Gas DHW Heater and Oil Boiler?

n75040

Hello all,

Novice homeowner here, who has purchased a new house and the previous owner before sale had replaced the DHW with a 75 gallon Bradford White natural gas hot water heater.

The house is also equipped with a Buderus g-215/4 oil boiler with the 3 zones, radiant heat in the kitchen and 1 bath, cast iron radiators throughout the rest of the house.

My plumber expressed some concern about the boiler not being used in the off-season since it is not used for DHW and might be subjected to condensate damage.

He was suggesting that I scrap the gas DHW (which is newly installed) and install DHW tank that works off of the oil boiler instead. He quoted me quite a hefty price for installation.

Is it feasible, if I'm not wanting to scrap the newly installed gas fired DHW to instead have someone install a new honeywell aquastat (L7224U?) that has a low limit setting, so I can set the low limit to I believe 105-115F and make sure the Buderus boiler won't be subject to condensate damage?

My plumber also expressed concern that both of the flue pipes for the gas dhw and oil boiler are going into the same chimney and could possibly be a violation. Is this something I need to be concerned about as well?

Hot_water_fan

Unfortunately, it is time to find a new plumber!

Jamie Hall

The combination of the gas hot water heater and oil boiler isn't a problem. However, I'm not really enthusiastic about both of them exhausting into the same flue. That may be a problem.

n75040

ok, so the buderus is built to be able to "cold start" (?) and I don't have to worry about it not maintaining a constant temperature of 105F during summer to protect itself from condensate damage?

The low limit aquastat seems fairly cheap ($200?) and would it use that much oil during the summer to maintain a low limit temperature (105F)? I wouldn't mind having it installed if it would greatly extend the life of the boiler.

STEVEusaPA

Show us a pic of what you got, far enough back to see both appliances and how they are hooked into the chimney.
I wouldn't try to maintain temp with the boiler. It would be a waste. If your gas-fired water heat took a dump, an indirect off the boiler isn't a bad idea.

n75040

Hot_water_fan

ok, so the buderus is built to be able to "cold start" (?) and I don't have to worry about it not maintaining a constant temperature of 105F during summer to protect itself from condensate damage?


The low limit aquastat seems fairly cheap ($200?) and would it use that much oil during the summer to maintain a low limit temperature (105F)? I wouldn't mind having it installed if it would greatly extend the life of the boiler.

Where exactly does the plumber think the condensate would be coming from? Exhaust gases can condense if return water temperatures are low enough (bad in your boiler's case, good in other boiler's cases) but you would need flue gases for that to be a problem and if the boiler is off for the summer...No flue gases.

ethicalpaul

The answer is the opposite of what he recommended. You should HOPE that oil burner rots out so you can replace it with a natural gas unit and stop paying $5/gallon and having a hazardous materials storage tank on your property

n75040

Well that was my other question, what's the feasibility of installing a new burner and converting to gas? I would need to have someone evaluate if the size of my gas line coming in is large enough? 

EBEBRATT-Ed

You could put a power gas burner in that boiler if Buderus allows it. Call them and find out.

I think your plumber is looking for work. Find a new one.

Steamhead

EBEBRATT-Ed said:

You could put a power gas burner in that boiler if Buderus allows it. Call them and find out.

I think your plumber is looking for work. Find a new one.

You can get Carlin and Riello gas burners specifically for these boilers.

bburd

n75040 said:

Well that was my other question, what's the feasibility of installing a new burner and converting to gas? I would need to have someone evaluate if the size of my gas line coming in is large enough? 

Yes, you would need to have the sizes of your gas pipes checked, as well as the adequacy of the meter. Any competent HVAC contractor who does gas work can do this.

HVACNUT

Buderus has their "thermostream" design for the G215 which mixes return water with the supply at the top of the boiler while the burner heats the block and 360° of water. That and they infuse elastic or something into the cast iron for flexibility which they claim makes the boiler virtually unshockable. (Is that a word?)
That being said, it looks like you have high water volume (large piping and CI radiators?) and IMO, primary/secondary piping couldn't hurt if used as a cold start. 
BTW, the optional control for that boiler is the Buderus R2107 Logamatic. And that control keeps the boiler off unless outdoor temperature says it needs to fire. So all summer it sleeps and sleeps.

HVACNUT

On an off topic side note. Anyone else notice the "Thank" thingee is a 👎?
@Erin Holohan Haskell?

EdTheHeaterMan

If you ever saw the show "The Music Man", Then you know what kind of plumber you have. Prof. Harold Hill is the plumber. You are the town of River City, a new Boiler is the "Boy's Band," and now there are several @unethicalPaul types that will add to your worry about two different fuel sources (gas and oil heat exhaust) venting into the same chimney. When many of these naysayers are aware of duel fuel burners that can operate on both OIL and GAS, by just flipping a switch. That switch does not change the flue to a different chimney @Jamie Hall as far as I know. but I could be mistaken, so let me read these instructions.
I see nothing about swapping to a different chimney here?!?

The venting of a gas water heater into the same masonry chimney as the "cold start" oil boiler is a common thing. As long as the gas vented appliance vent connector enters the chimney above the oil appliance vent connector.

The concept is that oil heat appliances seem to accumulate more solid deposits at the bottom of a masonry chimney, if allowed to build up over time, the vent becomes blocked. This usually ends up in an horrible odor and soot deposits inside the boiler room. The home owner then calls for service to find that lack of maintenance has caused the boiler to become partially plugged and extra time is needed to clean the heat exchanger and the base of the chimney. No one gets sick or dies from carbon monoxide poisoning.

If however the gas appliance was to vent lower that the oil appliance the debris from the oil appliance could block the gas vent without any one knowing about it until a sever case of CO poisoning occurs. This is because the gas appliance would vent CO into the home with less chance of detection. This was all allowed by the code with pressure from the natural gas utilities as a marketing ploy. They wanted to get oil heat customers and coal heat customers to agree to place a gas line into their home and an automatic water heater was a very inexpensive "First Appliance" as long as it could be vented in the existing chimney.

Once the gas line was in the home, the choice to switch to Gas heat was much easier for the homeowner.

As far as the gas appliance that is venting into your chimney... It is installed correctly/. Your job is to have a professional oil heat technician do the proper maintenance every year on your oil burner, and it MUST include inspection of the chimney base and cleaning if needed.

You don't live in River City and you don't need a Boy's Band. What you need a different plumber.

EdTheHeaterMan

n75040 said:

ok, so the buderus is built to be able to "cold start" (?) and I don't have to worry about it not maintaining a constant temperature of 105F during summer to protect itself from condensate damage?

The low limit aquastat seems fairly cheap ($200?) and would it use that much oil during the summer to maintain a low limit temperature (105F)? I wouldn't mind having it installed if it would greatly extend the life of the boiler.

Cold start means that the boiler does not maintain a minimum temperature. Some boilers have a tankless coil inside the cast iron boiler for domestic hot water. You have a separate water heater, you have no tankless coil so, no need for you to maintain temperature in the Buderus Boiler, That thing is a tank and will last many, many years as a cold start boiler. It is just a waste of fuel to maintain temperature higher than the boiler room temperature.

Competent professional maintenance is all you need.

Erin Holohan Haskell

HVACNUT said:

On an off topic side note. Anyone else notice the "Thank" thingee is a 👎?
@Erin Holohan Haskell?

Good catch! This was a reaction that we customized, but it got overridden by a recent update. We'll investigate. Thanks!

Larry Weingarten

Hi, There seems to be some confusion about whether or not you can use one vent for oil and gas appliances, but this discussion might help. https://forum.nachi.org/t/oil-and-gas-venting/8365

Yours, Larry