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Any boiler can become a "combi"

hot_rod
hot_rod Member Posts: 16,568
Some folks are intimidated by all the extra components and OEM parts involved in combis. Extra pump or diverting valve, mono-bloc assemblies, complexity, etc.

At days end, it's just a HX, flow switch and pump or 3 way valve.

I built this for my shop yesterday. I only have a 50,000 boiler, so mainly for washing hands, squirting the truck off DHW.

Im had this HX module in a nice PP enclosure. A Sika .5 gpm flow switch and a 15-58 Grundfos.

When a hw tap turns on the flow switch wires to the DHW "call" in the boiler. This Lochinvar has that DHW enable connection as well as a 120V pump connection. Basically 4 wires. The boiler goes to full fire 180F on DHW call.

In takes 43 seconds to feel warm water at a 1/2 gpm or so flow. Some combis allow an "always hot" HX so hot water within a few seconds.

All the components are outside the box, easy to service.

I have a Moen PosiTemp shower valve ordered as the shop hose connection.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
STEVEusaPAmattmia2Solid_Fuel_Man

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,342
    Any boiler cam become a steam boiler. For a few minutes anyway...


    I remember making a pool heater out of an old 30 gallon gas water heater tank setting on top of a portable combustion chamber we used to have for training purposes. It was sitting in the garage for over 20 years when I got the idea. It was a temporary setup. Then I forgot to turn it off and the straight PVC discharge pipe became a U shape PVC discharge pipe. After that I installed an aquastat and set it to 140°

    But I get your point Bob.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
    Solid_Fuel_Man
  • mattmia2
    mattmia2 Member Posts: 5,753
    The "keep warm" function of a combi seems much less efficient than a modern well insulated indirect.
  • hot_rod
    hot_rod Member Posts: 16,568
    mattmia2 said:

    The "keep warm" function of a combi seems much less efficient than a modern well insulated indirect.

    Yes it does cost some energy to keep the HX warm. In winter heating mode the boiler stays warm without that function, so it is mainly the months where there are ho heat calls.

    Start up is not much different from a tankless WH.

    Of course indirects have a lot of surface area that losses heat also. even with 2" of insulation they drop temperature.

    Even if indirects do loose 1° an hour, which I feel is optimistic :) by the ratings. That 24° a day, enough to fire the boiler several times a day.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,342
    edited March 21
    hot_rod said:
    The "keep warm" function of a combi seems much less efficient than a modern well insulated indirect.
    Yes it does cost some energy to keep the HX warm. In winter heating mode the boiler stays warm without that function, so it is mainly the months where there are ho heat calls. Start up is not much different from a tankless WH. Of course indirects have a lot of surface area that losses heat also. even with 2" of insulation they drop temperature. Even if indirects do loose 1° an hour, which I feel is optimistic :) by the ratings. That 24° a day, enough to fire the boiler several times a day.
    Over 20 years ago we installed a Buderus Indirect. Buderus claimed the tank lost 1/2° Per hour so I timed it once to see if it was true. Using a data recorder, it took about 18 hours to bring the burner on to reheat the tank while the home was unoccupied. So either the temperature dropped faster than 1/2° per hour or the control differential was only 9° 

    That comes out to 1.3 times per day. Or just a little over five times every four days. Either way, I was satisfied that the insulation on the tank was pretty darn good.


    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
    Solid_Fuel_Man
  • hot_rod
    hot_rod Member Posts: 16,568


    hot_rod said:

    The "keep warm" function of a combi seems much less efficient than a modern well insulated indirect.
    Yes it does cost some energy to keep the HX warm. In winter heating mode the boiler stays warm without that function, so it is mainly the months where there are ho heat calls.

    Start up is not much different from a tankless WH.

    Of course indirects have a lot of surface area that losses heat also. even with 2" of insulation they drop temperature.

    Even if indirects do loose 1° an hour, which I feel is optimistic :) by the ratings. That 24° a day, enough to fire the boiler several times a day.

    Over 20 years ago we installed a Buderus Indirect. Buderus claimed the tank lost 1/2° Per hour so I timed it once to see if it was true. Using a data recorder, it took about 18 hours to bring the burner on to reheat the tank while the home was unoccupied. So either the temperature dropped faster than 1/2° per hour or the control differential was only 9° 

    That comes out to 1.3 times per day. Or just a little over five times every four days. Either way, I was satisfied that the insulation on the tank was pretty darn good.





    Several unknowns in all the claims out there. The tank size (its a surface area calculation), the tank height to some extent with stratification factor in. Actual tank temperature, the room temperature. Heat trapper nipples?

    The wider that delta between tank and ambient the faster the heat leaves the tank. Any drafts from combustion air entering the room would change the results also. No amount of insulation can stop the heat transfer from warm to cool completely.

    The solar industry pushed for 4" insulation on tanks years ago, but the price adder made the upgrade impossible to sell to the consumer. No amount of insulation can stop the heat transfer from warm to cool completely, so it is a diminishing returns decision.

