Boiler and indirect questions

[Pulse]

1) Fire tube vs Water tube? Any notable advantages of one over the other?
2) If my boiler had 79k BTU output instead of the ~49k(estimated I need), is it fine to run a boiler at low fire using its turndown 24/7?
3) If my boiler BTU output is 49-79k BTUs and I am running at 120 degrees will an indirect hot water tank still work efficiently? It seems most 40-50gal tanks want 90-100k BTUs and only show ratings when the boiler is run @ 180 degrees
4) The only way to get mid 90s efficiency is to have the return water of the boiler ~100 degrees right?

5) Below is a list of boiler manufactures that I have researched. What do you guys suggest and is there someone I should add/remove to/from my list?
Brand(model) - Parts warranty - Heat exchange warranty - Prices

• IBC(SL series) - 5yrs -10yrs then prorated lifetime - ~$3.2k (so far my top pick)
• Lochinvar(Knight) - 5yrs - 10yrs the prorated till 15yrs - $3.4-3.8k (2nd pick)
• Navien(NHB) - 5yrs - 15yrs - ~2k(NHB) - (would be one of my top picks but is completely unavailable in my area)
• Rinnai(I-series) - 5yrs - 12yrs - $2.5-2.7k
• Bosch(greenstar) - 5yrs - 10yrs then prorated lifetime - $2.2k-2.4k
• Lennox(GWM) - 10yrs - 15yrs - ~6-7k(double anything else, WTF??) (surprisingly the best warranty)
• Weil-Mclain(evergreen) - 5yrs - 12yrs - $2.8-3.6k(evergreen)
• HTP(UFT/Elite Ultra/FT) - 5yrs - 10/12yrs - no prices yet
  
• Utica(SSC/SSV) - 2yrs - 10yrs then prorated till 15yrs - no prices yet
• Slantfin(CHS) - 5yrs, 10yrs then prorated till 15yrs - no prices yet
• Viessmann(Vitodens) - 5yrs -10yrs then prorated lifetime - $3.7k (Most likely not in my area)
  
• Triangle Tube(Prestige) - 2-6yrs - 10yrs - ~$3.1k

Thank you!

 

[Sylvan]

Burnham , Weil-Mclain and Slant fin, HB Smith , Crown Aruba .Utica are all the brands I installed and not a single call back .

 

[Sponsor]

 

[Pulse]

Burnham , Weil-Mclain and Slant fin, HB Smith , Crown Aruba .Utica are all the brands I installed and not a single call back .

I eliminated US boiler(burnham) because they only have a non-prorated warranty on their HE for 7yrs. I removed anyone without at least 10. I have the others on the list, but not Smith or Crown, after looking them up they seem to be focused more on commercial/cast iron.

 

[Dana]

1) Fire tube vs Water tube? Any notable advantages of one over the other?

The comparatively low pumping head of fire tube boilers make them a bit more flexible and system-design forgiving. In many/most residential applications it's possible to pump-direct (no primary/secondary) with a fire tube boiler, only rarely with water tube boilers.

Whenever primary/secondary is necessary the water going out to the radiation is a few degrees cooler (since it's mixed with cooler return water ) and the entering water temp at the boiler is a few degrees warmer (since it's mixed with boiler output), reducing the raw combustion efficiency. That makes it easier to tweak the last couple percent efficiency out of a fire-tube boiler than with a water tube boiler.

2) If my boiler had 79k BTU output instead of the ~49k(estimated I need), is it fine to run a boiler at low fire using its turndown 24/7?

Yes. With a modulating condensing boiler the "Holy Grail" is to size it correctly and tune the outdoor reset curve to where it burns nearly continuously at the lowest (=most efficient) water temperature that still keeps up with the heat load. The lower the minimum-fire output, the fewer the total number of ignition cycles per season.

