Replacing Boiler and Indirect Tank - Northern, IL

user1234

Hello everyone,

I own a house built in 2002 and it has a peerless PF140-N rev 2 boiler paired with a Weil McLain 50 gallon gold plus indirect fire water tank.

im replacing both the boiler and the water tank. Long story short, I run out of hot water constantly, and the peerless unit has been a royal pain in the butt since we moved in less than 2 years ago.

There are three of us living here but the house has 4 full bath and a radiant in floor heating system that covers a 2600 sqft basement and 800 sqft garage, 3400 sqft total.

I have done a ton of research on this but this is my first home I’ve owned with a boiler so it would be great to get feedback on the following:

1. which boiler and indirect fire water tank tank would you recommend? Manufacturer and model please!
2. I’m not interested in a combi unit.
3. Is it possible to use a tankless water heater in place of the indirect tank and use a boiler for radiant floor?
4. Based on the photos, some of the quotes I’ve received, I’m being told that the piping, pump, switch setup I have is not ideal. Is it worth modifying? I can supply more photos on request.
   
   Thanks,

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hot_rod

Does the boiler heat all the spaces adequately on the coldest days? that is one way to determine if it is sized correctly for the heating side.

You need to define how much DHW you need to adequately size a HW tank. That boiler and tank, properly piped and controlled should provide plenty of HW, unless you have some unusually high loads? A large soaking tub perhaps that drains the tank? High flow shower heads or body sprays?

In all cases you need to size the boiler to the largest load. Most often that is the heating load. In some cases the DHW load is larger and the boiler needs to cover that.

Bottom line, knowing the heating and DHW load is the path to a system for your exact application.

mattmia2

You need to define how you use hot water first. Are you using more than one shower simultaneously? Are you using any of them sequentially or both simultaneously and sequentially, do you just use each one once or are multiple people using the same shower sequentially or several of them at the same time sequentially?

You have enough hot water to use each of them sequentially or possibly 2 at a time. You have nowhere near enough for all 4 at a time.

Are you running a washing machine or dishwasher at the same time?

It could use an instantaneous water heater too but you need to answer how you use water first and since it doesn't store hot water it needs a big enough gas supply to heat all that water as it is used whereas with an indirect you can buffer it with a large storage tank. If it is more than 1-2 simultaneous showers then you probably are looking at multiple cascaded instantaneous water heaters.

user1234

Hi Bob,

1. the boiler does heat all of the spaces adequately on the coldest day. Although sometimes when it was really cool outside, the boiler would have a fault and need to be reset. Part of the reason why I’m replacing it.
2. I have very large soaking tubs ~ 80 gallons and the water fixtures I have are not flow restricted and I estimate them at 2-3 gallons per minute for the rain shower heads in three of the bathrooms.
3. With radiant heating, my understanding is that the DHW would override the radiant heating for the small amount of time we are showering or filling the tub. Does this sound right to you?
4. I forgot to mention that the piping we have leaving the current boiler is either 1” or 1.25” and some of the technicians are saying it should be 1.25” or 1.5” when connected to 100,000 to 150,000 btu boilers.
   

Thanks for taking time to respond. Do you have enough information to make a recommendation now? If you have any other questions, please let me know.
-T

user1234

hello Mattmia2,

1. we sometimes shower at the same time and I estimate our GPM usage while both showering at ~ 6 gpm on the high side. The current setup can’t keep up for more than 15 minutes of total usage so we just take quick showers to both have hot water.
2. I’d like to size things for two people showering simultaneously while also using a washing machine and dishwasher. The dishwasher is a Bosch 800 series and it uses very little water. Also, we mostly use cold water while using the washing machine.
3. with my old house I installed a Rinnai 10 or 11 gpm unit and it is still working perfectly while providing water for two showers, dishwasher, and washing machine. The tech quoting us the tankless system for DHW prefers AO Smith.

is this enough to go off of? What are your thoughts?

