Looking for a boiler, recommendations

[brian89gp]

I am looking for a boiler and wondering if anybody has any recommendations. Boilers are not common at all in these parts so I am pretty much limited to internet research and purchase

Purpose:
-Run radiant floor hydronic system
-Snow melt for concrete stairs and sidewalk in the future (300-400 sq/ft)
-Already have a direct vent gas water heater that will handle DHW duties
-Will handle roughly 1/3 of heating load of house, fireplace does the rest. Will kick on at night and off/on during day depending on outside temp.
-Have water-to-air coil and blower to heat detached garage. Very high intermittant heat load, when I am in there I turn it on, when I leave I turn it off. 4-car

Desires:
-natural gas
-simple, cheap, reliable. Don't want anything too fancy
-all of the electronic controls and increased price of a mod-con turns me off to the idea
-outside air intake (think they call it sealed combustion??)
-prefer power/direct vent to outside wall
-would consider a standing pilot, but a electric ignition is preferred
-staged output would be nice but not opposed to having two smaller boilers instead (Murphy hates me, spares are good...)

Coldest design day heat loss of the house is 200k BTU (very large old house). Average with the fireplace going is around 40k BTU. Garage is around 60k BTU on the coldest design day but would likely average in the 30k range.

With cheap natural gas prices and the low heat load with the fireplace going the operating savings of a 95% over an 80% efficient boiler will never pay back the increased cost of the initial purchase.

 

[woodgeek]

Your math is kinda confusing. If your design load is 200 kBTU/h, what kinda fireplace covers 2/3rds of that? IS the 60k for the garage included? That is, your design load for the house is 140k, and if you wanted to heat the garage on a design day then it would be 200 total? Or would that be 260??

Boiler price is fairly insensitive to size....so if you are spending money now, it probably makes sense to cover your entire design day house load (less the garage). What is that? Good for serious backups when life throws you a loop or at resale.

With the loop in the unheated garage, you would need freeze protection on the water loop, which IMO is a big PITA. A better option might be a wall mount sealed combustion NG unit for the garage, which is pretty cheap, Murphy-friendly and could heat you up fast.

For the balance of the system, we need a BTU output to go further. If the load comes in small, you could even use your DHW system, maybe with a buffer tank added.

For the snow melt....think electric. Have you researched this? IN my reading, they are not magic....if you have 3' of snow it doesn't disappear at the touch of a button. You still have to shovel, and the melter is good for icy conditions.

 

[brian89gp]

I apologize, things always seem clearer in my head .

House:
200k BTU on the coldest day design temp (-17*). Average winter day is much less, around 80k heat load for an outside temp that rarely goes much below 20* and overnights rarely get into single digits. My gas bills have been averaging 1/3 the CCF used previous years, thus the fireplace covering about 2/3 of the average heat load (I reload at 450 and cruise at 650-700, blower on high, so 2/3 is realistic). On the coldest days/nights though the fireplace doesn't even come close and both furnaces are running almost constant. Size of the boiler to handle 100% of the house load would be around 200k BTU to meet the -17* design temp. 200k was arrived at by HVAC CALC and verified by running a manual-J and is consistant with what I see with the existing furnaces.

Garage:
Garage is not figured into the 200k. I'll look into the sealed combustion for the garage, what you suggest makes sense.

Snowmelt:
I will look into the electric versions. My house sits 30' off of the street and the front door is about 20' above sidewalk/street level, it is quite a flight of stairs up to my front door. It is on the downhill side of the property and east side of the house. I have a real bad problem with either surface ice glazing any frozen precipitation on the stairs from the morning sun then the afternoon/evening sun melt the stuff on the south/west sides which run to the front and freeze (yard almost 100% concrete, to the front is the only place to go). A lot of places have enough water running over them that any applied salt will be gone in 24 hours. Its too warm here for snow to stick around for very long, what usually happens is most of the snow melts before the next cold snap and the rest is left as ice. The stairs are falling apart and need redone and the sidewalk is sloped pretty steep due to a poorly planned DIY job so it all needs to be torn out and replaced. My options are pretty open as to how to heat it.


-Natural gas is signifigantly cheaper then electric which is why I was considering it for snow melt. If my math is right, $0.035 per 1k BTU for electric and $0.005 per 1k BTU for gas. ($0.12 per KWH and $0.60 per CCF)
-The need for a rather large single 200k boiler that on average would normally only have 100k or less load concerns me due to short cycling. Thus the multi-stage or multi smaller boiler scenero.
-The weather here is not consistantly cold, winter is a bunch of cold and warm snaps with the inbetweens being in the 30's. It does get frigid (single digits and below), and does get warm (60+), but neither happen for more then a week straight usually.

 

[brian89gp]

For example, the Burnham SCG series boiler is appealing. Sealed combustion, 84% AFUE, power/direct vent, cast iron, minimal electronics, and available in large sizes. My only holdback is if for example I get the 210k BTU model how do I prevent the short cycling that is bound to occur in the more mild months and when the fireplace is going? At 179k output, a 40* rise in a 40 gallon buffer will only take 4.47 minutes plus the run time required to bring a heating zone up to temp.

The Weil Mclain GV90+ is equally appealing. 91% AFUE condensing but still little to no electronics and cast iron. The largest one is on the smaller side though with only 161k BTU output.

A mod-con would sure be easier in that regard. It is hard to justify the $2k price difference though. With the boiler providing all of the heat and doubling today's natural gas prices a 15% increase in AFUE only saves $150 a year in gas. The equipment is going in the basement which is also minimally heated so the standby losses would be put to use.

 

[woodgeek]

I share your concerns about the short cycling....I've seen small (80-100 kBTU output) modcons that were designed to be ganged together to give stages of heat....

On the ice melting....agree that NG BTUs are cheaper. You could use a HX between the domestic loop and a glycol-filled outdoor loop. Might reduce the glycol volume and it might last longer at the lower temps...

Might want to cross post to the boiler room.

 

[jharkin]

Another place to go for advice is the forums on heatinghelp.com