IBC capacity

ryanwc

My HVAC company, which has been doing service for a few years, suggests I replace my 14-year old Peerless Purefire 140 with an IBC CX 199. He calculated my heat loss at 97K. He is suggesting that we use the new one for hot water as well.

Am I right to think a 150 might work? Sure, a hot water heater can run 30-40K btu, but we wouldn't normally have it on all day.

He also says that this boiler will condense no matter what the water temperature, so that it would be condensing even when pumping out 170-degree water for our fin tube zone 2, as well as 140-degree water for our cast iron zone 1. Is that accurate? I thought you needed to be at lower water temps to condense.

I should note that we've never really come close to the capacity of our existing 140 btu unit, another reason why I'm not sure adding DHW would need to push us past the 150 unit.

GGross

Is the installer proposing an indirect water heater tank? or is this a combi boiler? for a combi 199 is probably needed for the flow rates, if it is an indirect tank, then you do not need a 199, in that case yes you are right a 150, or possibly less would work just fine.

The contractor is incorrect about condensing at every temperature. They likely have received poor training on the unit, from what I gather the IBC combi boilers are capable of producing DHW while using condensing boiler temperatures which could have been misunderstood by your contractor (this was information I received from a local rep and I have not confirmed it for myself but our local is trustworthy).

The boiler will not be condensing if running at a steady state of 170, but if you heat the house with 170 supplied on the coldest day, then that means you can have it lower for the rest of the year and will most likely still condense quite a bit.

ryanwc

Thanks. That's very helpful. He is proposing a combi, so maybe the larger model is needed.

And it's interesting that it can condense at DHW temps. He had said it could condense no matter what water temp and said that there was some sort of secondary heat exchanger (I think, but he may not have said heat exchanger. It may have been something else).

I'm hearing that you're skeptical of "no matter what temp", but that maybe there is mechanism that is somehow helping it condense even at higher temps than what would have been considered normal.

A second company is coming out today to give me another opinion.

GGross

I would highly recommend asking one of your contractors about a boiler with an indirect water heater (tank) in my opinion having a tank is much better than a tankless, but that decision is more of a personal one.

ryanwc

Second opinion — need to replace valve. Boiler is fine. Water heater is fine. No replacement called for at all. 

 I even pressed him, without saying a different contractor said the system is on its last legs. But gave him several openings to upsell me if he thought there was any reason. Nope.  “It could die anytime, but I don’t see any particular reason to think it will.”

Hmm. 

ryanwc

Why do you recommend an indirect tank?  

Teemok

Indirects hold heated water so you can draw it to the faucet faster. Flat plate heat exchangers in combi's need regular maintenance descaling depending on use volume and water quality. The combi will take a bit longer to get stable output and has lower max flow rate. Temperature rise declines as flow increases. They take up less space and don't leak like some tanks do but they can leak at connections with plastic parts. You won't fill a large tub as fast with very hot water with a combi. Indirects are easier to troubleshoot and most of the time fix with universal parts. The standby efficiency difference isn't really significant, becoming bigger with long periods of no use.

hot_rod

It really comes down to how much hot water ypu use or need. A 150 combi would get you around 3 gpm continuously. Or be plenty of power to run a separate indirect. If the 140 covered the load, a 150 surely would.

Pros/ cons. Wait time for hot with a combi, some maintenance required. Pros, endless dhw, no standby loss

Indirect, Pro: big dump load at any gpm for fast filling tub, quick delivery, multiple faucets can run together.
Cons, cost, size, more piping required, a small heat loss from tank.

Check water quality spec, see how your water will treat the tank Chloride level is important in stainless indirects.