Tankless boiler efficiency?

[dbuck50]

I have a 6 year old setup with a oil fired Weil-McClain boiler that is also a tankless water heater and it has a power vent exhaust.

I have hydronic heat and even though the heat isn't used in the summer, of course the boiler is running for the hot water.

I am wondering if this setup is all that efficient in regards to oil use. Would I be better off with a separate boiler and hot water heater? or an indirect water heater?

My motivation here is that I would have the boiler replaced with a Boderus direct vent so that I can get rid of the noisy power vent. If there were additional heating oil savings that would help motivate me too...plus I figure the existing boiler is still worth something since it is only 6 years old (WGO Gold I think).

I live in upstate NY if that helps. Thank you in advance for any advice.

[dbuck50]

I forgot to add that I have what seems like and endless supply of hot water now with my system. The hot waters needs are only for my wife and I.

[aemeeich]

An indirect water heater coupled with a cold-start boiler will be much more efficient than a tankless.

With a tankless setup, the boiler needs to stay warm all day long. With an indirect, the boiler only fires when you use hot water from the tank.

An indirect water heater can be added to your existing boiler, and the controls changed to make it a cold-start. A Buderus boiler will have slightly higher efficiencies (only 1%), however, since the W/M Gold already is a high efficiency boiler you won't ever save enough to make a complete swap-out worthwhile.

Michael

[dbuck50]

Sounds interesting and thanks for the response. When you say cold start, does that mean that hot water is in the indirect fired tank, gets cold and only when it needs to get used does it get heated up?

[johnsp]

Yup, that's right. But most oil fired cast iron boilers like to stay warm. If the boiler cools to room temp durring the day, then heat backup to 160° to re-heat the indirect, that's a lot of flexing and wear and tear on the rubber seals betwen the cast iron sections. Plus condensation can start to form inside the boiler. Soot might start caking in the boiler also as it fires cold.

You might save some oil by allowing the low limit of the boiler go to 120° instead of sitting @ 160° all day long.

Now one is going to give you anything for a used boiler so it seems a shame to replace it already.

[dbuck50]

OK, maybe replacing it now seems a waste (even though I would like the direct vent vs. the power vent).

But it sounds like shutting off the tankless part and using a indirect fired would be a happy medium? is the fuel savings worth the wear on the boiler from going from room temp to heating the hot water in the summer months?

Still sounds like my current setup isn't very efficient. I am guessing this type of system exists for lower cost installs/setups? Would there ever be a good reason to go with my current setup other than cheaper setup costs?

[casturbo]

Your setup is the right one for you. Indirects are for high capacity usages, they save very little, if anything, over a tankless setup in a low demand application. And the indirect HWH is very expensive to install so you'll never see the payback. You got the one of the best domestic boilers money can buy, if the power venter is bothersome, install a conventional chimney. The direct vent Buderus is loud as hell, as any oil fired machine would be. If it's quiet you want without any hassles, the chimney is the solution. No expensive and unplanned repair costs with a chimney either....said another way, power venters suk.

[dbuck50]

Thanks.

So I have heard 2 opinions on efficiency...one is that cold start boiler with indirect WH is MUCH more efficient than tankless boiler/heater. And another that it ISN'T more efficient unless you have high and long hot water demands.

I am surprised to hear that a direct vent boiler is as loud as a power vent one though.

Anybody else able to weigh in?

[johnsp]

A direct vent should be quieter. Usually there's no barometric damper and the burner gets a fresh air box that also muffles the burner noise. A 3 pass boiler like the Buderus will also be quiter since it has extra insulation and the 3 pass heat exchanger helps control noise. But don't expect the few points of extra efficency to ever pay for the cost of a new boiler.

If you have natural gas, any thought to installing an DV instant tankless water heater and leave the boiler just for heat?

The WGO was never rated as a DV boiler, so I wouldn't try to put a balanced flue burner on one.

[dbuck50]

OK, so I think I am sticking with the existing boiler and maybe a chimney, but would it be more efficient to run an indirect heated water tank vs. the current tankless boiler?

[Noel Murdough]

with the correct control and settings.

Noel

[johnsp]

You have to weight out the costs. A new chimmney might cost moe then getting a direct vent boiler.

[dbuck50]

Well, chimney costs aside and assuming I'm keeping the Weil-McClain. What type of efficiency could I expect by running the boiler cold start with a indirect fired water heater. I am asking this in terms of reduction in oil use. Would it be roughly 5%, 25%? I live in upstate NY and its just my wife and I, so there aren't massive demands on hot water.

[casturbo]

Running a boiler with cold start may save a few dollars a month, BUT you'll give all of that back and then some once the boiler gets loaded with scale from being left cold for long periods of time. A dirty boiler consumes lots of fuel. The cost of a quality indirect HWH will change your mind, trust me.

[Leo]

Ok,

I work for an oil company and we install Direct Vent Buderus boilers. On a chimney they aren't so bad, direct vent they tend to be problems. A Buderus boiler can only have an Indirect WH they have no provision for Tankless. Direct vent is the most quiet.

The Weil McLaine Gold likes warmth but if you got an indirect you could have it turned down to about 120 degrees as someone else said. Today's indirects have very low losses. Power Venters fail every three to five years, they are a mechanical device working under high temperatures and affected by the products of combustion.

My opinion is any fuel has products of combustion and a chimney gets them away.

Hope this helps,
Leo

[hydronicsman]

Go indirect w/ cold start. The boiler will fire enough to keep it dry. Your Gold is poor insulated compared to an indirect's 2-3" of R.

Why have the thing maintain temp, and lose it, when it's not needed? Like having your car idling in the driveway all night in case you MAY want to drive it?

[Leo]

Weil Golds tend to get dirty on Cold Start. What's cheaper, spending extra to get it cleaned and using extra oil heating a dirty heat exchanger or using a little more oil keeping it warm and having less of a maintenance issue. He stated it is he and his wife so in warm weather that indirect won't call often hence the boiler gets much colder. I base my statements on doing service and annual tune ups and seeing what is cleaner and what isn't.
If this guy were to use more oil I wouldn't benefit from the sale so I am not trying to sell oil. I am an advocate of conservation.
Leo

[bigsandy]

There is a reason why Buderus is one of the only boilers sold in the U.S that does not have a tankless boiler.

Tankless heaters will not keep up with the hot water demand of the house, period.

[dbuck50]

Not true for me on tankless providing enough hot water. We had never had an issue on running out of hot water yet. Not only between me and my wife, but with 4 others staying in the home and all showering at roughly the same time.

Anybody know what the rough percetage of fuel I would save running cold start and an indirect WH?

[johnsp]

Your savings would mostly be in the non-heating months. So I'd guess 5-10% of your total yearly bill. Now do you
burn 700 or 2000 gals a year? Are you in Alaska or Virginia with a 10 month winter or a 5 month winter?

If your boiler is oversized, you'll be wasting fuel all the time. I'd only put an indirect on a boiler replacement
or if there was a shortage of hot water. I don't see the payback in your situation. Might make more sense to lower the min temp of the aquastat to 120° and high limit to 140°
during the summer.