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Bosch Greenstart Combi 151 Tankless VS Traditional Burnham ES25 + Bradford White Gas Water Heater

TGI7 Member Posts: 1
edited February 2019 in Gas Heating
Thank you very much in advance for any input you can provide.

So we have a small-ish house (~1900 sq ft "Colonial", basically it was originally a ranch but they added a 2nd floor on top) with 3 full bathrooms (1 on 1st floor, 2 on 2nd floor) in the New York City Metro area. The house has 3 floors (Ground level, 2nd floor, and basement). Eventually we plan to add a 4th bathroom in the basement. Family of 4 with myself, wife, and 2 young boys under 5yrs old.

We currently have oil heating via a Peerless WBV-something (I'll get the actual model number) with a John Wood 50gal Booster tank with baseboard heating, both are quite old and we are told by our maintenance company that it is time to replace them. I'm worried about a random leak of the 50gal booster tank plus the fact that we have 2 young children leads us to want to replace the equipment sooner rather than later. So if we're going to spend the $$ may as well convert to gas. We already have gas lines ran to the boiler area since we use natural gas for laundry dryer + cooking + pool heater.

My wife is a stay-at-home mom and we keep the temp usually at 69 during the day (in winter) and 64 unoccupied. Living is by floor throughout the day so lets say:

1st Floor (Living Room, Kitchen, etc.):
Morning: 69
Nap-time: 64
Afternoon: 69
Evening/Bed-time: 64

2nd Floor (Bedrooms)
Morning: 64
Nap-time: 69
Afternoon: 64
Evening/Bed-time: 69

This may not be the most efficient way to heat things, and I heard with mod/con boilers, you should keep the temps relatively constant (within 2 deg variance) for maximum fuel savings.

I am not very handy at all, so called 6-7 companies for quotes. The company we decided to go with is proposing 2 options:

1) Bosch Greenstar FS 151 Tankless Floor-standing Mod/Con boiler exhausting via PVC pipe out the existing chimney (no need to change existing chimney liner). This unit does 4.0 GPM for hot water heater + general house heating in one unit.

2) Burnham ES25 "Traditional" gas boiler for heating + separate Bradford White 75gallon gas water heater

The initial cost is roughly the same (2nd, "Traditional option is $1,000 less). Since the project cost is no chump change, I would like to ask if anyone has had great or bad experiences with either brand? Or can suggest to go one way or another? (Or even suggest alternative brands/models)

Pros/Cons of each seem to be:

Bosch Tankless Combi PROS:
- Saves $$ on gas if tuned correctly (the installer suggests $500 - $600/yr savings based on our house and family make-up)
- Once hot water is flowing, supposedly way less chance to "run out" (say, if few people take long, consecutive showers)

Bosch Tankless Combi CONS:
- Requires more maintenance (every 2-3 years, have to run some cleaning solution through the heat exchanger)
- During power outages, both hot water + heating service will be unavailable
- Putting "all our eggs in one basket". If the single unit fails, we lose hot water + heating

Burnham + Bradford White PROS:
- The installer tells us basically no maintenance. But I'm thinking annual tune-up by service company.
- During power outage, we would likely still have hot water service
- Heating and hot water are separate systems, so one unit failing will not affect the other

Burnham + Bradford White PROS:
- Will burn more gas (the installer suggests gas costs will be an extra $500 - $600/yr based on our house and family make-up)
- Change for hot water to run out during intense usage sessions (though it may be hard to burn through 75 gallons in one shot?)

Based on the list above, and if I'm valuing low-maintenance and reliability, I am included to go with the "traditional" Burnham + Bradford White combo. However, as its 2019 now Its hard for me to justify installing "older-style" equipment, especially if I'm going to spend this much money.

I will provide more information such as measuring out the length of baseboards we have per floor (basic, slant-fin stuff). If there's anything else I can provide to help give recommendations, please let me know! Thank you very much, again, in advance.


  • Jamie Hall
    Jamie Hall Member Posts: 21,105
    Others will chime in. My comment is this: it is very rare for a tankless unit to be properly sized for the heating needs, if it is properly sized for the hot water needs -- and vice versa. Usually it is much too big for the heating needs. Did the contractor do a full heat loss calculation on the house to determine the actual heating needs? If not you really don't know -- and neither do they -- just how much heating boiler you actually need, and can't make an intelligent choice.

    I doubt very much whether there would be much difference in gas usage between the two units; the figure quoted for the difference seems way high to me.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • KC_Jones
    KC_Jones Member Posts: 5,409
    1900 sq ft of space being heated?

    I'd go with neither as they are both over sized.

    I also agree with Jamie a combi isn't great at either job it's being asked to do.

    What is the heat loss of the building? How much emitter capacity do you have? Those 2 things are very helpful in determining your path forward.

    A normal mod/con boiler will certainly save money through modulation, but there is also the condensing component. You need excess emitter in relation to the heat loss to take full advantage of that part. Though not a requirement, the installer should lay this out for you so you have proper expectations.

    Also keep in mind that savings they are quoting could, in part, be the difference in cost from oil to gas, around me there is a significant difference in the fuel cost. For "real" savings it's about how many BTU's or fuel units you will save.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15