3) If my boiler BTU output is 49-79k BTUs and I am running at 120 degrees will an indirect hot water tank still work efficiently? It seems most 40-50gal tanks want 90-100k BTUs and only show ratings when the boiler is run @ 180 degrees

When set up for an indirect most boilers have hooks for setting it to a higher burn rate (upt the maximum firing rate & temperature) for serving the indirect, even if the reset curve is calling for 100F water on a mild day.

4) The only way to get mid 90s efficiency is to have the return water ~100 degrees right?

Rong.

Efficiency is both a function of entering water temperature and the modulated firing rate. For most condensing boilers an entering water temp of 115F at a firing rate somewhere in the lower third of it's range would deliver mid-90s efficiency. It might take 100F EWT (or lower) to hit the mid-90s efficiency at max fire though:

As a rule of thumb for natural gas burners I use 120F AWT (125F out, 120F return) as the mid-90s threshold.

5) Below is a list of boiler manufactures that I have researched. What do you guys suggest and is there someone I should add to my list?

HTP's UFT series are relatively inexpensive but pretty robust fire tube boilers with a 10:1 turn down that come pre-plumbed with a secondary port for supporting an indirect water heater. It's even advertised as "No Primary-Secondary Needed".

The smallest of the line is the UFT-080W, which is enough boiler for 19 out of 20 houses in the US, runs less than $2K through distributors, sometimes under $1700. The min-fire output at condensing temps is ~7600 BTU/hr, but it'll still put out a solid 70,000 BTU/hr+ at non-condensing temperatures. If you have a load of 49K or less, that's your boiler. It's very comparable to the Lochinvar WHB/KHB 085, but with somewhat fewer bells & whistles to program.

The identical boilers are also sold under the Westinghouse nameplate as the WBRUNG series. The sales & warranty channels are the only difference. The Westinghouse tech support line rings in HTPs headquarters in Massachusetts.

That series was designed and manufactured by a first-tier Korean boiler manufacturer, Kiturami, that successfully competes head-to-head with KD Navien in the home country. But they have taken an OEM approach to the North American market, whereas Navien set up their own distribution and support channels here. Kiturami also sells similar fire tube boilers (albeit with less of a turn down ratio and no port for the indirect) through Laars, and they sell tankless water heaters (water tube type) and combi-boilers to a number of US tankless water heater companies.

Before picking a boiler, run the napkin math on the zone radiation- the minimum firing rate is more important than the maximum firing rate.

 

[Pulse]

First off, thank you for all this info!

When set up for an indirect most boilers have hooks for setting it to a higher burn rate (upt the maximum firing rate & temperature) for serving the indirect, even if the reset curve is calling for 100F water on a mild day.

Makes sense, but how does this fair efficiency wise? ..especially in the summer months with the boiler only running at a high temp for the indirect hot water.

Yearly cost of a indirect vs a 199K BTU tankless(~$200)? 199K is needed to achieve at least 5 GPM in my area.

Efficiency is both a function of entering water temperature and the modulated firing rate. For most condensing boilers an entering water temp of 115F at a firing rate somewhere in the lower third of it's range would deliver mid-90s efficiency. It might take 100F EWT (or lower) to hit the mid-90s efficiency at max fire though:

Since I only want a boiler to function at a fraction of its potential, I should maybe shoot for a little more boiler BTU output as long as the turndown/minimum BTU works for my setup. So far I have been looking at ~80k BTU boilers because not all companies have ~50k BTU boilers. If I increase that range to the next level ~110-115k boilers I may be better off?

Before picking a boiler, run the napkin math on the zone radiation- the minimum firing rate is more important than the maximum firing rate.

Minimum fire rate for 80-115k boilers seems to be in the 8-14k range. As long as one of my zones is demanding BTUs in that range, I am golden?

 

[Dana]

Makes sense, but how does this fair efficiency wise? ..especially in the summer months with the boiler only running at a high temp for the indirect hot water.

