Some rambling questions regarding a water boiler replacement dec

Tom_37

I've had four local contractors over for a review/recommendation of my heating system. Now I'm more confused that ever. Wanting to be an informed consumer, I avail myself to the experts:

The current system is the original American Standard boiler rated at 150K/120K In/Out (sixties vintage I'm guessing). Total heating area is about is about 2750 sq ft. Degree Days is about 8200/yr (Wisconsin). Construction is 2x4 with storm windows, and 18" cellulose insulation, 180 ft of baseboard registers wtih 3 zones. From the utility bills for 2003 we used 1500 therms for heating.

1) Most contractors I've had over for a review of my system don't recommend the high-efficiency boilers (90% plus), but are instead recommending the tried-and-true lower 80% efficient boilers (Burnham Series 2) citing the additional cost plus servicing will outweigh the efficiency gains. Sounds reasonable giving the price difference, doe's this make sense??

2)One contractor recommended a "standing pilot" system citing that the heat from the pilot helps keep the system corrosion free. That makes little sense to me as I would assume the boiler manufacturers are aware of the environments their products are placed in and would design them such that there is no need to provide a heat source to maintain proper conditions. The basement is nice and dry and we run a dehumidifier during the summer. Are standing pilots still needed?

3) How about outdoor resets? Is this a more efficient use of money? (i.e. would additional money be better spent on an High efficiency boiler or an outdoor reset?). Again one contractor recommended an outdoor reset over higher efficiency.

4) how about "undersizing" the system, I understand that AFUE ratings are determined with the boilers running in a "steady-state" condition and don't factor in startup/shutdown losses, would a smaller system running longer be better?

5) should I just do nothing? one contractor said my system isn't all that bad, but gee, the area near the boiler is always in the mid-70's while the rest of the house is kept at 67 degrees. Maybe I should move down there!

appreciate any insights. Thanks in advance!

Constantin

Let's do some math...

According to your post, you consumed about 1,500 therms in a 8,200 DDY. Dividing one by the other, converting to BTU, and assuming your old plant had a efficiency of 80%, your heatlosses are something like 14.6kBTU per DD. On a cold day (-15°F outdoor = 80DD) that would require something on the order of 49kBTU of heat per hour to keep the house warm.

All that is assuming you don't use gas to heat water, stove, dryer, etc. If you have any of those appliances, your required heating plant is even smaller than 49kBTU net IBR. In other words, unless you need to heat a lot of hot water for home showering/jacuzzi/waterfall needs, your required heating plant could be a lot smaller than the present one down in the cellar. Anyone else care to do the math? I'm just a homeowner after all!

Since you're heating with gas, I would take a closer look of the costs and benefits of going with a condensing system. I would advocate the combination of a small condensing and modulating wall-hung unit (like the Munchkin T-80) with a well-insulated indirect water heater, simply because the AFUE rating doesn't tell the whole story (think standby losses, no accounting for modulation, outdoor reset, etc.). Furthermore, do not consider the Munchkin on it's own, add a Vision I and outdoor reset sensor to really stay comfortable and save money at the same time.

I'm not a fan of standing pilots though some installers swear by them. That is all moot if you buy a modern boiler, because most of them are happy to use electronic ignition instead of pilot lights.

A smaller system combined with outdoor reset will likely save you a lot of money simply because it won't be cycling up and down all the time. Your present system sounds way oversized considering your gas usage vs. degree days so I wonder how many hours per day your boiler actually runs on a cold day.

Lastly, it sounds as though your present boiler/flue is wasting a lot of energy heating unoccupied spaces. Once again, a condensing boiler could help keeping those areas colder and the rest of the house warmer.

PS: How did you manage to install 18" of insulation into a wall that's just 3.5" deep. Just curious... ;-) Attached is a small spreadsheet I wrote in 5 minutes to do the above math. Does it look right?

Tom_37

thx for the spreadsheet, I appreciate it! Of the four contractors I had over, only one asked about usage, insulation levels, baseboards, etc. His size recommendation was smaller than the rest and match what you're saying. The rest just recommended a replacement closely matching the BTU's of the old one.

AFA the 18" insulation, that's for the attic, reading the original post I could see where it may not be too clear.

thx!