Triangle Tube or Cast Iron?

Users who are viewing this thread

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Ok, at last, we have a gas bill. The February number from degreedays.net for our weather station is 1306, and according to the gas bill, we used 414.49 therms that month (BTU factor is 1.028). The house was unoccupied most of that time and set to somewhere in the 68-70 degree range (I kept it warm to get a realistic gas bill). One hiccup: some workmen turned off the heat one day and forgot to turn it back on, and we had a frozen/burst pipe, so for about 12 hours the heat was off entirely and for about 12 hours it was cranked to maximum. The boiler is 160/128. Do I have all the info I need to make a calculation?

So, 128/160= 80% steady-state efficiency. If they billed in therms and not CCF there's no need to convert fo the BTU factor. 0.8 x 414.49= 332 therms of heat delivered into the heating system plumbing over 1306 HDD. That's 332/1306= .254 therms/HDD, or 25,400BTU/HDD.

In a 24 hour day thats 25,400/24= 1058 BTU/degree=hour.

Assuming an outside design temp of 0F and a balance point base temp of +65F (the HDD base presumption) that's 65F heating degrees...

...which implies a design heat load of 65F x 1058 BTU/F-hr= 68,770 BTU/hr.

For a 2500' house that's 27.5 BTU/hr per square foot of conditioned space, which is on the high side for a house that size.

An uninsulated but heated basement is probably worth on the order of 15,000BTU/hr, (give or take 5000 BTU/hr depending on the particulars)- insulating the walls to R10 would reduce that to 1,500-2000BTU/hr, so knock at least 12K off that 69K number and you're at 57K (probably lower) bringing the BTU/ft down to 23, but that's still a pretty high number for a 2500' house, which implies you may have gaps in the insulation elsewhere &/or high air infiltration rates.

The 57K is just barely over the DOE output of a Solo 60, the house was not being occupied, AND the boiler is probably not delivering 80% efficiency after 50 years of service. If we use 75% (which is still a bit optimistic) that 69K number is reduces to 69K x 75/80= 64.5K, and if you whack 12K off that number for insulating the basement you're at 52.5K, which IS within the output of the Solo 60. If there are going to be a couple of live humans there sleeping cut that to 52K, and with typical 24/7 plug loads you'd knock off another 0.5-1K from there, but even 50K is a pretty high number for a 2500' house with an insulated foundation- you either have a very unusual house shape or a lot of heat leaks.

A full Manual-J would be useful for estimating where those leaks might be, but it might be worth doing a blower-door & infra-red imaging assessment to spot & rectify the most egregious leaks even before insulating the basement. Electrical or plumbing or flue chases that run from the basement to the attic can move HUGE amounts of air into & out of the house even without the house feeling super-drafty. The flue of the atmospheric drafted antique boiler can itself impart a significant heat load from depressurizing the basement, drawing in air even when the burners aren't firing. Blower doors & IR imaging can find even the less-obvious thermal bypass culprits.

Then there's the issue that they only estimated the meter reading, more often than not with a thumb in the scale favoring THEM....

The manual-J came in at 51K even with the extra 5K+ of window losses due to ignoring the actual U-factor of your windows (11,610 BTU/hr x 0.30/0.57= 6111 BTU/hr, which is which puts it at ~45K. The Manual-J also accounted for 2987' of conditioned space, not 2500'. That's a ratio of ~45,000/~3000'= 15 BTU/hr per square foot of space, which IS in the credible range, but probably also on the high side of reality, depending on where else he might have underestimated the envelope performance.
 
Last edited:

Estrada

New Member
Messages
25
Reaction score
0
Points
1
Location
Illinois
"high air infiltration rates"

So, guess what? I totally forgot that we replaced every window, which means that for two days in February, which is the month we're looking at (and which was one of our coldest on record), the house had no windows at all. Yes, I am a genius, why do you ask?