Kaos

Assuming all plumbed properly and the indirect on priority, most likely your indirect has a busted dip tube. When this happens, cold water is mixed with the hot near the top and capacity is reduced. The original installer could have also mixed up the cold and hot water feeds to the indirect, would cause similar issues. I would check this first before spending money on replacement/alternative.

Lot of the AO condensing units are rebadged Tagaki ones, those are good tankless units.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1849718#Comment_1849718

100,000 btu and a 40 gallon tank is not remotely enough to cover the desired usage at the 80f or 90 f rise that you would have in the winter in IL.

The GPM stated on tankless unit advertising isn't at anywhere near that temp rise. A 200,000 BTU output at 80 f delta t is 5 gpm.

Kaos

100k gets you about 3GPM continuous which is good enough to run a shower non stop. You still have the stored 50 gallson of water in the tank at around 140F which when mixed down to 100F shower, is good to run another shower for about 20-30m. Possible to run out, but not likely if system is working properly.

You also don't need 90F rise. Water there is probably similar to ours which is close to freezing in the winter, around 40F. Shower water only needs to get up to 100F to 110F, so 60F to 70F delta. Even if you are making 140F water, it gets mixed down at the shower to lower temp so the effective rise is still the same.

Jamie Hall

You have a remarkably heavy domestic hot water usage, honestly. I'm not at all sure that either an indirect or a normal sized tankless will handle your usage. Two shower heads of the size you mention are around 300,000 BTUh total load — well over your current boiler's capability.

One option would be large tankless heaters for each bathroom; you will need at least 150,000 BTUh capacity for each. Since there may be two or three operating at once, the gas supply to the building may need to be upgraded.

Another option would be a much bigger indirect. I would estimate you need around 160 gallons. If you could find one…

A third option would be conventional direct fired tank type gas water heaters; each bathroom would probably need around a 120 gallon unit to handle the load.

user1234

thanks everyone. If we size for 4 to 5 gpm (1shower operating continuously) will a ~ 150,000 btu boiler work?

I am only replacing the single peerless boiler with a new boiler. Given the above scenario with 4-5 gpm DHW, is it better to go with a boiler with indirect tank or a boiler with tankless?

Jamie Hall

No. You need at least a 200,000 BTUh boiler in that scenario, if you are keeping the 50 gallon indirect — assuming that the indirect can handle that much power. I haven't looked that up.

And that boiler is almost twice as big as what you need for your heating load, which will lead to problems and inefficiencies on the heat side…

Not to put too fine a point on it, you have a commercial level domestic hot water load; you need to treat it as such. "Normal" residential units just aren't going to do.

user1234

Thanks Jamie. So if it were your house would you ditch the indirect and go for a tankless for DHW and size the boiler just for the radiant floor heating?

Jamie Hall

I'd check my gas line sizing, and then if I had enough I'd get a good mod/con sized and controlled for the radiant floors and a gas fired tankless for each bathroom, sized to that particular load — maybe use one of them for the kitchen as well.

hot_rod

A simple formula for tankless sizing

500 X flow X temperature rise

500 X 5 gpm X (120°- 55°) = 162,000 btu/hr.

So a 180- 199,000 tankless to supply continuous 5 gpm.

So either you store enough DHW to cover those dump loads, or make it instantly with a tankless.

Modern shower heads are more in the 1.5-2 gpm range

Larry Weingarten

Hi, A couple more thoughts. If you installed lower flow showerheads, the equipment capacity problem would go away. That would be the simplest, least expensive fix. Another approach is to install shower drain heat exchangers. These can capture up to around 60% of the heat going down the drain, and put it back into the shower, essentially cutting the hot water demand by around half. Something about having one's cake and eating it… 😏

Yours, Larry

Kaos

No need to guess. Get a 5 gallon pail and stop watch on your phone. Turn on each shower and measure how long it takes to fill the pail. If you fill in 2 min, the shower is flowing at 2.5GPM.

If you have larger tub, also clock the tub filler there the same way.

If your total shower flow rate is around 4-5GPM for both, your existing setup should be good enough, so if you are running out there is an issue with your setup. Usually you can fix it at much less cost than a new install.

As a reference, I have a triplex with a shared 50gallon 50kbtu gas water heater. The place has regular shower heads (stock Moen or Pfister stuff) and the tank never runs out and that is much less oomph than your setup.

mattmia2

Is the tank setpoint higher and mixed down with a thermostatic valve? if not the tank will reach a cooler equilibrium after a draw for a while.

I would do it with a large indirect or multiple large indirects.

Another option is to put an indirect at each bathroom and feed all from the boiler. If you do that right you can get hot water quickly without the recirculation.

user1234

Good evening everyone. I tested the flow rate of all of the fixtures of the main bedroom.

Rain shower head - 5.5 gpm

Standing tub faucet - 4.8 gpm

Regular shows head - 3.5 gpm

Detachable wand - 3.0 gpm

Given this information, does it make more sense to go tankless for DHW and boiler for the radiant?

kaos and I were in the same wavelength. I got the 5 gallon bucket out! 😂

user1234

hello Mattmia2, I have messed around with the dial that changes the temperature for the indirect. It really doesn’t do much so I leave it set in the middle.

thanks for the recommendation on the lower flow rate heads Larry. It still won’t help with my 80 gallon Kohler jet tub. It’s such a pain in the butt to have to wait half an hour to fill it completely. I can look into shower drain heat recovery but that sounds like it might be better for when you do a bath remodel?

I think Kaos might be right about the busted dip tube. I’ve always thought the tank was the main issue. But it’s funny when I watch my boiler with the bath faucet water turned on only (4.8gpm) it shows the percent available going down and it is unable to keep up. Hence why I am unable to fill the 80 gallon kohler jet tub up all the way.

I think I’m leaning toward one or more tankless for the DHW given the crazy flow rate these fixtures have.

Im on well water as I don’t believe I mentioned that previously.

mattmia2

Well water is usually a bit warmer than municipal water in the winter. Municipal water in the great lakes usually comes out of a river or lake and is buffered in above ground tanks so it is in the mid to upper 30's at the coldest times of year. well water tends to be around 50.

Kaos

That much flow you need two 199k tankless units if you want to run both showers at the same time. That is a big gas service. You can shave some of that off if you have the space to install drain water heat recovery but it still won't get you down to a single tankless. I think the more cost effective option would be to install a larger indirect or add another 50gal in parallel with the existing one. Run the tanks extra hot and use a mix vale to bring the output down. The boiler can stay the same. You could still run out if you have take long showers, but would work for typical use.

A simpler option is to get some better showerheads. Something like this, many others out there:

https://www.grohe.ca/shower-heads/stick-shower-head-1-spray-95-l-min-25-gpm/grohe-chrome-27705000

Not sure what your water costs are, I'm not in the land of water shortage, but even here switching from 5.5gpm to 2.5gpm would have a pretty quick ROI.

mattmia2

Can you show us a picture of the dhw piping to the indirect? it should have a thermostatic mixing valve and be stored at a higher temp in the tank. This only gives you maybe 10%-20% more capacity but it allows the temp in the tank to fall as the thermostat makes a heat call and the boiler heats up which all takes several minutes before the boiler starts heating the tank. the thermostatic valve keeps the hot water temp constant as the temp in the tank falls.

user1234

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Jamie Hall

All this effort is very fine, but… the bottom line here is that we have at least one 5 gpm shower head, and I dare say that our OP likes it. That 5 gpm showerhead, with a nice 15 minute shower, is 75 gallons of hot water. Let's say at 110 so it's really nice.

Now well water is likely to be at 40, so we have a 70 degree rise if we want to make that from well water directly. But let's be optimistic and say that at the beginning of that shower we have 50 gallons of water at 110. We still have to make up an additional 25 gallons in that 15 minutes. That's still, going to be a lot of heat — and it does nothing for the next person in line, who wants another 15 minute 5 gpm shower.

The only way I can see to do this given the fixtures and use profile we have here is big, single bathroom group instantaneous heaters — or a stoage tank or tanks big enough to handle the shower (or the hot tub — the volume is about the same). Which is on the order of 80 gallons per bathroom group.

