ERV vs Dehumidifier vs Alternatives in Tiny Home

Hello all. I’ve got a tiny house on wheels located near Nelson, BC, and it has frequent moisture problems. I’m trying to determine the best course of action to resolve the moisture/high humidity and mold problems that have been recurring.
An ERV was recommended to me by a repairman that dealt with some mold repairs in the winter of 2023/24. I did not add an ERV at the time, opting instead for a small dehumidifier and better monitoring of the problem areas. I’ve discovered that I have mold again growing in a hidden spot behind my couch, and the bathroom clearly has an excess of moisture, as the T+G panels have swelled and bowed in a couple of spots.
I thought that the ERV was a good solution, however in my reading it seems like it might not be suited for my situation. Winter tends to be when the indoor humidity is highest, averaging in the mid-60% RH range from Nov 2024-Jan 2025. Summer ranges are lower, in the mid-50% range, but still quite high. There is significant condensation on the insides of the windows throughout the winter.
I also considered a dehumidifier with a bigger capacity, but I’m not sure that would be enough to solve the problem entirely either, given the lack of ventilation in the house. A contributing factor may be that some window condensation drips down behind the couch to a corner that is somewhat tucked away. However, I am working off the assumption that the heavy dripping condensation is a symptom of a different problem, rather than the sole cause of my mold issue.
Aside from the mini-split and bathroom exhaust, there isn’t any dedicated ventilation for the house.
The house is approx 200 square feet, built in 2021 and insulated with spray foam. Nelson is in Climate Zone 5 (Canadian version) with 3000-3999 HDD.
Currently considering the following options:
– install ERV
or
– install/add dehumidifier with larger capacity or dedicated drain line
Appreciate any and all suggestions as to how to mitigate/eliminate the problem of high humidity and mold growth.
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Replies
I don't have any experience with ERVs but I have used dehumidifiers in small spaces. They work great, with the added benefit of throwing a decent amount of (very dry!) heat. Amd they're not that expensive. Try a bigger unit and see how it does.
johnny,
The problem with relying on a dehumidifier is you still are left with needing a source of ventilation for interior air quality. You can use your existing bathroom fan run periodically, or just open a window, but an HRV will solve both the high humidity and improve IAQ, without losing a lot of heat.
Your indoor RH is very high for wintertime in Canada. That is almost always the result of inadequate ventilation. Cold outside air is dry, so exhausting moist indoor air and bringing in fresh air will make your interior air much drier.
The BC Building Code requires that a small one-bedroom home have a ventilation system capable of bringing in 14 liters/second of fresh air continuously. If you don't ventilate enough, you will have very poor air quality with high levels of CO2, formaldehyde and other VOCs, airborne chemicals from cleaning products, smoke particles from cooking, combustion byproducts if cooking with gas, etc. A dehumidifier doesn't remove any of those. Minisplits also don't ventilate.
An inexpensive fix for your problem would be to install a timer that automatically runs your bath fan for about 30 minutes every hour. A typical bath fan exhausts about 30 l/s, so running it 30 minutes per hour will be roughly equivalent to the code requirement. You could also get an indoor air quality monitor. If it shows that indoor pollutants are still higher than recommended, increase the fan run time. If pollutants are within recommended safe levels, you could try dialing it back a bit.
If you decide to go for an ERV or HRV, just be aware that a single Lunos system is usually not enough.