Hello,
I happened upon this website earlier today and have been searching through the forums to see if this question has been posed, I apologize if I am repeating a topic which has already been covered. I must say, I have found a great deal of information on here that is very useful for my situation! :)

I am looking for some opinion on my home situation before I hire a contractor (have quotes and product narrowed down to a point), but have to make a decision and have one item impacting this.

Briefly, I live just outside of Toronto, Ontario, Canada and bought a mid-60's backsplit in March of 2010. The house currently has a Slant/Fin, atmospheric boiler (130,000 BTU approx), which would not start up this fall. In November, during a very cold week, the thermocouple needed to be replaced, which was done the following day, however, due to it's age (45 yrs approx), and our incredibly stringent standards regarding atmospheric boilers, I have to have major work done on it (and the exhaust stack) and have it retested within 90 days or will be fined. Instead of spending lots of money on a band-aid solution, I have decided to buy a new modulating, direct-vent condensing unit.

I have received pricing from 3 contractors, on 5 different units, and have narrowed it down to either a Triangle Tube Solo 60 or a Solo 110. I have been doing hours and hours of research on forums and other websites over the last month and a half, and am confident with the decision to go with Triangle Tube (unless someone can give me a real good reason not too!!! :). i will be taking advantage of the fully modulating capability and outdoor reset, etc.

One contractor has performed a heat loss calculation and determined 44,000 BTU is my number. The house is approximately 2,300 square feet, including 2/3 of the basement being finished into a rec room, an office and a 4-psc bathroom. The balance is storage and laundry/DHWT/boiler on concrete floor. The house has 1 1/4" copper tube and baseboard radiators with aluminum fin. There are cold areas of the house, particularily the front bedroom and front living/dining rooms (open concept). We also just replaced all of the windows in the house in October.

I just replaced the DHWT in April, with a new EnergyStar unit (rented, no cost to replace) and don't want to get into a combi or indirect water heater at this point, as the cost to remove this unit and return it is too high until it is more than 3 years old (as per the rental contract). I may consider adding an indirect water heater in the future but not now.

My questions are:

1. if the heat loss calc indicates 45,000 BTU's, will the Solo 60 (approx 60,000 BTU) be sufficient to heat the home, especially during the potential 2-3 weeks (or more) of -20 degree Celsius cold in the winter every year?

2. Is the Solo 110 a better solution? Theoretically, since the unit is modulating anyway, does it really matter if I go with the larger unit?? Is this a bad decision???

3. I suspect it will be at least 2 more years before I would consider putting in another DHWT (indirect), if at all - I don't know how long I will stay in this house, but hope it will be for a long time unless something changes/happens. While planning ahead and going with the 110 would be better for the indirect water heater use, I may not actually end up buying one down the road.

Sorry for the long-winded post, but I certainly appreciate any feedback on choosing the right sized boiler!!!!

Thanks in advance!

Sagacious question.

You have done your homework and good for you.

Choosing a contractor that produces - or offers to produce - a computer generated heat load analysis is the first smart step regardless of country or climate. This standard alone eliminates 9 out of 10 heating contractors in the US.

The heat loss sounds correct for the information given and the 60 will certainly serve. There are very few situations where a space-heating boiler should be sized up for DHW. Remember the average water heater holds 40 gallons and has a 40mbtu burner running about 20 minutes a day.

As to sizing and modulation; nearly half the HVAC equipment installed in residences in N. America are oversized by more than 20%. This wastes fuel and makes homes more uncomfortable. What's more is that condensing boilers will not suffer short cycling like their primitive cast iron cousins. Service and fuel efficiency will suffer.

Yes, the 110 will modulate down to its low-fire (30mbtu) but since this is so close to your design load it will bump off the bottom most of the season. This is especially true in the shoulder seasons when modulation and outdoor reset are most advantageous.

While it is true that we must size the heat source and radiation for the coldest 5 days of the year sizing the boiler as close to outdoor design conditions is the only way to yield the true potential of a ModCon boiler i.e. comfort, fuel economy and efficiency.

PS Don't forget to measure the radiation and check the boilers high operating temperature for compatibility.

A Solo-60 would still be putting out over 50K at 180F water temps (~85-86% thermal efficiency at LEAST), should the radiation demand that under design conditions. It's DOE heating rating is 54K (90%). (The I=B=R rating of47K presumes high losses into unconditioned space that may be irrelevant- sort of a worst-case situtation.) That, plus the oversizing safety-factor built into most heat loss calc packages (15-25% typical) means you'd be good to go with the smaller boiler. With a min-modulation roughly half that of it's bigger brother it'll run more efficiently, running fewer than half the burn cycles, and thus have fewer maintenance issues over time.

IIRC The TT Solos come preset to deliver 180F water @ 0F outoor temps, but it's a programmable/tweakable parameter- setting it to the lowest value that delivers the heat gives the best overall efficiency. Most old-school radiation is a bit overdesigned anyway, and you probably wouldn't need more than 160F water (TBD) giving you a bit more margin on the boiler since it gains efficiency at lower temps. Optimizing the reset curve is necessary to get the best effiecency and best comfort out of the thing, whether YOU do it, or the installer does. The heat loss calc is just an estimate- the fine tuning is sometimes best done empirically.

With fin-tube the radiation output curve gets a bit funky/less predicable when you go below ~120F. Setting it up initially during mid winter means you may have more tweaking to do come spring, when the heat loads (& water temps) are low to get good results with fin tube. (Cast iron baseboard is much more linear at the lower temperature ranges, but 3-4x the cost of fin-tube.)

Get the 60.  When you switch to an indirect, upsize the tank if you have higher hot water usage.

No reason for the larger unit.

 

Good Luck

 

Eric

Thank you very much for all of you points (been sick today, so I haven't had a chance to check these until now).

Badger - your point about the minimum firing on the 110 is well-taken. That is exactly the type of issue I suspected would be the case, hence the question....and yes, I've been doing a LOT of reading. Still not proclaiming to be an expert, but at least I now understand most of how these things work!!!

Dana1 - I was thinking it would be set around 160F, for the most part, as I could see how a higher temperature wouldn't really be beneficial or efficient. Right now, with the "broken" Slant/Fin, it is only achieving about 115F at most on the output thermostat gauge, since the thermocouple was replaced, but the house is warm most of the time, until the outdoor temp drops to about -10C or lower, then it can't keep up/compensate and the house sits around 18 or 19C (sorry, can't convert to Imperial off the top of my head!!)

So, then I assume the TT is a good unit, as none of you mentioned any anti-TT comments? I will let you know how it all goes!

Thanks again, I really appreciate your comments.
Cheers

A cast-iron boiler running 115F output will die pretty quickly from condensation corrosion. A copper water-tube boiler could go quite awhile at low-temp, but you clearly need to run the baseboard at higher temp to be able to deliver the heat.

But if it's still keeping up at -5C outdoor temps with 115F output, you probably never need to boost the output temps curve higher than 140F @ 0F (-18C) outdoor temps.

Triangle Tube has a good track record- as long as you have a decent installer and local distributor support you won't be sorry. There are many good boilers out there, but none are any better than the installer/system designer (and if the installer has to wait 3 weeks to get a part, that's not so good either.)