Looking for the smallest BTU input condensing gas boiler

bob eck

What manufacture has the smallest BTU input gas condensing boiler?
Burnham, Lochinvar, Weil Mclain, HTP, peerlees, Navien, Bosch, Rinnai, ICB, NIT or any other condensing heating boiler only.
What is the turn down on the condensing boiler with smallest BTU input?

HardBoiled

RInnai E50cr is a combi with a heating input range of 13.6 - 50 mbh. Has a 85 mbh top end on DHW. Heating TDR is 3.7 : 1

Not sure if there are any other combis that small, but there are some small heat only models:
RInnai E60sr: 60 mbh
Bosch: 57 mbh
IBC: 51 mbh
HTP (EFT): 55 mbh
Laars: 50 mbh
Lochinvaar: 55 mbh
Navien: 55 mbh
Utica/Dunkirk: 50 mbh
Peerless: 50 mbh

Energy Star has a good residential gas condensing boilers page:
https://www.energystar.gov/products/most_efficient/boilers

NY_Rob

Last time I checked, the lowest modulated output was 8K BTU's.

The HTP UFT-80W with 10:1 turndown gives you up to 80K BTU's for for fast DHW indirect tank heating and down to 8K BTU's for spaceheating.
You can also limit it's fire rate between 100% down to 50% (on both spaceheating and DHW supply) so it can be a 40K BTU output boiler for spaceheating and an 80K BTU boiler for DHW.

rbeck

The USBoiler (Burnham) has two the K2WT80 (watertube) and the Aspen ASP85 (firetube) both are 10:1 turndown. So minimum is 8K and 8.5K respectively. The inputs can be reduced for heat or hot water independently.

Rich_49

bob eck said:

What manufacture has the smallest BTU input gas condensing boiler?
Burnham, Lochinvar, Weil Mclain, HTP, peerlees, Navien, Bosch, Rinnai, ICB, NIT or any other condensing heating boiler only.
What is the turn down on the condensing boiler with smallest BTU input?

Should be asking what units have the lowest output .

SuperJ

It seems to me that if your are running primary and secondary loops with a constant primary flow, you would get better efficiency with a buffer tank, than a high TDR boiler (even with a nice low min fire rate). Since at low loads your primary loop is basically going around in a circle resulting in a hot return temperatures.
Some boilers (like Lochinvar) have a 0-10v output for a variable speed primary pump that should give you some efficiency from less diluted RWTs.
I’ve noticed the smaller modcons seem to have lower TDRs, almost as if they were just throttled versions of their higher output siblings.

tim smith

Lochinvar whn056 has a 10:1 turndown, 8.3 thousand btu low fire.

Brewbeer

SuperJ said:

Some boilers (like Lochinvar) have a 0-10v output for a variable speed primary pump that should give you some efficiency from less diluted RWTs.

What small pumps currently available have a 0-10v input for speed control?

SuperJ

I’ve seen a couple. I’ve seen a Grundfos UP style pump with a 0-10v. I think it had a VS designation. Was before ECMs got popular.

I know either Taco or B&G offers it on a small ECM circ. but you have to buy an add on for the pump.

EDIT. Here is a thread that covers the topic.
https://forum.heatinghelp.com/discussion/163190/0-10v-circulator-pump

1sttimeposter

SuperJ said:

It seems to me that if your are running primary and secondary loops with a constant primary flow, you would get better efficiency with a buffer tank, than a high TDR boiler (even with a nice low min fire rate). Since at low loads your primary loop is basically going around in a circle resulting in a hot return temperatures.

Some boilers (like Lochinvar) have a 0-10v output for a variable speed primary pump that should give you some efficiency from less diluted RWTs.

I’ve noticed the smaller modcons seem to have lower TDRs, almost as if they were just throttled versions of their higher output siblings.

This's very interesting. We just installed an IBC SL10-85 G3 and have an Alpha2 pump on the primary heating loop.

I don't think this Alpha2 is hooked up to the 0-10v output terminal on this IBC which has, but curious how a variable speed pump hooked up to a 0-10v output can help efficiency from less diluted return water temp.

Thanks in advance.

Zman

Condensing boilers are more efficient when return water temps are low. With the boiler managing the circulator, it can slow the flow during low fire to increase the boiler delta t and maximize efficiency.

Voyager

I don’t think it is the lowest output, but I have been pretty happy with my Triangle Tube CC50s thus far. It was fairly cost effective to buy and it has a DOE output rating of 46 and I think it has about a 4:1 turndown capability so minimum output is probably 12 or so. My building has a design temp heat loss of 38, and the little TT is working well so far.

My typical SWT is upper 70s low 80s with RWT in the low 60s.