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Rinnai Boiler Excessive Fuel Consumption Problem

BS_Alaska Member Posts: 3
I am building a new house and installed Rinnai Q85SP on demand boiler for in-floor radiant heating and RC80i on demand water heater for domestic use. We started using them in October with a full tank. Our house size is 2000 sqft, plus garage and work shop1000 sqft. 40 days later the first bill came, it showed over 300 gallon use. It was only for the house heating. The house was under construction status but had been spray foamed (2 to 3 inches -R13) before we started heating with the unit. I know R-13 is light insulation but under construction using 5 small ceramic heaters we were only paying just over $400 to heat the place to 60 degrees.

During Christmas the temp dropped to single digits (5-9 above) and the unit stopped working and the house temp dropped, the service tech has no idea why it stopped working. Is this common?

At the end of December they filled the tank again and it needed another 300+ gallons to fill it again and just before Christmas we had R-55 in the attic. Twelve days latter the fuel usage was 2.3 gal per day, another twelve days later it used just under 5 gal per day and the outside temp was in the 30's for that period.

The dealer has no idea what is going on and we have great concerns overt this.

Any ideas what the problem might be? Could it be the size of the unit or a bad unit?

Your insight would be greatly appreciated.



  • Jack
    Jack Member Posts: 1,046
    Get your dealer onto the Rinnai tech line

    800 621-9419 Trying to analyze fuel usage while under construction is kinda hard. Your fuel consumption figures of 2.3 gpd or 5gpd does not seem excessive. At 5 gpd you are looking at about 19000btu/hr of heat loss. That is not excessive.

    There are 4 programming chapters in the unit. Parameters for set-up, Info for 18 specific details from water temp in /out, outdoor temp, % of power, total seasonal consumption and a bunch more. If you look into the INFO section of the display the boiler will tell you exactly what it is consuming and also give total energy consumption in kWh (1 kw = 3,414 btu). You also have a Service and Error section. Have your dealer show you the Info section, but DO NOT fool with Parameters. That is his job.

    Has your dealer done a proper set-up on the unit? Did he use an oxygen analyzer? What type distribution system do you have? Baseboard? Radiant? Combination? What re-set curve is the unit operating on?

    I'm sorry to play 50 questions to your questions but you are getting the idea. I could throw a dart at the question but need more info. That is an excellent unit and will heat your house well and efficiently.
  • BS_Alaska
    BS_Alaska Member Posts: 3
    Great advice and starting points

    You have allot of good ideas that I need to follow up on and I will.  The dealer says he is talking with them but I think he is learning as he goes along. I will have him go through the unit we me present so I can try and understand the unit better. The dealer can't figure it out and it is driving him crazy, he has suggested putting in the next larger unit and see if that makes a difference and we are thinking about letting him do so.

    The house and garage is in floor radiant heat. we keep the garage and shop area at 55 and the house at 64. The house has a HRV system and we started using about the same time as our last fill. I am thinking that is the cause of the increase because it was running all the time. Thank you for your time and when I get the answers to your questions I will get back to you.
  • Jack
    Jack Member Posts: 1,046
    If it is all radiant

    You should be on reset curve 4. Again that is in the parameters menu. Switching boilers is the last thing you want to do. Let me repeat, the last thing you want to do. The programming is simple...Once you have done it a few times. You have the manual. Follow it carefully. Before getting into the programming mode, examine the options and write down what you need for that specific parameter. Then go at it. As you step thru the parameters write down the default settings on your boiler.

    In looking at it, I think you need to adjust parameter #2 to 4 and calculate the vent length altitude compensation factor for #73. The worksheet for 73 is clearly laid out in the manual

    What is the heat loss for your home? Any information you provide should be prefaced with that info.
  • SWEI
    SWEI Member Posts: 7,356
    running all the time

    is a good thing with a modulating boiler.  Do not upsize without a proper heat loss calc.
  • BS_Alaska
    BS_Alaska Member Posts: 3
    Your the man, thanks

    Jack, I will be meeting with the installer

    /dealer this week or next and we will figure out what changes we need to make using the information you provided. Once I have the answers to your questions I will send you an email once again. Thank you for your time and helping us try and save energy  which is the main reason we went with this system.

  • heatpro02920
    heatpro02920 Member Posts: 991
    hope this helps

    I would start with an audit, have someone come out and go around the building with a thermal imaging camera and make sure you are not losing the energy anywhere {more than expected} Some hvac contractors keep thermal imaging equipment with them {I have it on a couple of my trucks}, if all looks well {also check the radiant, was this properly installed with insulation, I have seen system just soaking the ground with heat because no one insulated around the footing}... Then I would do some common sense math, I have had customers complain about fuel usage and I go in their home to find the t-stat at 80* and 2 bathroom fans just constantly running pumping the heat outside....

    Next check for leaks, a simple pressure test will make sure you are not just leaking lp into the atmosphere...

    As far as the Rinnai boiler and water heater, I wouldnt resize anything until you are sure it is undersized... This could make your problem worse.....

    BTW, I don't think you are getting terrible fuel consumption, but I do think you should be getting better for what I have read...
This discussion has been closed.