Asking for advice for combi boiler replacement and hydronic system upgrades

Seasoned_Amateur

New user with a new post! I installed my hydronic system a little over 15 years ago. I purchased everything from a radiant heat supply store near me and used their design. I did research things at the time, but now I know more and would do things differently, as is always the case.

For the last couple months while working from my home office, I've heard someone slamming their car door outside, only to see no one out there. Then, last week, when I was standing outside, I heard the sound coming from my boiler vent. I thought, I should get a tech over hear to analyze and adjust my combustion. Then, I realized that my Laars HT330 is over 15 years old and probably reaching the end of its lifespan. I've also started to notice that it's DHW flow detection is getting less sensitive. And, it's DHW output (3.6 gpm@80deg heat rise) has always been less than we've needed for our 2 showers. I decided that our money would be better spent on replacing, but feel free to tell me that I'm a fool.

I've been looking at different Combis to replace this unit. You'll see from the photo of my current set up that space is tight, though all minimum dimensions are respected. I like the Rinnai I-Series for it's good DHW output, quality build, concentric vent port, and similar location of inputs as my current set up. One of the things I noticed when reading the specs and instructions is that it has 1" CH connections and that their optional primary-secondary heating kit connects to a 1-1/4" manifold. After doing some reading, I realize I would probably need to upgrade my primary loop to 1" from the existing 3/4". (My Laars has 3/4" connections for CH and may have benefitted from a 1" primary, but it has worked great for 15 years.) My current primary loop does not have a manifold, but is just a loop. I'm assuming I would just purchase this Rinnai kit or make my own to fit my space better. I made a schematic of my CH system as an attached PDF. All pipes are 3/4" except for the 1/2" loops to staple up zones and radiators.

I'd love to have the 5.1 gpm of DHW that the Rinnai i120C offers, but that will mean a very oversized combi (120k BTU) for my heat load which I've calculated at about 50k BTUs. The i060C and i090C are a better match for heating, but only have 4.1 gpm of DHW. I also realize that maybe Rinnai has come out with new models in the I-Series (I-Plus) that are similar spec, but with updated features that I should be considering. My current Laars is 126k BTU and can't do CH and DHW at the same time, like this Rinnai can. So, maybe I've been using a 126k BTU boiler for heat this whole time?

So, my questions are:

Should I pipe a new 1" primary loop given my configuration? (You're gonna say "Definitely!)

Do you have a recommendation on which size boiler to purchase or should I be looking elsewhere?

Thank you in advance!

Laars Hydronic system.pdf

hot_rod

You alway size to the larger load, in your case it is the DHW production you want. The boiler you are looking at derates to 15,000 in heating mode, so it is not oversized at all. Most mod cons can be locked at that heating output.

Actually you pick up some efficiency by firing a large mod con at low firing rate. You have a large hx surface area exposed to a small burner flame and more condensation.

Most tankless water heaters and combi are rated at a 77° temperature rise so make sure you are comparing apples to apples.

Confusing is that i120C is actually a 199,000 in dhw mode?

Seems like is should be a i199C :)

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Seasoned_Amateur

Very helpful @hot_rod ! These model numbers get really hard to keep track of. I think I would be able to keep it more straight if they named them after dog breeds, instead of numbers and letters.

Seasoned_Amateur

I've got my new Rinnai IP120199C Combi Boiler and parts to build a 1" primary loop. But, I'm wondering if I need to use closely spaced tees to connect my new boiler to this loop. It has an integrated pump. My main loop will be about 5 linear feet long. My current set up does not have closely spaced tees connecting the boiler to the primary loop. I bought parts and was planning to do the tees, but then asked myself why I'm doing that. Please don't feel required to give an explanation, but I would really appreciate someone confirming that the tees are either required or a very good idea given my layout. Below are the two options for my layout, with and without tees. Thanks!

hot_rod

if you don’t have closely spaced tees in the piping somewhere, you don’t have primary secondary piping. By definition primary secondary requires hydraulic separation.

A hydro separator is another option that gives you 4 functions in one container.

Closely spaced tees

Air separation

Dirt separation

Magnetic separation.