One of the minor objectives is to meet the client's needs — and this is what @user1234 wants and needs. And, honestly, I sympathise with him. It's all very fine to talk low flow shower heads and Navy showers, or forget the hot tub for the wash bucket — but if that's not what you want… and you can get what you want… have at it. It happens that my tank type water heater has a recovery rate of 2 gpm. I wish it were more…

mattmia2

Is that mixing valve in the 3rd pic for the dhw or making the low temp water for the radiant? It looks like it is in the heating loop.

when it "runs out" of hot water do you still get warm warm water if you turn down or off the cold water?

filling the tubs you either need a big indirect that can hold enough water to mix with cold to the desired tub temp or a big instantaneous water heater or 2. might look at commercial instantaneous water heaters.

user1234

https://shorturl.at/KjLaW

the above link is to a short video I put together.

Jamie is correct. I love my 5.5 gpm rain shower head and since I’m on a well and live 2 miles from Lake Michigan, I pretty much have free water except for the cost to pump it out of the ground and heat it.

im looking at a significant investment of 10 - 20 k so id like to have a minimum of 5-6 gpm of DHW available all of the time and be able to fill up these massive jet tubs with 105 degree f water.

mattmia2 the mixing valve in question is only for the radiant heating.

hot_rod

What is you water pressure? Reducing pressure reduces gpm also. 45- 50psi is plenty, but we see 80- 100 psi in some un-regulated homes.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1849853#Comment_1849853

On a well? I'm going to bet swinging 30 to 50 psig. Maybe 40 to 60. At least I never set one higher than that…

Kaos

If you are looking to run at 5.5GPM, a single 199k tankless will work.

I would plumb it before your existing indirect and set the temp on the tankless a bit higher than the indirect. This would get you a couple of things. A condensing tankless is about 15% more efficient than the indirect, the tank buffers the cold water slug from the tankless and you now have the combined output of both. This means you can run both showers at the same time pretty much indefinitely.

Tankless units don't like hard water, something to watch.

Karl Reynolds

The thermostats on those tanks are known to fail, especially if they get wet. It doesn't appear that there has been any water dripping on it, but besides the dip tube, that would be a hot button item to check.

Jamie Hall

"This means you can run both showers at the same time pretty much indefinitely."

It would be nice to think so, but I beg to differ. You'd need a heat input of 350,000 BTUh net to do that, and a boiler that big would be insane. You could, yes, in principle do it with the existing boiler — or a similar replacement — and a 250,000 BTUh instantaneous unit, assuming the boiler and indirect controls were hot start.

But… why? I'm still in favour of two 199,000 BTUh instantaneous units, one for each bathroom group with one also handling the kitchen, or (on second thoughts here) two 120 gallon tank type water heaters, preferably gas fired, again, one for each bathroom group. The choice really would be determined by the gas supply capacity to the house.

Kaos

Jamie,

I was suggesting the 199k tankless in series with the existing 50gal indirect. With a 100k boiler on priority, you get near 300k out of the combined setup plus you still have the tank volume as backup.

The one issue might be the pressure drop across the tankless at 9GPM will be pretty high, so that might be the limit. Instead of series, you can also tie the tankless and indirect together using a mix valve which would reduce the pressure drop.

mattmia2

5 months from now they will be posting about how their well ran dry.

Jamie Hall

Why oh why are we fighting this? Our OP wants 10 gpm for a shower, or perhaps 80 gallons for a tub and 5 gpm for a shower… say 75 gllons.

Even if the 50 gallon indirect can handle and transfer — at that flow rate — all 100,000 BTUh from the boiler, you're still at least 10 percent short. And you don't have to be.

And on the well… depends on the well. The deep well for Cedric's home was tested for 72 hours straight at 20 gpm (about 14,000 gallons per day) when it was drilled, although the pump which is in it is only good for 10 gpm. But they do vary. A friend of ours a couple of towns over has a 300 foot well which is only good for a whacking quart a miniute… 400 gallons per day. He's pretty careful about how he uses water!