Question Regarding Plumbing Course | Sect 5.8 | Tankless Coils From Boilers Illustration

I’m currenty reviewing all course materials, a second time, in preparation for the final exam.

In reviewing the Plumbing Course, section 5.8 specifically, I noticed that the ‘tankless coils from boilers’ illustration appears to be missing a couple of components, and potentially a misplaced component.

I’ve included the illustration, which I modified to show the locations of concern

Hoping a second set of eyes could confirm, and or clarify the following:

1). Incoming domestic water - Shouldn’t there be a check valve\backflow preventer with an atmospheric vent installed?
2) Incoming domestic water - Shouldn’t there be a pressure reducing valve installed after the check valve\backflow preventer?
3) Cold water return - there appears to be a pressure reducing valve here - do these systems require a reducing valve at the return?

The feed on a hydronic boiler does need an approved backflow prevention device and a pressure regulator. The boiler also needs a low water cut off in new installs. The tankless coil inside a boiler does not require a backflow prevention valve or a pressure reducer, what it does need is a thermostatic mixing valve to temper the water down to 120f. What you’re referring to as a cold water return is actually a feed to the boiler that ties into the boiler’s return and it does need a 12PSI pressure regulator because a typical residential hydronic boiler is a closed loop system that operates at 12-20PSI. The required pressure relief valve is set to 30PSI, so if the feeder feeds street pressure exceeding 30PSI, the pressure relief on the boiler would blow. This should be explained in the NACHI course. Now, as far as the tankless coil and installing a backflow prevention valve on its feed side, while in theory the coil can develop a hole in it and then allow the boiler’s water to enter potable water, the risk is too low and the requirement is not part of any code I know. Hope that helps :slight_smile:



Yes, your input was helpful. Thank you!

The video about tankless water heaters and boilers within the Plumbing Course left me with several questions. I typically find myself doing A LOT of further research VIA internet, but it was hard to find a video explaining the plumbing connections, or a good diagram with direction of flow. After a bit more digging I found more pieces (not all) to my puzzle. For example: the plumbing on the left is the primary loop (i.e. domestic water), which is circulated VIA an internal pump. The plumbing on the right is the secondary loop, and its doing the hydronic heating, and powered by an external pump (s).

The primary and secondary loops usually refers to hydronic heat piping. The tankless coil is what’s inside the boiler and is used for domestic water. It does not require a circulator. It works just like a normal water heater, water goes in cold under street pressure, picks up heat from hot water of the boiler, and exits heated. The circulator is needed on the space heating side of the boiler because it’s a closed loop system.

Thank you for that clarification!

Good stuff Simon!