More Boiler Business

The Case of the Shrinking Efficiency Rating

Even though I thought I did all the research necessary to make a good decision, I have spent time doubting the choice I made for the boiler. The radiant system was sized using the Manual J calculations for the existing heat loss of the building based on its construction and what we knew from the energy audit. The energy auditor recommended a small efficient boiler that would hang on the wall and I scoured the Internet for product recommendations. I was enchanted by the idea of purchasing both an instantaneous water heater and a boiler in one appliance and found only good things said about the Triangle Tube brand of heaters. I read all about the typical problems with oversizing a boiler and we calculated that the house required about 85,000 btu’s of heating capacity at the Denver design temperature of zero degrees. A condensing, modulating boiler is the most efficient because it allows for cooler water to return to the boiler to boost heating efficiency and it modulates its fire capacity based on an outside temperature reset adjusting to the changes in temperature automatically.

So looking at the offerings from Triangle Tube online and at various vendors, I was pleased that the Challenger was offered at 95% (Pex Supply listed it at 96%) advertised efficiency and 82,000 btu output. This boiler looked like a good fit for our needs. The combi version of the Challenger has two waterways within the heat exchanger, one is 3/4 ” for the radiant heat pipe and one is 1/2″ for the instantaneous water heater, although the water heater loop has priority when needed. You would think that water could flow through both channels and deliver heated water and radiant heat at the same time. The hot water heater (DHW)  has priority, however. The water heater is only rated at 2.4 gallons per minute, but with just two permanent residents and the idea that we would supplement the boiler with a solar water heating system, that flow rate seemed reasonable. And it certainly is for one ENDLESS shower at a time!

But I FAILED to understand enough about boilers when that decision was made to realize that a 105,000 btu input boiler would not be 96% efficient if it was producing 82,000 btu’s of heat under typical piping installations. (Should be closer to 100,000 btu’s of heat.) I did NOT look up the boiler on the Energy Star list either, which is an amazing oversight since I use the Energy Star spreadsheets religiously for choosing other appliances. In fact the boiler came with a half sheet of information that stated that the US rates the boiler as only 90% efficient.

Excerpt from Energy Star Boiler Spreadsheet

I also did not look to see where the boiler was manufactured, (Belgium) which would not have made as much of an impact on the decision, given that the US market is limited for this type of boiler, except then I had to wrestle with European sized compression fittings.

I read that Triangle Tube boilers featured advanced stainless steel heat exchangers but did not realize that the Challenger itself did not have the stainless steel exchanger but a fused aluminum exchanger, and a stainless burner, one of the reasons for its cheaper price and smaller footprint. The Prestige Solo Excellence has a built in 14 gallon high recovery rate (semi instantaneous) water heater and is actually 95% efficient, but it is also about $2000 more expensive, and  although it can hang on a wall it is quite a bit larger both in depth and height so it needs extra support. Apparently the 110,000 btu version is the most popular. Its price is almost double what the Challenger 105 costs.

I’m not sure what boiler I would have chosen instead and don’t find anything now that has the features I wanted and is as inexpensive. But it really bothers me that I thought I was buying one of the most energy efficient heaters on the market, when that honor actually goes to the Lochinvar Knight according to the Energy Star spreadsheet.