How to Heat Under a Skirted RV: Choosing the Right Heater for Winter Freeze Protection

RV skirting can make a major difference when camping, storing, or living in an RV through the winter. By blocking wind and creating an enclosed space beneath the RV, skirting gives you an opportunity to protect freshwater lines, tanks, valves, pumps, drains, and other vulnerable equipment from freezing.

But putting skirting around an RV does not automatically make the space freeze-proof. When temperatures drop into the single digits or below 0°F, adding a reliable source of freeze protection becomes especially important.

The question we hear is:

There is no single answer based only on RV length. The correct heater setup depends on the size of the space, the type of skirting, how tightly the skirting is sealed, its insulation value, wind exposure, the equipment you actually need to protect, and the lowest temperatures you expect to encounter.

If you just want the short version, a 600W heater is a good starting point for smaller, well-sealed skirted RVs, around 20ft or smaller.  An 800W heater is generally our starting point for larger skirted RVs  (up to 35ft) that may see temperatures into the single digits.

If a single 800W heater is close but you want additional capacity for peace of mind while staying with one heater, our 1000W RV heater can be a good option.

For long RVs, less insulated skirting, windy locations, or temperatures that regularly drop close too or below 0°F, we generally recommend a twin-heater configuration using two 600W or two 800W heaters. In addition to providing more total heating capacity, using two heaters at opposite ends of the RV can provide much better air circulation.

Use the chart below as a starting point, then read the rest of the article to understand how skirting, insulation, airflow, heater placement, and the amount of space you are actually trying to protect can change these recommendations.

These are starting points, not an absolute sizing formula. A well-sealed RV with rigid foam skirting can require significantly less heater capacity than the same RV surrounded by thin skirting with gaps and heavy wind exposure.

The heater is only one part of the system. Your skirting determines how easily the warmth produced by the heater can be retained.

A basic vinyl or fabric skirt can do a good job of blocking wind, but it generally provides much less insulation than rigid foam board or an insulated skirting system. If there are large gaps around the ground, corners, slides, stairs, utility connections, or other openings, warm air can escape while extremely cold outside air enters.

The tighter and better insulated the skirted area is, the less heater capacity you will generally need to keep that space above freezing.

Think about three things when evaluating your skirting:

Air leakage: Look for gaps where wind can enter. In very cold weather, moving cold air can make maintaining temperatures much more difficult.

Insulation: Rigid foam or insulated skirting retains warmth much better than a thin wind barrier alone.

Exposure: An RV sitting in an open, windy site will usually require more freeze protection than the same RV protected by trees, another structure, or a covered site. Before simply adding more heater capacity, it is often worth asking whether you can improve the skirting itself.

One of the best ways to improve efficiency is to reduce the amount of space you are trying to protect.

A skirted 40-foot fifth wheel can create a surprisingly large volume of air underneath the RV. In many cases, however, the entire space does not necessarily need to be kept warm. The real objective is protecting specific plumbing and equipment from freezing.

If your freshwater lines, tanks, valves, pumps, filters, or other vulnerable components are concentrated in one portion of the RV, consider building a smaller protected area around them. Rigid foam board can be used to create insulated walls or partitions under the RV. Instead of trying to maintain above-freezing temperatures throughout the entire footprint of the RV, you may be able to create a much smaller protected enclosure around the equipment that matters.  

Reducing the volume of air that needs to be heated can allow you to use a smaller heater, fewer heaters, or provide more reserve heating capacity for the coldest nights.

Keep enough open space around the heater for unrestricted airflow. The objective is to create a smaller insulated zone, not to tightly box the heater in.

Heater position can also make a noticeable difference. When a heater sits directly on frozen ground, concrete, gravel, or another extremely cold surface, a portion of the warm discharge air travels directly across that cold surface. Instead, place the heater on a stable wood block, cinder block, or similar raised platform. Getting the heater several inches off the ground allows the warm discharge air to enter the space more effectively rather than immediately sweeping across one of the coldest surfaces in the enclosure. It is a simple adjustment, but when you are trying to maintain temperatures above freezing during a severe cold snap or simply save a bit of electricity, small efficiency improvements add up.

Avoid placing the heater directly against the skirting. As a general starting point, place the heater a few feet away from the skirting wall whenever the available space allows it. You want the heater moving air throughout the enclosed area, not simply blowing warm air directly into the skirting. The same applies to the rear of the heater. The thermostat is located on the back of the Xtreme Heater. Proper air circulation allows the heater to sense the temperature of the space more accurately and cycle normally. If it is too close to the skirting, it could be reading a colder temperature than it would in the circulating pool of air.

Our thermostatically controlled RV heaters turn on at approximately 40°F and off at approximately 55°F, with a tolerance of ±3°F. If warm air never circulates back through the space, the area around vulnerable plumbing may be warm while the thermostat remains in a colder pocket. Good circulation helps the heater respond to the overall environment rather than only the conditions immediately surrounding it.

For larger skirted RVs, two heaters offer another important advantage: air distribution.

A long fifth wheel or motorhome can be difficult to heat evenly from one location. You may have plenty of warmth near the heater while the opposite end of the RV remains much colder.

When using two heaters, position them on opposite sides and opposite ends of the skirted area. Aim each heater generally toward the opposite end of the RV so that the two heaters encourage a circular or counterflow pattern.

