DwyerLiquid Filled Wall Mount Manometer, Mark II 25, 0-3" w.c., 3% Accuracy

This is a good looking, solidly built lab instrument that I use to know when to change my HVAC air filter. In my 20X30X1 inch filter I get a reading of 0.3 inches of water column with a MERV 18 filter when it is new. The gauge comes with everything you need to install it. Be careful when adding the red fluid it only takes a little. The bottle that comes with the gauge is 20 times more than you need. I over filled it initially and used a pipe cleaner in the fill hole to easily remove the excess fluid. I may buy another one for my other AC/Heater.

New furnace went in with a new (more expensive) 4" filter, so I thought this might be a nice way to have numerical evidence of whether or not the filter needs to be changed. Sounds good, but is complicated by the new furnace having a variable speed blower. There's effectively 3 different speeds used depending on whether it's in high heat, low heat, cooling, or just fan on, so I marked out all three with masking tape on the gauge. In the several weeks since the furnace went in I have seen a very small increase in the static pressure indicated on the gauge, as one might expect. It will be interesting to see how it varies over the next several months. But then again, I'm a guy who likes data. You almost certainly don't need one of these, but it is kind of cool to be able to walk by the furnace and glance at this gauge to know whether it's in high or low heat and (hopefully/eventually) that the filter needs changing.

As someone else mentioned here, the quality of this manometer is on par with a piece of lab equipment.I’m using this with a waste oil burner/heater. The manufacturer of this Eliminator 120 calls for 0.03” to 0.05” before the barometric damper in the stove pipe. Another manufacturer, Energy Logic, calls for 0.04” of draft in their unit, so 0.03” to 0.05” is a good call for an oil unit, but always refer to the manufacturer specs.You only need to use the low side port. This allows the values to be on the right side of the gauge, which is more usable. If you were in an application where you see more positive pressure, you would use the high port. That was a confusing aspect to me when viewing this online. Depending on if you are seeing more negative, or positive pressure values, you can flip to either side of the zero by simply using one port or the other.I get the impression this has been made for a long time. I will never hesitate to buy one again in the future. Has allowed me to see exactly where I need to see the barometric damper for different outside weather conditions and pressures.

Last week I noticed that our radon fan had stopped running. Who knows, maybe it was 6 months ago that it stopped. It's not something we regularly check on. Anyhow, since I had to replace the fan, I did a full check of our system, which is 25+ years old. I found this Dwyer manometer in the rafters, and the fluid was empty. Since the fluid alone is $25, and the probability was that there was a leak somewhere, I figured it was best to just replace it.I installed the fan earlier today, and when the manometer showed up, it only took about 10 minutes to fill, and calibrate per the instructions. A few minutes later, after screwing in to the existing holes, everything was working.

I am using this Manometer to allow for a visual identification of when my whole house furnace filter needs to be changed. As the filters are between $30 and $40 I do not want to change too often as I will be wasting money and if I wait too long potentially damaging my HVAC system which is less than ideal..... My current scheme is to pull the filter out and look at the color of the filter which is inaccurate to say the least, so after a recent cold snap and my furnace not operating due to a filter that needed to be changed I opted to do something about it. Competitive products seemed a little cheap to me so I went this route. As a mechanical engineer by training I was very pleased with the lab instrument quality of this Manometer, when you open yours up you will be surprised by the size of the this unit, fully 6"x6" or more. Everything that I needed to accurately measure a pressure differential was included as well as a surprise built in level for that really assisted with the installation of the product.What is extremely important about this Manometer is that the first inch of the water column is essentially more "horizontal" allowing for more accuracy in the first inch of the water column. The reason for this is that your furnace is most likely designed for about 0.5" of static external pressure. This is typically found on the HVAC systems label.So in my case when I installed the Manometer and zeroed it out with no filter in place, then added a new clean filter it measured .1" rise in the water column. That is about 20% of the total rise allowed by my HVAC units spec. (By the way that was a dead on match to the Filtrete specs for this filter, which is always nice) So I will need to change that filter when the water column reads .5" of water. Having that first inch essentially expanded out is really nice so I can see what is going on visually.Long story short, if this keeps my wife happy because her house is warm as her furnace filter was changed when it should have been then all things considered this was a great purchase. :-)Have a great day and some fun as a home geek. Jeff