Excited about Boiler Design

thank you! I ordered that hole saw, and it should be here tomorrow.

no plans to reuse any of the devises removed from the tank that I scrapped for $4, but I did leave them sitting out front of the garage door in case I discover some magical use for them (boiler drain Valve, pressure relief, and natural gas controls). I will probably keep them all a few years before discovering they are wasting space. Some day when all my projects are done I will need far fewer tools and spare parts laying around. Some day.

A little OT, but my basement is smelling like sewer gas since the water heater failure. Maybe the hot water down the floor drain sewer line or some dead animal in my basement caused it, but it doesn’t smell near the laundry room floor drain, more around the area that another above-ground cast sewer line goes into the ground. There are “french drains” around it that could be letting out gasses that are finding their way out of the ground. I don’t know. The outside ground is surely frozen right now. So maybe some dinosaur is decomposing under my house, or maybe I just have a sewer gas leak, or maybe something got wet that I’ve yet to discover. Anyway, now I’m looking to buy a sewer gas leak detector. Methane? Natural gas? I guess a natural gas sniffer might be good to have, I don’t know,

yes. Thank you. SDS Plus adapter in the same brand as the core saw was available for $24 and should arrive tomorrow. So, as soon as I’ve got my positions marked and the business around the holes cleaned up, I should be ready to roll. The tolerances will be tight with the 3.5”. It should work great.

working on my layout, I’ve noticed that the higher vertical space available between joists would be better for large 3” holes, and I was planning to go out the back side of the house that has side-to-side joists. While I could drill holes and support the joists, it certainly would be my preference to not cut them. I may be looking to reduce to 2” PVC as my boilers allow for that, or perhaps using a concentric vent. Maybe even going up through the floor under the kitchen cooktop. Well, in any case, this is going to be a bit trickier than I’d thought to drill holes. The window idea might end up getting used after all. I could probably do that in a way that I don’t lose any more basement light than we’ve already lost with the driver vent taking one window pane.

I think using 3” vent holes will be far superior, enabling me to up-size if ever needed. With 2”, I could be revisiting this mess in short order.

Going out the foundation wall and digging on the outside of the house may be what the doctor orders here.

As is most of the eastern US right now, we are having some of the lowest temps in years. Lows below 10 F and highs below 20 F. I am wondering I the new boiler will be able to keep up.

And I see my electric and natural gas bill that’s due soon just came in at $713. That’s over $20/day. It doesn’t sound as bad when you hear we have an EV and $433 of the bill is natural gas (under $15/day) with two tank water heaters, 290k BTU of total potential. I am keeping an eye on things with my concept of replacing all that with only 155k BTUs. It will be interesting to see how things come in over the next two days.

I believe I should trust you guys here more than a YouTube short that YouTube fed me, but I believe this short provides information contradictory to what I believe I read here. Does a water softener help or hurt water heaters? Different for tank and tankless? I wonder how I should design my combi + (electric heat pump) tank setup.

ok. Data has come in for Tuesday and Wednesday, the coldest days we’ve had in years. I think I may need to take a look at the stove which we used only to cook rice both Tuesday and Wednesday, but I’m going to guess that spikes at 11 PM must have been from showers and the single 40k BTU water heater chiming in along with the heater. No temps get turned up automatically, and I’m unaware of any doors being left open at 11-12 PM Wednesday night. So the natural gas peak usage seems strange at that hour. Maybe my wife increased the temps? I may want to have something like the AirThings that I have in the basement that logs temps bc I don’t know a way to look at the setting history on my thermostats.

I had to do some research to figure out whether the ProTerra or Performance Platinum was the higher level model. It sounds like the ProTerra is the higher end only offering these extras:

• Leak Detection
• Auto-shutoff

You can buy the same energy factor, annual operating cost, and warranty duration for $200 extra. With this model, they just add a leak detection and auto-shutoff feature.

I guess I will have to figure out if either of those will benefit me or cost me any extra. In the 40 gallon size, it's $1700 instead of $1600. So, in not chinsing out, I guess I'd probably opt for the extra $100. It will probably be less after I apply a coupon when I ultimately buy too.

