Ask Dave! – FuelMizer

Q. Hey Dave, I want to use the FuelMizer in a project and after analyzing the house and measuring the existing radiation (baseboard) installed, I can heat the house with 160 degrees rather that 180F. This way with the condensing boiler I can gain some extra efficiency points with a cooler return temp. How do I set it up? – Dan, Long Island.

P.S. The boiler only modulates the BTU output, not the supply water temp, that’s why I want to use the FuelMizer.

A. Dan, Excellent job in “doin’ the math” and finding out that the existing radiation installed is more than what the house actually needs. The instructions with the FuelMizer describes where you need to have the dial set to get 180 degree water when it reaches design temp in your area. For Long Island, the outside design is 10 degrees based upon Manual J standards for Suffolk County AFB. If we take a look at the reset curves in the instruction, our line is not there. In order to create a “new one,” we have all off the information we need already; 10 degrees ODT (outdoor design temperature) with 160 degrees SWT (supply water temperature). Find that point on the graph and with the other point being 70 ODT and 70 SWT, connect the dots with a line going through up to 180 SWT and off the chart.

FuelMizer Reset Curves

Now draw a straight line down from where we intersect with the 180 horizontal line and find the ODT, we see we are at -5 degrees. Turn the dial to -5, and you are all set. This means if it gets to -5 ODT, then the boiler will produce 180 degrees F. If it happens to get colder than 10 outside, the boiler doesn’t stop at 160, we are still working on the reset line here. This is where we can get that extra “fudge” when it may get colder than 10 outside.  Dan, there is one more thing to remember; take Dip Switch number 1 and place it in the “Off” position for use with a ModCon boiler.

I hope this helps Dan, Enjoy!

Q. Hey Dave, What is maximum amp rating on the FuelMizer pump relay and are there any issues using it in conjunction with a motor starter for larger pump applications? – Jeff, Colorado.

A. Great question Jeff, thanks for thinking a little outside the box on this one. I am sure you are thinking of using the FuelMizer outside of residential applications and you can. There is no limit on the amount of BTU’s of the boiler system. All the FuelMizer does is


modulate the boiler temperature based upon the Outside sensor and the supply sensor of the boiler. It does not know the size of the boiler at all. So to answer your question, the maximum circulator that can be directly connected and controlled by the FuelMizer is a 1/3 HP motor with 6 full load amps and that will get you a lot of pumping power. If you need to go larger, you can use a starter; just remember that the FuelMizer is going to switch 120Volts so make sure that the input on your starter relay can handle that for an input.

Thanks guys, keep ‘em coming. You can post comments here or email me your questions at


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2 Responses to Ask Dave! – FuelMizer

  1. Tom says:

    Hey Dave,
    I just installed my First FuelMizer! At to my buddies mother-inlaws house after hearing her say she pays $6,000 for oil a year for heat and hot water. I talked to her about adding an out door reset control to her system explained how they worked and it would save her at least 10-15% to her fuel cost and usage. I was unable to convince her to also add a Taco Pump control at the same time which would of made the install a little easier and cleaner. She has 3 heating pumps and 1 DHW pump. I had to reuse her 3 honey well pump controls which got me thinking there need one more dip switch setting and another relay to control the DHW pump any time there is a demand for just DHW. With the current setup the pump turns on any time the t-stat calls for heat or when there call for the DHW. I installed a RIB relay to control the DHW pump. Also wired my
    t-stat terminals though all three 3 normally open control contacts on the Honeywell pump relays. Thank you guys for a great product can’t wait to install more taco controls in the future.

  2. Pingback: Baseboard, Radiant, and Boilers, ….Oh My! |

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