A typical arrangement looks like this from above:

Our 1000W RV & Camper Heater is useful for applications that fall between a typical single 800W installation and a twin-heater setup. For example, you may have a well-insulated skirted RV where an 800W heater is almost sufficient, but particularly cold nights leave you with less temperature margin than you would like. Moving to a single 1000W heater provides additional capacity without changing to a two-heater installation. The 1000W can also make sense where the heated area is relatively compact but the expected temperature is unusually low. However, a 1000W heater does not eliminate the airflow advantages of using two heaters in a long RV.

If your issue is that the front of the RV stays warm while the far end gets too cold, a second heater placed at the opposite end may solve the problem better than simply adding more wattage at the original location. Think about whether your issue is not enough total heating capacity or not enough circulation.  

We generally do not recommend using two 1000W heaters together unless you have confirmed that the available electrical system can support the combined 2,000W load. If that much capacity is needed, verify the available circuits and electrical capacity rather than assuming the existing RV connection can support both heaters.

We have also tested this concept with customers in real-world winter conditions.

One particularly useful example involved a 42-foot Travel Supreme fifth wheel in West Branch, Michigan. The RV was skirted with foam board and also had some overhead protection from a carport structure.

We originally planned to use two large Xtreme Heaters. We asked the customer to begin with one 800W heater and add the second heater if temperatures underneath the RV started getting too close to freezing. Temperature sensors were positioned at three locations underneath the RV to see how well the warm air was circulating.

During one documented 24-hour period, the outside temperature reached a low of 8°F.  Even with only one 800W heater operating, all three sensors remained above freezing. The coldest reading was 34°F at the sensor located farthest from the heater. This is an excellent real-world example of what can be accomplished with good foam-board skirting and an Xtreme Heater.  

It is also important not to overstate the result. The site's data connection was lost during the later portion of the winter when temperatures dropped well below 0°F, so we do not have complete recorded data from the coldest period.  We added a second heater before hand resulting in the entire area remaining above freezing while well under 0F outside

If you want to see the test setup, sensor locations, temperature data, and the results in more detail, read our full case study:

If the coldest winter nights in your area occasionally fall into the single digits, a well-sealed and insulated skirted RV may perform very well with one 800W Xtreme Heater, particularly if the space is not excessively large and airflow is good. If a single 800W heater is close to meeting the needs of the installation but you want some additional capacity, the 1000W model is another single-heater option.

Once temperatures regularly fall below 0°F, we recommend becoming more conservative.

This is where our twin-heater configurations become particularly useful. A Twin 600W setup may be appropriate for a well-sealed, well-insulated RV where the space is reasonably sized and the primary goal is adding capacity and improving circulation. For larger fifth wheels and motorhomes, less insulated skirting, greater exposure, or more severe below-zero conditions, the Twin 800W setup gives you additional reserve capacity while still providing the circulation benefits of having heaters at opposite ends of the RV. If temperatures can fall well below 0°F for extended periods, the quality of your skirting becomes even more important. Adding heater wattage without addressing large gaps, poor insulation, or unnecessary heated volume is usually not the most efficient approach.

Another lesson from our Michigan test is the value of using multiple temperature sensors.

A thermometer sitting next to the heater does not tell you what is happening 20 or 30 feet away around a water line, valve, holding tank, or outside corner.

Consider placing remote temperature sensors:

Do not place every sensor directly in the heater's discharge airflow. You want to know the actual temperature in the protected area, especially at the locations most likely to become cold.

Monitoring also allows you to evaluate your system before the worst weather arrives.

For example, if the coldest sensor underneath your RV is already approaching freezing when the outside temperature is 15°F, you know you have very little reserve capacity for a night expected to reach 0°F.

That gives you an opportunity to seal leaks, add insulation, modify heater placement, improve circulation, reduce the heated volume, or add another heater before the temperature falls further.

For the best freeze protection under a skirted RV, think about the complete system.

Keep the cold air out. Seal gaps and improve the skirting wherever possible.

Keep the warmth in. Higher-insulation skirting or rigid foam board reduces heat loss.

Reduce the area you need to protect. Build insulated partitions around plumbing and equipment when practical.

Raise the heater off the ground. A wood block or cinder block can improve the way warm air enters and circulates through the space.

Give the heater room to circulate air. Keep it a few feet away from the skirting walls where possible.

Use multiple heaters strategically. On long RVs, place two heaters on opposite sides and opposite ends and aim them in opposite directions to encourage circulation throughout the enclosure.

Remember where the thermostat is located. The thermostat is on the rear of the heater, so proper circulation around the heater helps it accurately respond to conditions underneath the RV.

Monitor the cold spots. Remote temperature sensors can tell you whether the areas farthest from the heater are actually staying above freezing.

The objective is not to make the area under your RV comfortable. The objective is to efficiently maintain temperatures above freezing around the systems that need protection.

If you only experience occasional freezing conditions and have a relatively small, tightly skirted area, you may need much less heater capacity than someone living through a northern winter with extended below-zero temperatures.

For skirted RV applications, the primary Xtreme Heater options are:

For smaller equipment compartments or insulated zones that you create under the RV, the 250W Enclosure Heater and 400W RV & Camper Heater may also be appropriate.

Before simply moving to the largest heater possible, look at the entire installation. Improving your skirting, sealing air leaks, reducing the heated volume, raising the heater off the ground, and improving circulation can sometimes accomplish more than adding wattage alone.

Every RV and winter environment is different. If you are unsure which heater or combination of heaters is appropriate, contact Xtreme Heaters with your RV size, type of skirting, expected minimum temperature, location, and the equipment you need to protect. We can help you determine a practical starting point for your installation.