Rheem Proterra vs Performance Platinum - Which Water Heater is Better? (2025) | Today's Homeowner

The next thing to figure out is whether there's be benefit to a size any larger than 40 gallons. We have had two 40 gallon tanks at low temps and rarely ever ran out of hot water. Now that we are on a single water heater, I've bumped up the temp, also reading about legionnaires and wondering if we really should have had higher temps all along. Then there's the concept of either "mixing" or bypassing the water heater altogether when using the tankless inside the combi. All those things make me feel like a smaller tank might be more ideal as we are getting by with a 40 gallon natural gas tank in the WINTER, and in the summer hot water is needed less. There will always be the Combi having the ability to make hot water too if we end up in some scenario in the summer where the heat pump won't cut it. I understand they are SLOW though if you want to be efficient. So if we do not want to use the combi in summer and be as efficient as possible, a larger tank might be the only way to do it. So…
40, 50, 65 or 80 gallons?

3 showers, considering adding an outdoor shower and a basement full bathroom too. Two dishwashers. 4+ bathroom sinks, a bar sink, and currently 5 people living in the house. Even though one is off to college next year, we will still have occasions where everyone is home. We could turn on the combi DHW then though. So. Maybe 40 Gallons just to be frugal with the initial purchase… or just get a regular electric tank on FB Marketplace for $250 or less. There's a good chance that these heat pump water heater prices will come down even more as they become more standard.

No rush here but clearly making sure I have ventilation will be ideal.

I learned something watching Season 18 episode 3 of This old house. “Pipe thread wicking” for old pipe threads. In nearly 30 years of house work, i hadn’t used that but will be sure to add some to the tool box for when I try to tap into these old pipes.

Thank you for the comment. Would it make much difference if you knew that the plan was to only use it for summer hot water heating and just as a storage tank for winter hot water heating? That's my plan, as I'd like to use it as a dehumidifier / basement air conditioner in summer, perhaps with air-exchange with the kitchen above. But I assume the Combi functionality of the ModCon Combi boiler I've purchased will be more ideal for winter hot water. I guess there could be scenarios where we might want to have them both operational at the same time getting heat out of both, but if I can keep the kids from taking 60-minute showers, that would be ideal. I've read that it could be ideal to keep the kids bathrooms on a small tank with slow recovery and keep the master bath on an endless supply of tankless.

This diagram is the baseline for my plan to have a tank added to the tankless DHW.

Thanks for that. I see that in scenarios where water doesn’t move fast enough, you quickly get boiling that can be a serious pressure increase. I wonder if a setup could be created with a pressure sensor that would assure a pump goes nuts if the pressure gets high (enough).

But yeah. I get it. The hydronic is simply a way to enable the heat from the fire to go anywhere the thermostats need it, and reduce my dependence on natural gas. However, if using an outdoor reset, I guess it could be both good and bad if it would cause the boiler to not run bc the target temps get exceeded.

sorry I forgot to answer about the off-peak. We don’t have lower rates any time of day, but there is a “peak load calculation” or “peak load contribution” that can be up to maybe 25% of the bill and our delivery charges overall seem to be approximately equal to the cost we pay per kWh, like a $250 electric bill will likely be $125 of usage charges and $125 of delivery charges, probably including the PLC in the delivery charges. So we charge the Tesla Model 3 RWD (base vehicle with best mile/kwh) at night, just before we are scheduled to depart each day. Aside from no AC running, we used the electric heavily last month, even space heaters and some 1500 watt heat tape on the pool ice trying to assure it didn’t put pressure on the pool walls. It was $280 while the natural gas was $430, $710 overall. Coldest month we’ve had in the house.

In any case, I like the idea of having the electric on a timer, assuring it will not use electricity between noon and 8 pm, our peak hours.

I realized I’ve stalled, but I’ve been trying to get my basement organized before this next project really gets fired up. Sorry for the delay to anyone that might be following. Still deciding on exactly where to mount the new boiler in the basement. I’m not looking to try and make the change before warmer weather comes, where I might be able to go a few days without the boiler. I’m hoping the existing water heater and boiler can last. I will be quite embarrassed if they fail before I get this new boiler running.

I was looking at the gas lines and how I will be able to drastically simplify the gas lines in the basement and what will need to be capped. I think there’s going to be some significant demo that needs to be done in the basement to do this right. That also means cleaning up the garage so I can move stuff out of the basement and into the garage.