Analyzing and deciding between bids - Propane combi boiler in Vermont

Kate111

We currently have a 30 yr old propane boiler with 4 zones. One zone is for indirect DHW for which we have a storage tank. This system has worked well for us. We got bids from 2 local outfits - one our propane dealer who also sells, installs, services boilers, the other is our HVAC / plumber. Reputation-wise, we are comfortable with either. Propane dealer recommends going tankless for DHW, and installing a Rinnai combi boiler. HVAC guy recommends keeping our indirect DHW storage tank and installing a NTI FTV combi boiler, using one zone for DHW as we have now. Our water quality is excellent except for being somewhat acidic. We have a water quality system installed to bring the pH back to neutral. Major differences between the quotes - the Rinnai has slightly better warranty (12 yrs, not 10) on heat exchanger, one recommends installing new high-efficiency circulating pumps and one doesn't. Would appreciate some expert thoughts and opinions. Thanks in advance. Kate

EzzyT

The NTI FTV isn’t a combi unit it’s just a boiler which would work great with your indirect tank.
Be sure that the boiler is plumbed primary/secondary piping schematic which is shown in the manual.
The high efficient circulators will pay for themselves relatively in a year or two. Most likely for the heating side of the system you could can get away with a single circulator and zone valves.

hot_rod

Do you have a tank style indirect? Is it 30 years old also?
How many people in your household?
Combis can work well for small families.
A heat load calc is a good first step.

GroundUp

EzzyT said:

The high efficient circulators will pay for themselves relatively in a year or two.

A year or two? Maybe if you're paying 2 dollars per kWh.... At 50 watts of savings, with the circ running 24/7, and a rate of $.10/kWh is $3.60/mo saved. Call it a 6 month heating season, and be more realistic with run time, we're talking less than $10 a year. By the time the payback is reached, you're about due for a new circ again.

EdTheHeaterMan

GroundUp said:

EzzyT said:

The high efficient circulators will pay for themselves relatively in a year or two.

A year or two? Maybe if you're paying 2 dollars per kWh.... At 50 watts of savings, with the circ running 24/7, and a rate of $.10/kWh is $3.60/mo saved. Call it a 6 month heating season, and be more realistic with run time, we're talking less than $10 a year. By the time the payback is reached, you're about due for a new circ again.

He is not looking at the big picture. The savings on electricity is only a portion of the circulator's cost of ownership. By using one circ and zone valves, you can get better comfort control with the proper pump setting.
This will reduce the gas bill a little too. Not big savings, but every penny helps.

On the other hand. I like to keep things simple. old school pumps are also just fine.

That said, I like the indirect tank over the tankless for the same reason. Too much junk inside a small box with the ModCon boilers, add a tankless water heater to the box and you are asking for a no heat or no hot water service call in the next 5 years that may be a several day affair.

Just my experience with Combi systems. Parts are not always on the shelf at the supplier.

EdTheHeaterMan

To clarify the zone valve idea. The DHW tank should have a pump, the Boiler should have a pump, and the system should have a pump Three pumps total. the system pump will operate whenever any zone valve is open on a call for heat from that zone. The ECM pump will work well for the system circulator.

That configuration is in the install instructions.

Alan (California Radiant) Forbes

You said the propane dealer recommended an on-demand for the DHW and a combi boiler? You don’t need a combi (heating & DHW) if you get a tankless. If you get a tankless, your boiler will be heating only.

Both suggestions sound fine. The benefit with an on-demand with a separate boiler is that they are independent. If one busts, the other one can make life bearable until the other one gets fixed. Also, with an on-demand, you’ll never run out of hot water.

I’d ask for references; even go visit one of their installations. It should look clean and neat with all the pipes insulated.