Should Crawl Space Vents Be Open or Closed in Winter?

Having a crawl space underneath the house can be really convenient. It is cost-effective as well as space-saving. One would not need to worry about where to put the pipings and sewage distribution. One can always hide them in the crawl space. And the repairing gets easier as well. The house can also be sustained for a longer time, as the possibility of getting damped is lower with a crawl space.

But the real concern with crawl space arises with whether it should be left open or closed. Letting a crawl space fully open might not be one of the smartest ideas, but keeping a vent or two is supposed to be fine, provided it has an accessible easy-on-and-off sealing like Historically, it has been said that having crawl space vents is more or less equivalent to having windows in the house. It serves as a ventilator and helps circulate outside air into it, keeping the humidity balanced inside the closed space during summer. However, it also increases the chance of equipment being frozen in winter. Then, what should one do?

To answer this question, let us inspect the matter a bit closer.

What Are The Disadvantages Of Crawl Space Vents?

Although vents are a viable solution to maintain humidity levels inside the crawl space, they can also be quite problematic.

Low Heating Efficiency:


Keeping crawl space vents open in the winter will surely make the heater less efficient. No matter how good the heater is, cold air from outside will keep coming in under the house, making the air chillier than usual.

Frozen Equipment:

Another downside of open vents is the possibility of the equipment being frozen. During winter, equipment such as pipelines and sewer systems can freeze and be permanently damaged if the temperature drops well below the freezing point.

Condensation Effect:

If the crawl space is not cleaned or managed properly, the open vents might cause condensation on the foundation and other equipment stored there.

Attractive Nesting Place:

Crawl spaces have always been an attractive nesting place for many animals, bacteria and fungoes. An open crawl space vent might increase the probability of one’s foundation space being used as a nest.

Creaking Floor:


Open vents do not just allow air into the crawl space but also bring dust particles, molds, and pollutants into the air. Not just that but moisture and mold will keep building up, damping the wooden joists. Over the years, these particles, along with bacteria and molds, can cause harm to the foundation woods, resulting in weak rims, beams, and creaking floors.

Damaged Insulation:

Cold air and snow can damage insulators permanently. If the house insulating system is installed in the crawl space and the vents are kept open during winter, there is a high chance that the insulator will not work properly. The moisture from the melted snow and air will destroy the entire insulating system from the core.

Should Crawl Space Vents Be Closed Permanently?

This is a much-debated question. Although traditional house builders are in favor of keeping vents in foundation space, many architects and scientists these days are opting not to build any vents in the crawl space. Some are even going for sealed-off vents. But according to most builders, it solely depends on the soil, weather and pollution level of where the house is situated.


If the house is situated somewhere in extreme cold r humid weather, it is best to seal off the vent and insulate the crawl space properly to get the best outcome and maximum sustainability. However, if the house is being built in a less humid zone, it is okay to keep open vents. But one should make sure to get a lid to close them off in winter.

However, it has been tested that closed-off crawl space stays drier than open-vented ones, regardless of the zonal weather and seasons. But provided that the crawl space is properly insulated.

How To Close Off Crawl Space Vents?

There are multiple ways to seal off a vent located in the crawl space.

Plugging In Foam Blocks:

This is one of the easiest and most popular ways to close off vents. One can measure the size of the vents, go to the market and get the sealing foams specifically made for this purpose. These foams are easily available and do not cost must. Once bought, plug them in the vents from outside, and these are good to go.


Air-sealing The Vents:

Another way to seal the vents is to buy air-tight vapor barriers from the market and seal the vents using them inside and outside the crawl space. These seals would isolate the crawl space from the open air. One should make sure not to leave open any hole or creak during the process. Otherwise, the barriers would not work.

Other Ways To Solve Open Vent Problems

There are a few ways to solve the above-mentioned problem without sealing off the vent. Although the ideas are not full-proof, if one does not want to close off the vents, he can opt for it.

Install a Dehumidifier:

An easy way to control humidity inside the foundation space and prevent moisture from building is to install a dehumidifier. This would keep the humidity level in check during summer, though it may not be very feasible for winter.

Insulating The Crawl Space:

One can try insulating the crawl space to avoid potential problems from occurring. But the space needs to be cleaned, checked and maintained regularly. Moisture and condensation can damage the system.

Concluding Thoughts

One should always keep in mind that crawl space is the foundation base of the home. The pros and cons of foundation space vents are all mentioned here. So, the next time someone wants to build a new home or buy one, make sure to go through them carefully, understand the respective advantages and disadvantages, possible solutions and consult your builder or contractor before purchasing it.