The efficiency of a mod-con running an indirect as it's only load is only slightly below that of a condensing tankless. A lot depends on the total volume of hot water used, and the quality of the installation. (I can't believe how many installers don't bother to insulate the pipes!) The thermal mass of most mod-con boilers is pretty small compared to cast iron boilers, so the amount of heat abandoned in the boiler is pretty small. Most can be set up to post-purge heat out of the boiler's heat exchanger into the the water heater, bringing the temperature of the remaining water in the boiler down to near whatever the indirect's storage temperature is set to.

The raw combustion efficiency of a mod-con at 180F and max-fire is about 86-88%. That's still way better than a standalone atmospheric drafted tank type water heater (78-80%), and the standby losses of indirects are lower than standalone tank heaters,since without clearances for burners to worry about they are more fully insulated.

The temperature it serves to the indirect is usually programmable, but it's a good idea to set the tank and the boiler at temperatures at which deliver most or all of the max-fire output of the boiler, to keep the recovery times short when giving the tank priority.


Since I only want a boiler to function at a fraction of its potential, I should maybe shoot for a little more boiler BTU output as long as the turndown/minimum BTU works for my setup. So far I have been looking at ~80k BTU boilers because not all companies have ~50k BTU boilers. If I increase that range to the next level ~110-115k boilers I may be better off?

Size the tank for the domestic hot water load. Upsizing the boiler us usually the wrong way to go, with only a few exceptions. For a simple 4 person family and no gia-normous spa to fill a 50-80K condensing boiler is fine. There is no point to up-sizing it to 100K+.

When looking at the turn-down ratios bear in mind the output of the radiation at condensing temperatures. Fin tube baseboard might be good for 500 BTU/hr per foot at an entering water temp of 180F, but it's only good for about 200 BTU/hr per foot at an entering water temp of 125F, which is where it needs to be to hit mid-90s efficiency. An 8K-in/7.6K out minimum firing rate still needs about 7600/200= 38' of typical fin-tube baseboard to not cycle at all on that zone. That same 38' of zone radiation can deliver 19,000 BTU/hr or so with 180F out of the boiler.

 

[Pulse]

When looking at the turn-down ratios bear in mind the output of the radiation at condensing temperatures. Fin tube baseboard might be good for 500 BTU/hr per foot at an entering water temp of 180F, but it's only good for about 200 BTU/hr per foot at an entering water temp of 125F, which is where it needs to be to hit mid-90s efficiency. An 8K-in/7.6K out minimum firing rate still needs about 7600/200= 38' of typical fin-tube baseboard to not cycle at all on that zone. That same 38' of zone radiation can deliver 19,000 BTU/hr or so with 180F out of the boiler.

I was thinking about doing panel radiators instead of baseboard. I know panel rads are a slower heat, but they provide convection and radiant heat. I also did not want baseboard on every single wall.

I actually drew my house in CAD, take a look:
-removed-

https://www.ecomfort.com/stories/1238-Radiator-Sizing-Calculator.html

I was using the above calculator to find out what I needed in my largest zone(living/dining/kitchen/hall/entry foyer). ~1000sqft
It claims roughly 18k BTUs are needed.

So, I had plans to have 3-4 16"x72" panel rads(~3500 BTUea @ 120), which would be 10.5-14k BTUs, in addition to a couple smaller ones.

That zone should never cause short cycles in the boiler even if the basement zone, and 5 bedroom zones are not on. In that setup I have 6 zones:
Zone 1) living/dining/kitchen/hall/entry foyer
Zone 2) Basement
Zone 3-6) Bedrooms

OR, I could do just 3 zones:
Zone 1) living/dining/kitchen/hall/entry foyer/basement
Zone 2) 2 bedrooms in new addition
Zone 3) 3 bedrooms in old house

 

[Dana]

Panel rads are not "slower heat" than baseboard of equal output. The converse is true- both the room temperature and comfort levels come on faster with panel rads (comfort preceding temperature due to the radiated output.)

That ecoComfort radiator sizing tool is a piece of junk. Before buying anything, run a real Manual-J room by room, or cook up an IBR load calc in a spreadsheet based on the actual construction U-factors & window U-factors.