I'll be back when I have a March bill. I'm also considering just going with a new cast iron boiler (and indirect tank), since by my math it'll take 13 years for a mod/con to pay for itself. But one thing I noticed is that Burnham, for example, sells plenty of smaller boilers, but their indirect tanks specify that the paired boiler output needs to be ~100k and up.
 
Last edited:

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
I suspect the "windows are free, glass costs extra" condition will indeed skew the numbers quite a bit! :)

An indirect tank only needs a bigger boiler if it needs to meet the gallons per hour specified in the documentation. The 3-plate mid-efficiency Burnhams (ES2-3, ESC3, etc.) put out about 60,000 BTU/hr, which is ~2x the output of a standalone gas hot water heater. As long as the zone controller gives priority to calls from the indirect, inhibiting the calls from other zones until the indirect's call for heat is satisfied, you'll have good to excellent hot water performance. Zone controllers with a programmable "priority zone" option are pretty standard fare these days.
 
Messages
64
Reaction score
0
Points
6
Location
Stonewall Colorado
I like the ESC3 option. Cheaper, more reliable, & longer expected life than TT Solo.

Myself & many others have had problems with TT Solo, Fail to fire lockouts, foghorn noise when modulating, gas valve replacements, etc. etc.

I'm putting a Burnham ESC6 (high altitude version) in my sons new build 4,000 ft2 house in Crested Butte Colorado.
 
Last edited:

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
At the ESC6's DOE output of 130K (before derating for altitude) that's 33 BTU/hr per square foot of conditioned space, call it 30BTU/hr-ft^2 after derating, which seems really high, even assuming your outside design temp is -15F. (Leadville's 99% outside design temp is -14F, and more than 1000' higher than Crested Butte.)

I'd expect the true heat load to come in under 80,000 BTU/hr for an older house, under 60,000 BTU/hr if it's tight & code-min new construction, which means the ESC6 is probably getting on to 2x oversized or higher. Did you run a Manual-J on that?
 
Messages
64
Reaction score
0
Points
6
Location
Stonewall Colorado
My son & builder & architect are not through with design yet. Lots of glass on Great Room / kitchen.
Crested Butte is about 9,000' altitude & design temp = -19*F Climate Zone 7.
Burnham says to derate 2% / 1,000' above sea level so 18%
Boiler room is in unheated garage, so I'm leaning toward using IBR output.

Probably the ESC5 will do, don't know yet.
 
Last edited:

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Placing a hydronic boiler outside the building's thermal envelope is a generally bad idea in a location with a -19F outside design temp.

With direct-vented equipment you don't need the air-leaky garage for combustion air. It doesn't take a whole lot of material to build a insulated partition wall between the boiler room & garage, eliminating the insulation in the section of wall between the boiler room & fully conditioned space. If access to the boiler room is only from the garage side, use an insulated exterior door for the access (even a cheap U0.25/R5 blank steel door will do- it doesn't need to be a thing of beauty.) That way the standby & distribution losses accrue predominantly to the conditioned space, rather than raising the temp in the garage 2-5F
 
Messages
64
Reaction score
0
Points
6
Location
Stonewall Colorado
Thanks, At about $275 / ft2 inside house is my Son's rational for garage boiler room, as you say it will be easy to insulate the stud wall & let heat go up to the floor of the conditioned space above.
 

Estrada

New Member
Messages
25
Reaction score
0
Points
1
Location
Illinois
Just to wrap up my story, our hot water heater started to leak, so without waiting for the March readings, I went with the Burnham Series 3 303 model with 70k input, and a Triangle Tube Smart 50 indirect tank. That seemed like the best compromise on size/cost/reliability. So the answer to my original question turned out to be "both." Many thanks to all, particularly to Dana, whose advice was invaluable.
 

Estrada

New Member
Messages
25
Reaction score
0
Points
1
Location
Illinois
Yup, I have a chimney and if I'm recalling the boiler specs correctly, that's the difference between them.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks