Indirect, Direct, Tankless

ewhit2220

I am about to finish a project to run natural gas to my house. I have a Peerless WBV boiler for the radiant heat and hot water with chimney venting that appears over 40 years old. I am converting the oil fired mechanism to natural gas for cost. I live in a 1500 square foot house with one bath and a half bath, but that may expand in the future. I have two circulator pumps on the boiler for two different thermostats for the radiant heat.

My goal is to split one of those thermostats and create three "zones" for the upstairs, downstairs, addition (Currently just addition and house zones).

My question is about the replacement of this boiler and the hot water. I am leaning towards an indirect fired hot water heater install with the current set up in anticipation of replacing the boiler and adding the third zone in the future. But the cost is quite different from a direct fired HE model. I don't know about tankless, but some people swear by them, but again, the cost is a lot more than direct fired.

Can someone help me think through the factors that I should consider and what I need to worry about when doing this? Do I need to upgrade the boiler to add the Indirect? Will a Indirect last substantially longer? Will there be any efficiency gains if I replace the boiler with a chimney vented model?

GGross

For me personally. I lived with a tankless, and it was only ever OK in my opinion, I do not prefer them so when it finally crapped out I replaced it with a standard tank style water heater, I also have a boiler and an indirect was definitely in the cards. I chose a standard tank style water heater as they are easy to deal with and readily available, if my boiler goes down I still can take a shower, if my water heater breaks down I can get a new one replaced in a few hours, with no disruption to my space heating. As for how long they last, most standard water heaters will have a 6-10 year warranty, most good brand indirects will have a lifetime warranty on the tank, so clearly the manufacturers put them at a longer service life, and I think most here would agree they last a long time.

Of the different options the only one I don't really want to live with is the tankless heater. I'm a fan of indirect fired, gas fired, electric, and heat pump water heaters though.

HVACNUT

Repipe the boiler correctly for 4 zones, with a 4 zone control panel for a future and an indirect. Don't add on. Do it right. A direct fired atmospheric will allow you to bathe in the dark if the power goes out, so that's a plus. Who doesn't like that?

What aquastat is on the boiler now? Is the chimney getting lined? Is it Triple wall?

Hot_water_fan

The decision in my opinion is: do I have space? If yes, then get a tank. Only if no, do you consider tankless. Anything a tankless provides, a tank can do better.

ewhit2220

https://forum.heatinghelp.com/discussion/comment/1824372#Comment_1824372

The Aquastat is a honeywell that would likley need to be upgraded if I did add the two zones. The chimney is lined for the current boiler. Based on the age and the repointing, I would say the liner is in good shape, but I can't really say, and I don't know about the type of liner/stove pipe.

ewhit2220

Tankless is out. I am fine with that, but with the cost being likely double or triple, is there any real savings that make the indirect worth it? Could it reasonably last for 40 years like a boiler? And if the boiler is not HE, then will I be better off just getting a HE tank model? Is there some way to work the numbers out to get the payoff period?

Hot_water_fan

I wouldn’t think of it like that. There is no payback unless you avoid 3 new heaters (by staying in the house for 30+ years). But you get more - a heater that recovers at a faster clip. You can also get that from a direct heater with a bigger burner.

Kaos

Around me the ROI on an indirect is negative (they are expensive to install and about same efficiency as a power vent), most houses with a boiler have a regular power vent tank or tankless water heater.

Tankless heaters are not bad as long as they have a buffer. A number of new units come with this built in, this solves all the annoying issues with them. If you don't have hard water, they are relatively low maintaince. Still not as low as a tank which you install and forget about for about 10-15 years when it might start leaking if you don't change the anode.

Some places have significant rebates for heat pump water heaters which makes them a much cheaper option. They tend to be the cheapest hot water as long as the install cost is reasonable.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1824387#Comment_1824387

except endless hot water, of course🤔

hot_rod

every type of water heating device has its pros and cons. Make a list of what you expect, see which matches best

Fuel efficiency

Upfront cost

Longevity

Required maintenance

Lots of hot water, or just a little

Endless hot water at 2 or 3 gpm

Space required

Venting requirements, combustion air

Fuel piping requirements

Rebates or incentives

Renewable energy use, PV or solar thermal

Keeping up with the Jones

Cutting edge or old school

Hot_water_fan

@hot_rod you know that a tank can supply endless hot water! The same folks that make tankless make tanks with huge burners. They also make tanks with smaller burners.

EdTheHeaterMan

I might add that water heaters are not rated like boilers and furnaces. They have a different rating system so you can't compare the burner efficiency of a water heater with a boiler. UEF as opposed to AFUE. I might add that the standard direct to tank burner with a standing pilot that vents into a B vent or chimney will offer you a 65 to 68% efficiency if you converted it to AFUE standards for comparison. That would be the water heater that will run without electricity. and be the least costly to replace when it starts leaking

When that water heater is connected to a chimney vent, that chimney will be pullong boiler room air (55° to 70°F) thru the 125°F storage tank 24 hours a day. that means the water heater burner may need to operate every 4 hours to recover the heat that was lost out the vent when no one was home to use the hot water. That is an inefficient way to store hot water in my opinion.

Now an indirect water heater can be connected to a home heating boiler that is up to 97% efficient. That burner can also be much larger than the one in the Direct Tank. So that tank will not loose heat out the vent because there is no vent in that tank. it is also super insulated so thattank can stay warm for up to 19 hours with no one using hot water befroe the temperature drops enough to bring the burner on to recover the lost heat in that tank. That means that if no one is using the water in the tank, the central heat boiler does not need to operate for 19 hours and that boiler can get as cold as the boiler room because there is no maintaining heat for the DHW tank. Finally that tank will lsr you as long as 3 direct tank heaters will. So the math is simple.

This spreadsheet does not account for inflation.  It is basic and simple.  Add up 30 years of water heaters and fuel cost and you can clearly see that the indirect is the best investment over time.  Since we can not talk about pricing on this site, the cost of the different water heaters are hypothetical based on my prices from 2016.    The fuel cost was based on a Rheem Energy Guide sticker from circa 2016.  

You need to put your numbers from the estimates and current fuel costs in that spread sheet and add about 2% per year for inflation in order to get a more accurate number.

Kaos

@EdTheHeaterMan

"Now an indirect water heater can be connected to a home heating boiler that is up to 97% efficient"

An indirect on a modcon at best is about 85% efficient during the heating season. The issue is return water temperatures are above condensing temp. Simply not possible to get it above 95 unless you are heating very large water draws where the entire tank is emptied out. Outside of the heating season efficiency is even lower because you need to heat the boiler and piping around it up each time which is lost energy. On two comparable triplex (similar water use) with indirect and tankless and summer gas use is about 40% less on tankless, so not even remotely close.

Overall, I would say it is at best about the efficiency of a power vented water heater.

Larry Weingarten

Hi, Just to muddy the waters a bit further, it is easily possible to get fifty years from a standard glass-lined steel tank. Just keep the pressure reasonable, give it clean combustion air (if fuel burning) and check and replace the anode as needed. 😇

Yours, Larry

hot_rod

https://forum.heatinghelp.com/discussion/comment/1824434#Comment_1824434

those large burner waters heaters like you see in restaurants don’t last long. I think they have 3 year warranty. Anything’s possible with enough fire under or in it