com › forums › the garage › heating and a/c
dehumidifier for ventless gas heat | The Garage Journal
January 4, 2014 - Heater 30k BTU ventless in about a 600 SF garage, very well insulated. Dave ... I would suppose a dehumidifier would work in that situation, but I have no practical experience. Perhaps others will chime in... Dave · To avoid these ads, REGISTER NOW! ... Your friend needs to ventilate the space and/or use it less. Vent free heaters are designed and approved as supplemental heating devices.
ECOJOHN
wildoaktrail.com › home › off grid living
Direct Vent Propane Heater vs. Ventless Heater: Which One Should You P - Wild Oak Trail
February 13, 2024 - Condensation can form on your home's windows or doors as a result of this. The increased humidity can cause problems with wooden items like floors and doorways, so if you don't keep an eye on it, this could lead to mold or mildew in your house.