Utility system makeover

jbeamer

Before I start, I want to say thanks for this amazing community. I have bought and watched Dan's boiler video, and have learned a ton reading from many posts here. Thank you for your advice and wisdom.

I am a homeowner doing my own work on a house we have lived in for a year. I trained as an engineer, but my career took me another direction, and so I fill my desire to get back to making things work by taking on home projects. My Christmas present to myself this year is to re-do the boiler room that serves the 1930's portion of our house. The Teledyne Laars boiler in there, which has mfg date of 1983, still works but the indirect "tankless" hot water heater is leaking, the mixing valve has failed, and the whole thing is looking like spaghetti to me. The boiler cycles all the time with calls for hot water and no tank.

Here are a couple pics.

The tankless indirect water heater:


The entire system and room:


I have been impressed that this little indirect water heater keeps up with hot water demands of the kitchen, master bath and laundry. The master shower flows at 2 gpm and the current system keeps up with that. The master bath was remodeled at one point and a tub was added that I am sure has never been filled with hot water. I am reticent to size a system to a bathtub that we never use.

The boiler also serves 4 zones of baseboard radiators (living, basement, kitchen, master). The heating load here in Northern California is minimal, the 100 MBTUs for the indirect is fine for the 2500 sqft of living space that these zones span. Kids rooms and family room have separate boiler that was installed within the last decade.

My plan is to rip this all out and make it look as close as I can to the gorgeous pictures of the systems you professionals create. I'm about to pull the trigger on a Lochinvar Knight WHN155 and Squire SIT030. One of the main parameters for picking the indirect is the headroom that I have -- the Squire sits under 40 inches. It's only 27 gallons but is able to provide continuous 160 GPH; so our 2 GPM shower will be fine. With higher set point and a good mixing valve we'll be closer to filling the tub too.

The Burnham Alpine ALP150W/Alliance AL35SL combination was close for me -- the weight and dimensions of the tank worked less well. The Buderus GB142/45 and S32 tank would work too, but adds 18% more cost.

And here is the plan that I am using to order parts against:


I'll keep refining as the parts come in over the next ten days, and will post pictures of my progress and questions in this thread. I have the main system circulator on the supply side, but the boiler and hot water circs are on return -- that's from Lochinvar's documentation -- my first question is should I be changing that around? Also, does anyone know why 2 full feet of clearance below this boiler is called for? With my height limitation in the crawl space and clearance for venting I'll be skimpy there.

-jb

EBEBRATT-Ed

I would recommend you do a heat loss calculation to size the boiler. everything works better when not oversized. Personally, I add nothing for the DHW load you can do DHW priority.

The piping looks fine to me. I assume you are using zone valves for the zones and 1 system pump. The system pump should be off when no zones are calling. If done this way you should check with Lochinvar to see if you need a buffer tank. I would be concerned about minimum loop volume which can drive a boiler crazy.

jbeamer

The heat loss calculation is 80 MBTU at a temperature differential of 50 degrees (which would be a rare event). Heating is essentially optional here in Oakland -- I am fairly certain that if we were still in either Boston or Cleveland I wouldn't have the flexibility to noodle around with this myself.

So, yes, I want to size the boiler for the indirect and give the DHW priority.

Perhaps I could drop down one size to the Lochinvar WHN110 with input of 110, heating capacity of 102 and Net IBR of 89. The indirect specs says it's min coil load is 99 MBH. Are those specs compatible? I admit that I don't know which output number to pick...

Thanks for advice on the buffer tank. There's only 1.1 gallons in the heating coil of the indirect water heater. I am digging deeper into the docs now.

bob_46

Are you sure the Everhot is leaking and not just one of the connections. Everhots are solid copper , if it's shot pull the jacket off and take it to a scrap dealer $$$.

jbeamer

The leaks generally seem repairable -- the domestic hot water line into the mixing valve, the mixing valve itself, the pipe that is supporting the Everhot, the expansion tank, and the autofill valve all need replacing. I am losing pressure in the system somewhere. It was enough for me to decide to start fresh.

And yes, I'll have a nice pile of used copper for the scrap dealer.

The Lochinvar docs make no mention of needing a buffer tank even with the tiny DHW loop all summer long.

Brewbeer

Tell us about your house construction (windows, insulation, etc) and the heat loss calc. 80,000 BTUs per hour for a 50 degree differential doesn't seem consistent with 2,500 sq. ft.

Also tell us about the boiler in the other part of the house. We wouldn't be surprised if the other boiler is large enough to heat your entire house.

Zman

Brewbeer said:

Tell us about your house construction (windows, insulation, etc) and the heat loss calc. 80,000 BTUs per hour for a 50 degree differential doesn't seem consistent with 2,500 sq. ft.

Also tell us about the boiler in the other part of the house. We wouldn't be surprised if the other boiler is large enough to heat your entire house.

Your heat loss is almost certainly incorrect. I would double check it.

You can also measure your emitters to see how much heat they could possibly emit. This would give you an absolute maximum boiler size.

As for the DHW, don't get too obsessed with the manufactures charts. Assuming the heat exchanger is large enough to absorb the energy, you can figure the math for any boiler size using this:
Boiler BTU output (rated input * efficiency) / 500 (constant) / water temp delta T (diff between water entering house and desired hot water temp) = GPM.

You do not need to size DHW for the max intermittent load because the tank has storage to buffer short periods of high flow.
The bigger the tank, the less boiler capacity you need.

SWEI

Buy a KHN085 and you don't have to worry about the heat loss calc being high. It's minimum firing rate is about as low as you can get in a gas-fired boiler, so it makes a good fit for heat losses of 25k to 80k BTU/hr.