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fwmech · October 5

Hello all,

I am new to the mod con, combi world. I moved from an area that had fuel oil only so this is my first go at installing these new units.

I have a before and after picture here of a Navien that I replaced with a Lochinvar.

I'm looking for feedback on if I accomplished the goal of primary secondary. The Lochinvar has an internal system pump so the boiler loop is the primary.

I got the idea for the "moose antler" installation from either a Taco after dark or coffee with Caleffi webinar where it was suggested.

I made the primary and manifold piping 1-1/4" because the boiler is 199,000 BTU.

I have more of these installs lined up so please let me know what I can do better. Thanks!

mattmia2 · October 5

Why would the water flow out through the system instead of through that bypass?

neilc · October 5

I think your neutralizer is upside down, the outlet wants to be high to hold back a reservoir there, for more neutralization time,

Kaos · 12:50AM

Very clean install, easy to service. I find manifolds add a lot of value and save significant install time. If you need more flow than the typical ones, Watts has high flow series that will do 4GPM per port.

Besides the correct hydraulic circuit, the other important bit is the setup and configuration. Is the outdoor sensor installed? A reasonable reset curve to match emitters? Space heat limit set to a reasonable value above expected space heat load? These bits are just as important as it will effect the actual efficiency of the unit and how much it will cycle. Short cycling is the silent killer of modcons. Also a bit of education of the home owner to understand that with outdoor reset recovery will be slower so they have to change the programming on their thermostat.

One small improvement with any combi or tankless unit. A small 5 gallon plug in tank with 3/4" ports on the outlet of the unit will eliminate any wait time without having to keep the boiler running by enabling combi pre-heat.

hot_rod · 2:40AM

I have that boiler, I think the boost function over rides the ODR, so recovery should be adequate

fwmech · 5:34AM

https://forum.heatinghelp.com/discussion/comment/1866812#Comment_1866812

Thank you! I'll fix that tomorrow

fwmech · 11:53AM

https://forum.heatinghelp.com/discussion/comment/1866839#Comment_1866839

I am working on learning the right way to set the inputs. So far using Lochinvar U videos. There are three zones of baseboards and I have a 140° target system temp running right now. I am not happy with the ∆T, it's only 5-10° lower on the return temp. The Taco 0015e3 is set on medium speed, I'm thinking about going to the low speed. I don't suppose anyone uses a circuit setter residentially, right? I'm a former commercial and industrial and I'm learning what's common and available residentially as I go. Thanks for the help!

The outdoor reset is installed, on the North wall of the home.

Intplm. · 12:40PM

When installing these, one thing to do is allow as much room as possible for serviceability. All too often these things get crammed into tight spaces.

Kaos · 1:17PM

https://forum.heatinghelp.com/discussion/comment/1866863#Comment_1866863

This falls into the category of the benefits outweigh the risk of a callback. Especially with series fintubes, higher delta T will reduce output on the last emitter, nobody likes cold rooms. Higher delta T with modcons is your friend in most other cases though.

140F is a good target if you can get away with it. If the previous setup was ok at 140F, or the owner is the type that can adjust it if needed, otherwise set a bit higher to avoid callback.

Even going as far as checking delta T is more than most residential techs will do, typically pumps are installed and set to max.

hot_rod · 2:36PM

.Not to worry about that ∆. The delta is always moving a bit until you reach thermal equilibrium. The point when temperature has stabilized, not increasing or decreasing across the loop. At that point you should be at design ∆. Probably most systems never are, as @Kaos suggested. It is rare that an installer checks these numbers. It could take hours, days, for a large concrete slab to reach thermal equilibrium on cold start up.

Lower delta= higher heat transfer rates. It does cost a small bit more pumping, and you want to stay below 5 fps velocity to keep things quiet.

Here is the rational for the increased output:

You would need to get up around 8 gpm in 3/4 M copper to exceed 5 fps

Idronics 23 is a good read for understanding heat transfer in Hydronic systems

Lots or residential insyallers that want to know or check flow rates install Quicksetters as you do not need a $3000.00 B&G delta P meter to read them :)

mattmia2 · 3:32PM

You're measuring the delta t on the individual zones, not the boiler or supply and return mains, right?

fwmech · 3:47PM

Thank you very much for the feedback, fellas.

I have a Knight boiler as my next job. I'm leaning towards the floor model because there will be an indirect water heater so I'll need to build a platform anyway.

@hot_rod I will read that issue of idronics, thanks for the knowledge! I am trying to remember where I read about the 1-1/4" vs 1" primary loops and at what BTU you see better performance... Perhaps in one of Dan Holohan's books. That's very interesting information about the boundary layer, I'm interested to learn more

@Kaos That is very helpful input! In one of the Lochinvar U videos, the trainer was talking about setting the parameters in the programming to essentially get rid of the warm weather shutdown giving the homeowner control of the boiler via the thermostat. I hadn't really thought about how coaching them to adjust the ODR parameters to bump up the target temp would save me the hassle of a call back. Luckily we're not too cold outside yet so I have some time to learn the system so I can then try to teach it to them.

mattmia2 · 3:51PM

If the total radiation connected is less than the output of the boiler, it may calm things down to limit the maximum firing rate for the heat call to match it.

hot_rod · 5:03PM

I've used all; these functions on my Knight. It takes some trial and error to get it set exactly to your application. I really like this control.

Properly dialed in you can get close to continuous firing, a very efficient operating mode.

The ramp delay takes some practice, don't get too aggressive or you delay heat.

I know the boost overides the ODR, but not sure if it over rides the ramp delay?

Screenshot 2025-10-06 at 10.58.48 AM.png

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