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Combi Boiler

Can anyone provide feedback on the HTP Combi Boiler, either the EFTC-144W or the EFTC-199W. I'm mainly interested in a users experience with DHW performance. For example, can it manage occasional low flow rates well, does it have any cold water sandwich issues?

According to its manual, it can recirculate internally to maintain the temperate of a small internal indirect tank (1.5gal) which sounds like it would address any low flow rate and cold water sandwich issues, but it would be great to hear from someone who has used it. Interestingly the manual also says it needs 0.5gpm to activate which is reasonable, but sounds contradictory if it's going to maintain the internal tank temperature.

Comments

  • gschallertgschallert Member Posts: 148
    The internal recirc (storage mode) is independent of the min draw rate (so not contradictory) and the small buffer tank should take care of the "cold water sandwich" issues of a typical tankless.
  • mantaraymantaray Member Posts: 7
    Thanks for the info.. If the unit is in storage mode, I assume it maintains the small storage tank set point when there is no DHW demand (0 gpm). Do you know if it will try to maintain that set point if there is a small demand, say less then the min flow rate?
  • gschallertgschallert Member Posts: 148
    The storage tank has a set point and differential which should be user configurable. The manual I pulled up said the storage tank default set point was 158 and the differential 27. The unit will fire when the differential setting is met as the tank temp drops. It will always maintain that set point independent of demand. If for some reason you don't have the .5 gpm flow on a DHW call to fire the unit the tank temp will still drop as your supply water enters. What real world use case are you worried about here where you wouldn't have .5 gpm flow?

    Btw, of the two I'd recommend the EFTC-199W as it has a better turndown ratio and higher DHW gpm output capacity.
  • Big EdBig Ed Member Posts: 878
    Hot water it's the largest load in home ... ... Figure 100,000 net BTU's = 2GPM of hot water 120K input combi ... Let's take the extreme , The Rain Forest with Body sprays some rated at 15GPM ..You would need 750K Net...Combi get it grace of 80% in full Fire hot water demand ... Just under 1Mill input ..

    As for Heat , an Combi , its low temp heating , High mass radiant or radiators... Sexy Yes,,,but if your system is designed for High temperature , Baseboard ,Hydro Air... I would recommend moving on to an good boiler and storage tank...10 min in the Rain Forest you would need 150 gallon storage tank ,Yipes

    I have enough experience to know , that I dont know it all
  • bob eckbob eck Member Posts: 586
    Looks like the 140 delivers 3.2 GPM at 77 deg temp rise
    The 199 delivers 4.8 gpm at a 77 deg temp rise
    That is all hot water. 40 degree incoming water out going temp would be 117 deg F that will need to be mixed down to take a shower. You can run two showers (at 2.5 gpm shower heads) on with the 199 boiler and with the 140 two showers one with a 2.5 gpm shower head and 1.5 gpm shower head. There are many good 1.5 gpm shower heads. You could also put a 50 gallon electric water heater in and run the domestic hot water into the water heater and the elements will keep the water in the tank hot. 50 gallons of hot water to start with and electric elements would only come on if needed. If you need more hot water use a condensing boiler with a 40, 50, 80, 100 or 120 gallon indirect water heater. Store the water at 160 deg F with a mixing valve back down to 120 deg F
    If you heating system is copper baseboard or a hydro duct coil system that uses high water temps to heat the house using a condensing gas boiler that will not run at low water temps then look at installing a buffer tank to help add water volume so the boiler can run longer cycles and has a chance to condense. You can get buffer tanks with a coil in it so you can run your domestic water through the coil to pre heat it to help out the combi boiler with cold winter water temps.
  • mantaraymantaray Member Posts: 7
    gschallert, thanks for the info.. I had a look at the manual too and came to same conclusion as you did.. My interpretation is that in storage mode, there really isn't a min flow rate. As far as real world situations, some family members like to wash dishes with some pretty low flow rates.. I somewhat measured them at about 0.4 - 0.5 gpm for the hot water. Since it was really close to the min flow rate specified in the manual, I mainly wanted to know how it would work.