A sorta-man-J online freebie that isn't terrible for most construction is loadcalc, but it regularly oversizes by 25-30% or more even with fairly aggressive assumptions on the inputs (subtract out the infiltration & ventilation loss numbers and it's closer), and it doesn't let you fine-tune things. An ACCA approved cheap/free Manual-J tool is CoolCalc, but like any other tools, it can lead one astray if you don't take the time to really figure out how to use it properly.

Keep it to 3 zones if you can. Micro-zoning by bedroom almost never works well on a low mass system. Even fairly lossy bedrooms have design heat loads well below the minimum modulated output of a mod-con, and the average load during the season is only a fraction of that. Running the three bedrooms as a single zone, and putting TRVs on panel rads to tweak the room-to-room temperature balance can work.

In my own home I was pretty much forced to micro-zone due to wildly different heat loss characteristics of various rooms, and ended up installing cast iron rads in the bedrooms feeding from a 125F -130F central buffer tank to keep the ~17K minimum-output burner from short cycling. Newer boilers can go much lower than that- I could probably have done it with TRVs running three bedrooms as a single zone if starting from scratch today and saved the cost of the buffer.

 

[Pulse]

@Dana
Thanks for all that info, now I am on step 2, piping..

Series?: https://imgur.com/a/Wk0lnWI
Two pipe reverse/direct?: https://imgur.com/a/rI6IJJ0
Homerun: https://imgur.com/a/BLQP9ho

What is the best way for me to pipe my system

 

[Dana]

Are you going to be using TRVs?

Clearly a home-run system is going to be the most flexible for tweaking in room-to-room temperature balance issues, but it's also a lot of pipe.

Doing it with separate pumps for each zone rather than a single ECM drive smart pump and zone valves is often a recipe for over-pumping. The pumping head of panel rads is pretty low, and you don't usually need more than ~1 gpm through a given rad.

 

[Pulse]

Are you going to be using TRVs?

Clearly a home-run system is going to be the most flexible for tweaking in room-to-room temperature balance issues, but it's also a lot of pipe.

Doing it with separate pumps for each zone rather than a single ECM drive smart pump and zone valves is often a recipe for over-pumping. The pumping head of panel rads is pretty low, and you don't usually need more than ~1 gpm through a given rad.

TRVs will only be in the bedrooms, I don't know why I would want individual control over a rad in living/kitchen/basement. If I have 3 zones, where is my thermostat for each zone typically located?

Yes, a homerun will be A LOT of 1/2 pex, what would be the next best piping system? From what I have seen these are the options:
Two pipe direct/reverse, one pipe, series loop, and homerun

I can switch to a single pump with zone valves. I did not know which one would be best for me. If a run is a certain length is there a time when you want individual pumps?

 

[Dana]

With a home run you can usually back off to 3/8" PEX and still get reasonable flow.

To figure out the pumps requires calculating the pumping head on each zone/loop (which can get complicated) at 1 gpm, 2gpm and 4gpm. Ideally you'd always be under 2gpm, which limits noise and pipe erosion, and delivers an adequate delta-T but not too large a delta-T. Smart pumps can be set up for constant-pressure or constant flow, or delta-T, but it still has to have an adequate range to work with.

 

[Pulse]

With a home run you can usually back off to 3/8" PEX and still get reasonable flow.

To figure out the pumps requires calculating the pumping head on each zone/loop (which can get complicated) at 1 gpm, 2gpm and 4gpm. Ideally you'd always be under 2gpm, which limits noise and pipe erosion, and delivers an adequate delta-T but not too large a delta-T. Smart pumps can be set up for constant-pressure or constant flow, or delta-T, but it still has to have an adequate range to work with.

I have a lot of research to do on pump/pipe size, but as for the method of piping used, the below list is basically what I choose from right?
Two pipe direct/reverse, one pipe, series loop, and homerun