Have you ever cursed your RV furnace for waking you up in the middle of the night? Have you ever had to turn up the TV a few notches when the heater kicks on? RV furnaces are notoriously noisy for a number of reasons. Generally, most of the noise comes from the high-speed fan which is then amplified by the enclosure the furnace sits in. This how-to focuses on how to reduce the furnace noise using soundproofing material and a little airflow trick that will lower the noise level to a dull roar.
Step 1: Measuring enclosure
Start by removing the air return register and inspecting the inside of the furnace enclosure. With a tape measure, measure the dimensions of the top, back, and sides of the enclosure. For example, the top of the enclosure may measure 24″ x 24″. Tha’s 2′ x 2′, or 4 sq. ft. What you are doing is measuring the total square footage of the enclosure interior where you will be placing the soundproofing material. Typically, about 6-8 sq. ft. is required, unless you have a really big enclosure, like the inside of a dinette bottom storage area.
Step 2: Determine airflow requirements
Now get out your furnace manual. Find out how many square inches of return air area the furnace requires to operate effectively. For example, a 30,000 BTU Suburban furnace requires 54 sq. in. of opening area for the air to flow through the return grill. This size furnace usually will have a grill that has 4 sets of louvers. Only 2 are actually required to support the return air requirement, which in this case is about 60 sq. in.
Step 3: Adding soundproofing material to register
Next, add some soundproofing material to the back of the register. Much of the blower noise is transmitted through the front of the register, so it makes sense to try and reduce noise here as well. In the example in step 2, you should apply soundproofing material on the back of the register over the middle two of the four louver columns. This is OK to do since you are still meeting the return air requirements of the furnace.
Step 4: Adding soundproofing to the enclosure
Cut the soundproofing material to fit your measurements of the furnace enclosure and affix to the walls (sides, top, and back) of the enclosure. The material suggested in the parts source link below can be had with a peel-and-stick backing, making the attachment of the material very easy. It costs a little more than the non-sticky stuff, but you won’t have to use any glue if you choose this type.
Step 5: Install return grill
Re-attach the return air grill and turn on the furnace. Let the furnace run through a complete cycle to ensure everything is working properly.
Tips and warnings:
- You can expect a reduction of about 6dB of noise level. How much is this? The human ear perceives sound levels of 3 dB as being twice as loud or quiet. For example, if you measure your furnace noise output, it might be 61 dB at 5′. Reducing the noise level to 58 dB would be perceived as twice as quiet. With this mod, using the 3/4″ material, your furnace could be a much as four times as quiet! Now you won’t have to turn up the TV every time the furnace kicks on!
- Ensure that you provide adequate air flow through the return air grill by adhering to your furnace’s minimum air flow requirements specified in the owner’s manual. Otherwise, the furnace may perform erratically or shut down due to overheating.