They save you parts and labor

IMG_0872.jpeg

I imagine the installation manual shows both options, and probably not direct or series piping?

Jamie Hall

But you don't need closely spaced Ts in the primary — boiler — loop at the boiler, just where the secondary loops attach. The first of your two sketches is correct.

hot_rod

And you don't really need a loop. Here are two example. This puts the loads parallel, so no temperature drop from tee set to tee set.

Two temperatyures of a separator in the sketch

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LRCCBJ

https://forum.heatinghelp.com/discussion/comment/1825889#Comment_1825889

In his specific case, and only in this case, he has the hydraulic separation and the temperature drop caused by the return from the radiators might provide close to the desired temperature for the floor. Only in the case of reset where the returns from the rads are getting down to 140F or so would the system be a problem for him.

I believe you mentioned that the mixing valves are not too pleased with a tiny differential.

Additionally, he has not defined which mixing valve to utilize. The typical ASSE 1017 valve needs a Delta of 27F. That will be hard to achieve in the shoulder seasons.

hot_rod

without some temperature requirements it is tough to see what the temperature works out to.

assume the radiators are designed for 160, 20 delta, the second set sees 140. If the staple up needs 120 the mixer with a 17 differential requirement works. The AngleMix for example.

Some brands of thermostatic are advertising a 10 degree differential?

If radiators are not running, the mixer sees 160 SWT

If the low temperature is a single zone, you could put a manual mix valve on it. Run the boiler on ODR. Piped parallel they both always get whatever the ODR provides. Adjust the mix valve at design temperature, call it 160. As ODR ramps the 160 down, the manual mixed temperature also ramps down. They track together.

If you have some actual design temperatures, you can plug them into the what if simulation

If they are panel rads designed for 140 and the radiant wants 120. The series secondaries will not work so well with a 3 way thermostatic. Piped in parallel the mixer would get 140 always

Best option is to get the two temperatures requirements within 10 degrees of one another and just run one, as low as possible, temperature. Beef up the radiator surface area, perhaps

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Seasoned_Amateur

Thanks for the feedback. I just checked the temps on my current system that is still running. It's 37 deg outside temp, typical for Seattle morning this time of year. The house temperature inside was about 68, nearing the 70 deg thermostat. Radiator manifold in temp was 122, out temp was 112. Floor manifold in temp was 112 and out was 108. There's an outdoor sensor. It's been running with this setup for about 15 years without complaints about the heat. The radiant floor comes on about 4:30am and hits it's target of 70 deg between 7 and 8 am, then typically turns off for the rest of the day. If it's really cold out, it will come on one more time. The first floor radiators are cycling throughout the day.

hilltown

see page 57/58 in the manual, they REQUIRE primary secondary. I wouldn’t stray from the manual.

Seasoned_Amateur

Thanks, @hilltown . But, I guess I was thinking that I had primary/secondary loops without the tees. Do you have to have hydraulic separated connection to the primary loop for it to be considered primary? To my uneducated mind, it would seem like I had 3 loops (well, 4 counting my radiators and floor loops separately.) if I connected with closely spaced tees.

GGross

https://forum.heatinghelp.com/discussion/comment/1826259#Comment_1826259

Your drawing (which I put below) does indeed have primary secondary piping and is a proven piping strategy, though I would consider locating the expansion tank on the suction side of the primary loop pump

Seasoned_Amateur

Thanks, @GGross . I think I could swap the expansion tank location easily. Why is that preferred, just out of interest?

Seasoned_Amateur

I think I'm starting to understand the issue with the Delta T on my mixing valve. Given the temps I described above, it sounds like my mixing valve isn't doing any mixing most of the time. When my floors start to heat at 4:30am there would a delta T>27 deg, though I haven't checked what the return temp is at that time of the morning. Now, I won't know until the new boiler is installed since the old one crapped out last night. Thankfully, I have all of my parts in hand and can start the installation today. Thanks everyone!

