Looking for reasons not to size up indirect wh

thhn

Currently trying to decide between two Lochinvar Squire models - SIT050 and SIT065. Likely will be paired with a Noble boiler (not combi) - NKB110N. We have a tub to fill, and with 2 kids there may be times when my family is running 2 showers at the same time for an extended period. A larger tank would provide a buffer for that without sizing up the boiler.

So far, I can't think of any good reason not to use the larger tank and I'm looking either for confirmation of this or some other reasons not to. Seems like the heat loss is the same at ~390 BTU/hr.

Pros:
Extra hot water
Boiler cycles less (especially good in the summer)
Seems like a stretch, but the larger HX might mean lower supply temperature (less lossy, in theory) and/or be tolerant of scale buildup?

Cons:
Cost
With DHW priority, heat could be off longer while the tank is recovering (but the alternative is running out of hot water with the smaller tank!)

Any thoughts on this? Thank you!

pedmec

i would just do a sit050. set the tank temperature to 140 and use a mixing valve tempered to whatever temperature you need. 50 gallons at 140 degree water is plenty for two showers at the same time.

the boiler is a little on the smaller size for recovery purposes but with the mixing valve on the hot water outlet you have a buffer to play with. plus with a hot water demand the boiler supply temp will fire up to its max firing rate to get to its target temperature for the hot water loop.

although larger by 10 gallons and not an exact comparison i have a 60 gallon indirect with munchkin 199 with no mixing valve (my house was my lab lol) and had two showers plus a third right after within 20 minutes and never had any issues with temperature. that was with a tank temperature close to 130. if fact i use to marvel at how fast the boiler would shutdown after taking a shower. indirects are my first choice. but oversizing is just taking up space

hot_rod

Start with how much hot water you actually need or want. How much does the tub hold? What type shower heads, how many gpm
Use profile, all baths and showers after one another?
Folks tend to pattern their use around the DHW and recovery available in some cases.
If you want endless DHW, maybe a tankless so a better fit?

Paul Pollets

I'd go with the larger indirect. Some install an anti-scald valve on the outlet and keep the tank at 140. This kills all legionella and gives the tank 20% greater capacity.

mattmia2

Given the description of children if you are in a climate where you get around 35 degree supply water temps I would think about an 80 gal.

Larry Weingarten

Hi, If it’s a glass lined tank, the action of the anode can cause smelly water if the volume of the tank isn’t turned over pretty much daily. So, if there is no anode, a larger tank is good so long as it has good insulation.
Yours, Larry
Ps. Using a powered anode prevents the odor problem.

EdTheHeaterMan

Seems like there is no consensus. @pedmec says 50, Paul says 65, Hotrod Bob says Tankless, and Larry says the water is going to stink anyway.

Almost makes you want to take cold showers!

Hot_water_fan

Ha another perspective is that probably 95-99% of American families don’t have indirects and are just fine. 

hot_rod

EdTheHeaterMan said:

Seems like there is no consensus. @pedmec says 50, Paul says 65, Hotrod Bob says Tankless, and Larry says the water is going to stink anyway. Almost makes you want to take cold showers!

The post indicated the decesion  to go larger had already been made, Nice that he was offered options not just validation. I suppose😗

pedmec

everybody is discounting the recovery of the indirect. it will recover just as fast as you use it. properly sized circulator and you will never have to worry about taking a cold shower, that's the main advantage of an indirect. that and the lifetime warranty is why your paying all that money.

In_New_England

Hot_water_fan said:

Ha another perspective is that probably 95-99% of American families don’t have indirects and are just fine. 

What, really? Like most have on demand, or most have a separately powered hot water heater?

hot_rod

pedmec said:

everybody is discounting the recovery of the indirect. it will recover just as fast as you use it. properly sized circulator and you will never have to worry about taking a cold shower, that's the main advantage of an indirect. that and the lifetime warranty is why your paying all that money.

Good point 500.3.(120-55)= 97,500 BTU/hr required. Basically 2.75- 3 gpm is what you could expect from a 110,000 combi also. A tub fill is probably closer to 105- 108° fill so some cold is blended in.

A tub valve with flow exceeding 3 gpm would drag the indirect down, but you have the dump capacity to use up first, as the boiler is recovering maybe 3 gpm..

So an exact answer would require incoming water temperature, desired final temperature, flow rate. Plug it into the universal hydronic formula for a close answer. I think 40 and 50 gallon suit most US households, and with only a 35,000 BTU/hr input on fossil fueled or 15,000 BTU/hr on a 4500W electric.

Funny thing about DHW, families use up exactly what they have available whether it is 30 or 119 gallons

Hot_water_fan

@In_New_England most Americans don’t have boilers period. So tankless or tanks. 

In_New_England

Hot_water_fan said:

@In_New_England most Americans don’t have boilers period. So tankless or tanks. 

How do these 95%-99% heat their homes?

thhn

hot_rod said:

Start with how much hot water you actually need or want. How much does the tub hold? What type shower heads, how many gpm
Use profile, all baths and showers after one another?
Folks tend to pattern their use around the DHW and recovery available in some cases.
If you want endless DHW, maybe a tankless so a better fit?

Not endless, just enough. But I'm sure the rest of the family wouldn't complain about endless! As you said, we'll likely use what's available so perhaps I should downsize the tank, install low flow shower heads, and save some money

Thank you all for the input, some information missing as many of you indicated. The incoming water temperature is ~47 degrees. I'm expecting ~2.5 gpm out of the boiler with a ~70 degree rise, enough for one shower (or using the washing machine). Standard shower heads, currently 2.5 gpm each (and one per shower). The tub holds 45-50 gallons.

EdTheHeaterMan said:

Seems like there is no consensus. @pedmec says 50, Paul says 65, Hotrod Bob says Tankless, and Larry says the water is going to stink anyway.