    bob eck, I have a pretty big tub (needs 55gal of 110F), and we often need to run 2 showers at the same time, so I am looking at the 199kbtu model. Its min rate of 19.9 kbtu is really large for my heating needs. My design day heat loss is only about 25kbtu/h and the house has a fee zones too. I think a buffer tank (aprox 20gal) is a must with this plan. Alternatively I would prefer to go with a much smaller boiler (say 8k to 80k) and an indirect (aprox 50-55gal) but I sadly don't think I have space for that approach. I need a solution where the boiler could sit directly above the tank, without much wall height. A small buffer tank will fit under a combi, but I don't think I will find an indirect short enough to make that work.
  • gschallertgschallert Member Posts: 148
    edited November 14
    mantaray said:

    gschallert, thanks for the info.. I had a look at the manual too and came to same conclusion as you did.. My interpretation is that in storage mode, there really isn't a min flow rate. As far as real world situations, some family members like to wash dishes with some pretty low flow rates.. I somewhat measured them at about 0.4 - 0.5 gpm for the hot water. Since it was really close to the min flow rate specified in the manual, I mainly wanted to know how it would work.

    Not sure I understand about the washing dishes....by hand turning tap on and off or using a dishwasher? Dishwashers nowadays heat their own water up to temp and I'd honestly pipe that off cold water line or install a small 2 gallon point of use electric for it if I had really cold inlet temps.

    Probably out of your budget but the Viessmann 222-F (35)would likely meet all your needs (footprint/tub fill/concurrent showers) providing you switched to low flow shower heads, which IME most don't even notice.
    https://www.viessmann-us.com/en/residential/gas-boilers/condensing-boilers/vitodens-222-f.html
  • bob eckbob eck Member Posts: 586
    Use the Lochinvar Noble 199 boiler it delivers 4.8 GPM at a 77 degree temp rise.
    Under the Noble boiler hung on the wall install a Vaughn Hydronic Buffer Tank 20 gallon that is 32 3/4" high. This will give you your P/S piping. Get Vaughn to install a 3/4" coil in this tank.
    Take your cold domestic water run it through the coil in the buffer tank and raise cold winter water temp from 40 degrees to 50 degrees or higher. Doing this the combi boiler should be able to deliver more than 4.8 GPM hot water.
    Call Lochinvar at 800-722-2101 see what their engineers say if this will work.
    Where are you located at? Get your heating contractor to contact me I can price them the boiler and the Vaughn buffer tank with coil.
    email is [email protected]
  • mantaraymantaray Member Posts: 7
    mantaray said:


    Probably out of your budget but the Viessmann 222-F (35)would likely meet all your needs (footprint/tub fill/concurrent showers) providing you switched to low flow shower heads, which IME most don't even notice.
    https://www.viessmann-us.com/en/residential/gas-boilers/condensing-boilers/vitodens-222-f.html

    That is a very nice system, sounds like it would meet all my needs. I image you get what you pay for, but it will very likely be out of my budget.
  • mantaraymantaray Member Posts: 7
    bob eck said:

    Use the Lochinvar Noble 199 boiler it delivers 4.8 GPM at a 77 degree temp rise.
    Under the Noble boiler hung on the wall install a Vaughn Hydronic Buffer Tank 20 gallon that is 32 3/4" high. This will give you your P/S piping. Get Vaughn to install a 3/4" coil in this tank.
    Take your cold domestic water run it through the coil in the buffer tank and raise cold winter water temp from 40 degrees to 50 degrees or higher. Doing this the combi boiler should be able to deliver more than 4.8 GPM hot water.
    Call Lochinvar at 800-722-2101 see what their engineers say if this will work.
    Where are you located at? Get your heating contractor to contact me I can price them the boiler and the Vaughn buffer tank with coil.
    email is [email protected]

    I like the idea of using a small indirect tank with the main volume used to buffer the heat side and the coil to pre-heat the domestic water. Good idea, and it will fit in the space I have.
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