GGross

https://forum.heatinghelp.com/discussion/comment/1826267#Comment_1826267

Many papers written on the topic, and the founder of this site wrote a book about it. in essence when you "pump away" from the expansion tank the system static pressure increases a little when the circulator operates, when you are "pumping toward" the expansion tank the static pressure drops a little which can cause several unwanted problems. Establishing the expansion tank as a point of no pressure change is also advantageous as this is where a fill valve will be commonly tied into the boiler system. I'm sure there are people able to better explain this than me, and there are systems that function just fine with poor piping strategies, but its always a good idea to follow best practices from the start in my opinion

https://www.amazon.com/Pumping-really-options-hydronic-systems/dp/0974396087

hilltown

I can’t explain the science of the piping however I would stress not to stray from the Rinnai manual, if you are having issues and you are having flow issues they are going to have you repipe the boiler per the manual. The internal pump is sized for what is shown in the manual.
In all cases I will always follow what the manufacturer wants. Warranty can depend on it.

You can call Rinnai and speak to the engineering department on your piping, I would bet that they will say if it’s not in the manual than it’s not approved. Typical of most all manufacturers.

Seasoned_Amateur

Thanks @GGross for the explanation. That does make sense.

Seasoned_Amateur

@hilltown Thanks for the idea to contact Rinnai engineering. They have a great chat support for tech. I shared my new layout (after adjusting for @GGross recs) and they approved my layout with the primary loop piped in 1". Now, I won't be second guessing myself as I fit this together today.

Seasoned_Amateur

I tried opening the valve to fill my boiler loop and water came shooting out of the center nipple on my Watts LF007M3-QT 3/4. Did I miss a step? I'm new to this backflow preventer. Thanks for the help.

Seasoned_Amateur

I realize now that the valve on the center test nipple was open. But, after shutting it, the center nipple drips consistently. Sigh.

Seasoned_Amateur

And, now I have an issue with the actual boiler. I went through the commissioning steps. Turned on the DHW on the boiler. Turned on a hot faucet. The boiler fired up and in a couple seconds the pressure in the boiler loop shot up past 30 psi and set off the PRV. I have all the valves open. I guess I didn't realize that the boiler loop would activate in DHW use. Is that correct?

Seasoned_Amateur

After watching a video of someone running the deaeration process with their Rinnai, I see that their pump was coming on. Mine is not coming on. There's a clicking sound of perhaps a solenoid, but the pump is not spinning.

hilltown

The internal pump should indeed come on when a DHW call is made, it will move water thru the boiler, the boiler side of the plate exchanger and the boiler loop

Take the silver cap off the end of the internal pump, maybe a touch of air, also you can see if the circ shaft is spinning

Looking at your piping diagrams, the supply and returns are opposite, on the Rinnai boiler the supply or outlet side is on the left and the return water is on the right

Seasoned_Amateur

The pump shaft is not spinning. I just ran it through deaeration again. It is definitely not spinning.

hilltown

take a 4 mm Allen and try to spin it manually

Seasoned_Amateur

I didn't see a hex head on the shaft. It looked like a flat head. Is that right?

hilltown

when in deaeration the pump doesn’t spin the entire time, it is on for a few seconds and off for a few, you should see on the controller a difference in pressure when the pump is on or off.

Seasoned_Amateur

Isthis the pump shaft?

Seasoned_Amateur

It never came in in the fifteen minutes of deaeration. I stood here with the whole time.

hilltown

take the silver cap, off, flat blade, A small bit of water, will come out just have a rag, take the silver cap 100% off

Seasoned_Amateur

How do I spin the pump shaft?

hilltown

when the cap is off completely you will see it

Seasoned_Amateur

The shaft spins smoothly

hilltown

and put the cap back on, put it in deaeration again, feel the pump can you feel it moving, does the pressure change on the control?

hilltown

or just run the DHW and see what happens

Seasoned_Amateur

Wheni run the DHW, the PRV blows in a matter of seconds.

Seasoned_Amateur

I can't feel the pump spinning. My zone pumps are very obvious. This would have to be really stealthy to be running this quiet.

hilltown

sounds like you have a piping issue.,attach a picture

Does the boiler show a 140 code

Seasoned_Amateur

No codes

hilltown

the 140 code is an overheat code