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L7224U - Outdoor Reset with Oversized Boiler & Baseboard?

NTL1991 Member Posts: 103
edited February 2018 in Thermostats and Controls
I've got everything I need to install a Taco ZVC405-4 to clean up my zone valve wiring and give me priority for my Boilermate (pipe with zone valve).

I have a newer L7224U digital aquastat and I'd like to install the outdoor reset kit soon, so I'm thinking about using the "duu" option - ZR DHW Request. This will force the boiler to high limit for a DHW call, and will drop back down to the outdoor curve for space heating calls on the other 4 zones.

How should I be wiring this? My boilermate's aquastat will be wired to Zone 5 Priority on the ZVC, but the L7224U is looking for line voltage on the ZR contact.

Should I be using the ZVC's Zone 5 Pump End Switch contacts, with Common connected to L1 and N/O connected to the L7224U's ZR terminal? When the DHW calls, the zone valve will open, closing the end switch, which will close the Pump End Switch, which will supply 120V to ZR on the L7224U, which will power the circulator and fire the boiler to High Limit. Is this correct?
Nick, Cranston, RI


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,459
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  • NTL1991
    NTL1991 Member Posts: 103
    Thank you, Robert.

    I have the ZVC405 all wired up and I love it. There are lots of wires for 5 zones, but they're neat now, routed all the same way.

    I ordered my Honeywell wired outdoor reset module, and I'll be installing that next week along with a new R7284U Primary Control for the burner.

    I noticed that if the indirect (priority) calls for heat while the burner is on for a space heating call, the ZVC will turn off the space heating call, which cuts out the burner, enable the indirect zone and when the indirect's end switch closes, starts the burner again. Hearing the burner short cycle like that is a little annoying.

    Maybe the electronic R7284 will give me some sort of delay so it's not as noticeable.
    Nick, Cranston, RI
  • SuperTech
    SuperTech Member Posts: 1,803
    I have the L7224U with the outdoor reset module. I just don't have the indirect tank (yet). I believe the L7224U has an anti short cycle setting that may help you out. I've been extremely happy with this aquastat and reset module.

    Just curious, what kind of boiler and heat emmiters are you running? What are you going to set the design temperature as? Do you have any concerns about the possibility of developing flue gas condensation?
  • SuperTech
    SuperTech Member Posts: 1,803
    And I also have the R7284 primary control. I keep it set for a 15 second pre purge and 30 second post purge..

    I still can't figure what all the EnviraCom stuff is used for. I would like to be able to use the outdoor reset module to display outdoor temperature on a thermostat. Perhaps a Honeywell vision pro 8000 can accomplish this.
  • NTL1991
    NTL1991 Member Posts: 103
    edited February 2018
    I think you're right about the short cycle protection. I remember reading about it in the manual, I'll have to take a look, it might be just what I need.

    The boiler is a ~10 year old oil-fired cast iron Utica, which is pretty oversized. House is circa 1870s, completely gutted to four exterior walls and rebuilt, insulated, wired to 1968 standards after a total loss fire. House is approximately 2,100 sq ft. All windows have been replaced with modern vinyl double glazed units.

    -First floor zone, 900 sq ft, with a heat loss of about 20K BTU/hr. There's about 43K of baseboard installed.
    -Second floor zone, 900 sq ft, with a heat loss of about 18K BTU/hr. There's about 42K of baseboard installed.
    -Patio room, 300 sq ft, with a heat loss of about 10K BTU/hr. There's about 19K of baseboard installed.
    -Basement Workshop Heater, 16K BTU/hr Unit Heater
    -Amtrol BoilerMate 41 Gal Indirect Heater

    The boiler is rated at 175K BTU. The installer sized it to the connected load, plus some. The heat loss is only about 50K BTU/hr. This is my parents house. They use very little hot water, don't ever go upstairs (4 bedrooms all unoccupied - thermostat stays off), and rarely use the workshop heater. They spend 90% of their day in the patio room.

    The boiler is currently cold-start, with a 180 degree high-limit. I think the baseboard could keep up comfortably at a lower temperature, but with the cast-iron boiler, there are limits. I think this house could really use a ModCon when the time comes to replace it...

    I'll probably try for 160 high and 140 low on the outdoor reset at first, with a high limit of 180 for the indirect. (Tbh, though, they probably could get away with the indirect operating on only 160* water seeing how little they use.)

    I do like the pre-purge feature on the R7284. It assists with establishing flow up the flue, but it also stops the abrupt "bang" when their current burner fires instantly. It kind of eases into the firing. Not sure if I'd set the post-purge as it would be sending valuable BTU's up the flue.

    Any thoughts on any of this?
    Nick, Cranston, RI