New High Eff Gas Boiler

StefK

Hey All..

Trying to find the best replacement for my old boiler...Two quotes so far have been for Buderus 142 and the Lochinvar 105 any suggestions. I am worried about the aluminum heat xchanger

HomeOwner1

Happy with our Navien Combi so far

Depends on the size of you place.



We have a Navien Combi boiler which also does hot water. It is much less expensive then other options we priced out. It just has not been out for 20 years yet and their initial models with an aluminum exchange was not so good. Now they only sell their stainless higher end unit. Ours is very efficient and works really nicely.



Heard good things about Triangle Tube as well. They were not enough to meet our hot water needs for 3 bathrooms though, hence the Navien. Depends on the size of your place.



If you go Navien, make sure your installer knows how to install it correctly. Also, get the outdoor sensor as well.



Ask around with folks that own them and get their opinions.

Zman

Application

I am personally a big fan of the firetube heat exchanger that triangle tube introduced and is now being offered by lochinvar and others.I share your concern about aluminum. The problem seems to be worse with certain water conditions.

There are some applications where the combi units make sense. The issue with instantaneous combi boilers is that once you size the boiler for your Domestic water needs, you are extremely oversized for your heating load. This is bad for efficiency and maintenance.

The triangle tube prestige excellence combi and the new viessman combi have internal tanks which require less BTU's for domestic water.

I would find a company that is willing to do a heat loss calc on your home and evaluate you domestic water needs to get you the right product. Sizing and installation are very important.

Carl

HomeOwner1

Turn Down Ratio for Combi units

If you look at combis, the turn down ration is important.



Running the hot water side takes more energy. Then switching back to heat uses considerably less. Our particular Navien 240kBTU unit for example, goes from 199k all the way down 20k with pretty good efficiency on the heat side. Assuming you have the modulation temp sensor hooked up. That means on cold days you may run your loops at 180 degrees whereas on somewhat warmer winter days, a slow steady burn with 130 degree loop temps will do just fine. Then the unit can dial down its heat provided to a slower and less energy steady burn. So on these modulating units, they are a bit more forgiving on sizing.



Some of the other units like Triangle Tube don't offer such a large turn down ratio, hence you may not meet your hot water needs with them. Its too bad they don't make a larger hot water capacity on their units.



The hot water flow at the coldest day in the year is also another factor. The combis lose pressure the colder the input water temp. SO if it has to raise the temp 77 degrees, it may only put out 5.5 gallons per minute (ex. a low flow shower head is about 1.5). In the summer you would get maybe 11 gpm since the delta of temp is much less. The Triangle tubes and others usually have much lower flows. They have buffer tank, but that is only for a limited set of gallons, then the pressure drops (ex. what the sales brochure does not tell you!). We had a salesman pushing us really hard on a Champion and trying to convince us three people could all shower at the same time in the dead of winter. Triangle Tube support disagreed with his analysis. We appreciated their honesty.



From what we learned, the combi units are sized on domestic hot water first, then checked to see if your heat loss properly falls within the efficiency range of the turn down envelope. We have a properly sized unit and glad we did the homework with the advice of many good professionals and learned what advice was bad as well.



Make sure your installer sizes it correctly. Lots of factors to consider to choose wisely.

Zman

Instantanious

Instantaneous heaters will never be as efficient as those with a tank. There are so many short cycles from all the small draws of water. Every time someone fills a glass or washes there hands the boiler is short cycling. It is rare that you need 200K/BTU over a long period of time. Keep in mind your typical  electric water heater only produces about 17K/BTU. It can do this for one reason, storage.

A boiler with a tank  will always run long efficient cycles if it is sized and installed correctly.

I have asked both Triangle and Viessman about high turn down ratios. Both companies have deep roots in Europe and are leaders in condensing boiler technology. Both companies say that efficiency drops significantly at high ratios. I mentioned that other companies are claiming 20 to 1. They just smiled and asked if they have DOE tests to support the efficiency at those ratios.

I have no idea where homeowner one lives, ground temps do not vary much between summer and winter. Maybe 10 degrees? I can't follow the thinking where the delta t in the Summer is 1/2 what it is in the Winter.

Carl

SWEI

Effeciency and payback

I'm with Carl -- show me the efficiency curves.  A properly sized modulating boiler running on outdoor reset spends the overwhelming majority of its time firing at the lower end of its range.  In purpose-built condensing boilers, this also delivers the highest efficiency, maximizing return on the investment.

Gordy

Lochinvar fire tube

Is a swish. Excellent controls

HomeOwner1

In New Jersey

Yes, I would imagine that incoming ground temps probably don't vary that huge of a range as well. Agreed.



Those are probably extreme climate examples. We don't get Alaska winters over here!

gennady

Home owner

In regards of your intention not to give up I remember one girl saying about a man who stocked her, it is better to give up than fight.