    A rep told me they took 6 different tanks into a tank manufacturers lab in RI for comparison testing, years ago. To get the number they wanted the room had to be 80F, I don't recall the tank temperature for the testing. I'd suspect 120F, about the lowest usable tank temperature, to call it a water heater tank :)

    So you can set the test parameters to get the results the "other guy" claims. Or better.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Solid_Fuel_Man
  • tim smith
    tim smith Member Posts: 2,460
    I have been after a 5 gals shell and coil heat x for a long time. Its the ideal size I feel to give a buffer for immediate draw but not store any to speak of. Would have to be a pretty packed coil to get the recovery needed although. They make real expensive sanitary ones of labs but waaaaaay out of most budgets.
    Solid_Fuel_Man
  • hot_rod
    hot_rod Member Posts: 16,568
    tim smith said:

    I have been after a 5 gals shell and coil heat x for a long time. Its the ideal size I feel to give a buffer for immediate draw but not store any to speak of. Would have to be a pretty packed coil to get the recovery needed although. They make real expensive sanitary ones of labs but waaaaaay out of most budgets.

    An Ever-hot? They look to be about that gallon capacity.

    There were some solar drainback tanks that had coils in them. HTP offered them for a while. I don't see them on their site anymore.

    I may see how much 3/8 CSST I can shove into a 6 gallon electric tank. If you heat the CSST you anneal it and it becomes easy to form. This gob of 3/8 I was able to wrap tight enough to fit into a 2" opening on a tank.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    MikeAmannSolid_Fuel_Man
  • mattmia2
    mattmia2 Member Posts: 5,753
    You could always just get the smallest indirect you can find, there isn't a whole lot of difference between a large shell and tube HX and a small indirect. Maybe the HX has more transfer surface area.
  • hot_rod
    hot_rod Member Posts: 16,568
    mattmia2 said:

    You could always just get the smallest indirect you can find, there isn't a whole lot of difference between a large shell and tube HX and a small indirect. Maybe the HX has more transfer surface area.

    Have you seen any indirects smaller that 20 gallon? I guess at some point you could buy a shell and tube HX with the capacity you wanted. Probably big $$s
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,500
    I wonder how long that CSST would hold up inside a tank? 

    There would be a market for a coil like that would go into an 1-1/4" element opening on a 5 gal electric water heater. Then the tank is just connected in series with the Combi. 

    Like a hybrid, combi/indirect. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • hot_rod
    hot_rod Member Posts: 16,568

    I wonder how long that CSST would hold up inside a tank? 

    There would be a market for a coil like that would go into an 1-1/4" element opening on a 5 gal electric water heater. Then the tank is just connected in series with the Combi. 

    Like a hybrid, combi/indirect. 

    I have seen those DHW lances in the UK that slide into a blank "cylinder to make it an indirect. They look more like a 2" hole size.
    I'll look for a 6 gallon tank to see how many feet of CSST I can push into it. I saw tanks at the Intersolar show years ago with csst coils in them. High chloride water may take out that thin stainless, however?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Solid_Fuel_Man
  • SootBoy
    SootBoy Member Posts: 14
    hot_rod said:

    tim smith said:

    I have been after a 5 gals shell and coil heat x for a long time. Its the ideal size I feel to give a buffer for immediate draw but not store any to speak of. Would have to be a pretty packed coil to get the recovery needed although. They make real expensive sanitary ones of labs but waaaaaay out of most budgets.

    An Ever-hot? They look to be about that gallon capacity.

    There were some solar drainback tanks that had coils in them. HTP offered them for a while. I don't see them on their site anymore.

    I may see how much 3/8 CSST I can shove into a 6 gallon electric tank. If you heat the CSST you anneal it and it becomes easy to form. This gob of 3/8 I was able to wrap tight enough to fit into a 2" opening on a tank.
    "Everhot" was located in Boston's South End on Appleton St. i had the pleasure of going in therein late 70's and watching these guys heating and bending the tubes.. I had not thought about that forever untill seeing this post. There used to ba lot of "Side Arm" Tankless's in Boston on old steam boilers you would have to keep the water above top of tank and align to the sight glass they had a key vent on some of them i know cause i broke one off ...
  • I took this Everhot out of a house in Berkeley. Waiting for the chance to use it.


    Often wrong, never in doubt.
  • JUGHNE
    JUGHNE Member Posts: 9,828
    I needed a heat exchanger for my house.
    At my FIL farm he had an iron pile with 3' of 6" with a flange welded on the end.
    So from that this was built.
    The bottom base plate was welded on to close up the open end.
    The top flange was fabricated at the factory the FIL retired from.

    The spuds are all steel merchant couplings.

    The copper tube bundle consists of 8 X 30" of 3/4 hard L....a full stick.
    90's and st 90' make the returns.

    Die electric unions on each side of the top plate, (I am surprised they have not leaked).

    The only real money in this is the copper/fittings/relief valve and the top plate fabrication was "donated".



    It is fired by a Loch KBN 80 on the DHW priority @ 180 degrees.

    It feeds this tank;



    That is an "air head" solar tank....bargain buy from supplier...120 gallon.
    3 top ports and upper electric element.
    Tank has been in use since 1995....pretty good water here.

    We used the electric element for a couple of years until the HXC was located.
    mattmia2Alan (California Radiant) Forbes
  • mattmia2
    mattmia2 Member Posts: 5,753
    That would be a great way to make a reverse indirect.
  • JUGHNE
    JUGHNE Member Posts: 9,828
    Do you mean to use the 4500 watt element to heat the house?

    I thought about that and figured it might work as freeze prevention only.
  • mattmia2
    mattmia2 Member Posts: 5,753
    The section of pipe with the blank flanges and the coil inside. Fill it with boiler water and make dhw with the coil.
  • JUGHNE
    JUGHNE Member Posts: 9,828
    That is what I am doing.
    This was built in the late 90's.
    In use for 20+ years.
    mattmia2