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Reducing furnace blower noise

We installed recently a new heating system that allows us to heat the house more cost and energy efficient. The electric meter sends a signal to the heating system indicating the cost of the electricity. The heating control system can then make the best choice between 3 different sources of heat (heat pump, pure electic heat strips and oil).

We were all quite excited about it since the previous system was very old and we would now have something that is much better. Part of the installation was a KLR-200 oil furnace made by Granby Industries. It's a small high efficiency hot air furnace but it has a rather loud air blower. We could not believe that this was a new heating system. It was so loud, especially in the rooms next to the furnace room.

I googled "loud air furnace", "furnace blower sound" and other terms to see what other people are saying and it seem that nobody had a good solution to completely get rid of the blower noise.

Adding more return air ducts

If you hear a high frequency whistle tone from your blower that goes away when you open the blower air filter door then that is an indication of insufficient return air. A stronger blower wants to move more air and to do this is needs to suck-in more air. If it can only do this by generating a stronger vacuum on the air intake side then this can make the blower noisy. The blower should just push the air through the system is should not need to generate a vacuum on the intake side or high pressure on the blower output side.

It's a duct dimensioning problem if the pressure difference is high. So check first for obstructed or too small air ducts especially return air ducts. If you are sure that those are good then proceed further.

Building an air furnace sound insulation

Magic eraser sponges are made of an open cell melamine foam. Melamine foam is very heat resistant and does not burn. It was originally designed to be used as an acousting foam for sound damping purposes and people discovered only later its cleaning properties.

open cell melamine foam aka magic eraser spong

My idea was to install that foam inside the furance right next to the blower intake. For this I made a sandwich out of a galvanized steel sheet the foam and a wire mesh. The wire mesh would be connected with steel wires to the steel sheet and secure the foam such that it could not be sucked into the blower.

It worked very well and reduced the blower noise significantly. Here is how to do it.

I started with the galvanized steel sheet and I cut a piece large enough to cover a wall of the furnace blower chamber.

A rol of thin galvanized steel

galvanized steel sheet cut to the right size

I "painted" one side of the steel sheet with contact glue and stuck enough magic eraser foam pieces to the sheet to cover it. I used the extra strong version of magic eraser foam because it is more dense and has a lower profile.

magic eraser sponge as acoustic foam glued to the steel sheet

I was afraid that some foam might loosen eventually and then get sucked into the blower. To make it extra save I put a piece of chicken wire on top of the foam and then I drilled some holes throug the sponge and the steel sheet. I used then steel wire to connect the chicken wire to the steel sheet on the back. It made a very strong sound absorbing sandwich which I screewd to the side wall of the furnace blower chamber.

A much more silent hot air furnace

This is a view of the open furnace blower chamber and the sound damping sandwich out of melamine foam is installed right next to the blower.

Sound damping melamine installed right besides the blower in the furnace

This had a noticeable sound reduction effect since it cuts the noise right where it originates.

I used to measure in the furnace room at a distance of 1m from the blower door 62dBA and after installing this foam it went down to 58dBA. In the room above the furnace room I used to measure 33dBA (noticeable noise) at a distance of of 1m from one of the return air intakes and now I measure 28dBA (not noticeable). I can recommend this system to reduce the noise further but you should first check that your furnace has as much unrestricted air flow as possible. A too small opening for the return air is the number one cause of blower noise.

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