Almost makes you want to take cold showers!

And one vote for 80! I'm glad to have the variety of perspectives, no matter which I end up choosing I'm sure I'll end up making a more informed decision as a result.

pedmec said:

everybody is discounting the recovery of the indirect. it will recover just as fast as you use it. properly sized circulator and you will never have to worry about taking a cold shower, that's the main advantage of an indirect. that and the lifetime warranty is why your paying all that money.

I did factor this in, but putting it as "the worst case scenario is you can only take one shower at a time" makes me worry a little less about sizing the tank perfectly.

GGross

In_New_England said:

Hot_water_fan said:

@In_New_England most Americans don’t have boilers period. So tankless or tanks. 

How do these 95%-99% heat their homes?

in the US it's mostly forced air.

Hot_water_fan

@In_New_England

i wasn’t clear- not all homes with boilers use indirects. Boilers are the minority to begin with: most US homes use forced air, so furnaces and/or heat pumps, which don’t pair with indirects. Indirects, while great, aren’t typical. 

Zman

A couple of questions come to mind:
What is the capacity of the tub?
What is the flow rate of the tub valve?
Do you wish to maintain a hotter tank temp because of concerns about legionella and other organisms?
Do you need a mixing valve to prevent scalding?

Filling the tub is going to be your biggest issue with any tank. If your flow rate exceeds the boiler output capacity for an extended period, there is an excellent chance you will run out of hot water going with a smaller tank and/or no mixing valve.

Mixing valves require maintenance but will increase your effective storage with any tank size. If you have young kids or elderly folks living in the house they are an excellent idea.

On the efficiency side, it is worth pointing out that higher tank temps will have higher standby losses. The larger tank will often have a coil with more surface area, this will increase boiler efficiency slightly because the boiler will be able to run at lower return water temps.

Good luck convincing the spouse of this one but, filling the tub more slowly (or secretly throttling the supply to the tub valve) will also alleviate the problem. Personally, I have accepted the loss on this one, it is way easier to put in the bigger tank. It is also easier to replace the brake pads and rotors every 30k miles than it is to have the "downshift" conversation .

In_New_England

Hot_water_fan said:

@In_New_England

i wasn’t clear- not all homes with boilers use indirects. Boilers are the minority to begin with: most US homes use forced air, so furnaces and/or heat pumps, which don’t pair with indirects. Indirects, while great, aren’t typical. 

Ah of course! You and @GGross are right! Here in the suburbs of Boston, with a lot of neighbors and friends living in older/smaller/non-renovated housing stock, I've gotten used to baseboard heat, but in other parts of the US, and newer housing, people have ducted systems with furnaces.

mattmia2

Zman said:

It is also easier to replace the brake pads and rotors every 30k miles than it is to have the "downshift" conversation .

It is also easier to replace pads and rotors than to replace a clutch weather it be inside or outside the transmission so it isn't entirely clear that downshifting is more economical.

Zman

mattmia2 said:

Zman said:

It is also easier to replace the brake pads and rotors every 30k miles than it is to have the "downshift" conversation .

It is also easier to replace pads and rotors than to replace a clutch weather it be inside or outside the transmission so it isn't entirely clear that downshifting is more economical.

In this case, it is an automatic transmission driving down long grades in the mountains, the kind with runaway truck ramps (that get used regularly ). As for manual transmissions and clutches, clutches really only wear when engaged and disengaged. Starting from a stop and resting your toe on the pedal is when wear occurs. Brakes have limited ability to dissipate heat, especially over long periods of time at high altitude where there is less air density to move it away from the source. The engine and transmission have much better cooling systems. As a trucker friend of mine wisely says "gears are for slowing down, brakes are for stopping..."

hot_rod

Zman said:

It is also easier to replace the brake pads and rotors every 30k miles than it is to have the "downshift" conversation .

It is also easier to replace pads and rotors than to replace a clutch weather it be inside or outside the transmission so it isn't entirely clear that downshifting is more economical.

In this case, it is an automatic transmission driving down long grades in the mountains, the kind with runaway truck ramps (that get used regularly ). As for manual transmissions and clutches, clutches really only wear when engaged and disengaged. Starting from a stop and resting your toe on the pedal is when wear occurs. Brakes have limited ability to dissipate heat, especially over long periods of time at high altitude where there is less air density to move it away from the source. The engine and transmission have much better cooling systems. As a trucker friend of mine wisely says "gears are for slowing down, brakes are for stopping..."

With automatics you should be able to pop down a gear, at least out of overdrive? My Toyota has a button right on the shifter for downhill mode. My Ram Cummins has an exhaust brake for downhill work, great for trailering in the mountains.

EdTheHeaterMan

Looking for reasons not to size up indirect wh is the title of this Discussion. And now we are debating wether to downshift based on the type of transmission you may have in a Toyota. WOW! Did this go off topic

My 1923 Ford has a 3 speed transmission that utilizes planetary gears according to the Ford Literature. The thing is that one of those three speeds is reverse. So only 2 forward gears.



I dare you to go more off topic that that

hot_rod

EdTheHeaterMan said:

Looking for reasons not to size up indirect wh is the title of this Discussion. And now we are debating wether to downshift based on the type of transmission you may have in a Toyota. WOW! Did this go off topic

My 1923 Ford has a 3 speed transmission that utilizes planetary gears according to the Ford Literature. The thing is that one of those three speeds is reverse. So only 2 forward gears.



I dare you to go more off topic that that

Can the driver drag their feet like the Flintstones, to brake?

I think the OP got plenty of indirect input here.
Many posts go off the track here:). How else would the braking discussion come up.

mattmia2

hot_rod said:

Can the driver drag their feet like the Flintstones, to brake?

His brakes are canvas. or were.