My dad and I were discussing this yesterday, the pros and cons of changing the NG. The cons disappeared when he offered to pay for the $7500 hook up cost. I'm now going to start looking at NG boilers and searching for a competent installer for the brand of equipment I select.
I will go back and read deeper, but I read somewhere that high efficiency boilers aren't actually high efficiency in some areas due to outside temps. I will need to look at a combi-unit or get a hot water heater as the current boiler serves both functions. Anybody have any recommendations? I have read some reviews that say the Bosch equipment is pretty good provided the installer is familiar with the equipment and follows the instructions on proper set up.
It's not the outside temp ... it's the water temp.
Modern modulating wall boilers have a small amount of water around a combustion chamber. The only way to get above mid 80% efficiencies is to use a secondary heat exchanger and pass the flue gases though that second exchanger. This reduces the temp of the flue gas (that normally would go up the chimney) -- this is how they get up to 96%. This exchange cooling is done with return water. In a radiant system -- since the water is not very hot to begin with the water coming back is cool enough to cool this flue gas. That's why they call them "condensing" -- that's what they are doing ... and lots of water comes out of the gas -- burning NG makes CO2 and H2O. A forced air furnace has no problems ... as the return air is cold and can easily cool the second exchanger.
Older type boilers had simple burners under heat exchangers -- some cast iron ...others used copper fin coils. As advancements came along -- they added fan induced combustion to those units -- this allowed for outside air make-up to be used ... preferable in a tight house.
Many old houses use high mass heat exchangers - CI radiators or baseboard ... they are sized based on very hot water. Same with copper fin tube ... often 180 degrees minimum. Also the old CI boilers did not like cold return water. So the systems ran at 180 degrees ... in the NE USA .... since the boiler was running most of the time they would install a coil and heat the hot water that way.
When you go to a modern wall hung condensing boiler -- they often max out under 180 degrees. So you have to be careful of the sizing of the radiation ... if you need 180 to stay warm in the coldest time of the year .. you may not have it.
Also -- since you have all this very hot water -- the return water coming back to the boiler is not hot enough to "condense" in the wall boiler ... so you don't get all of those savings.
The above is why I kept the old style boilers in my Chestnut Hill Home. The house was all CI radiators -- lots of water. Needed high temps when it got cold out .. the basement was a basement. The house was built in 1905 -- so it leaked.
I had no need for induced combustion. Mine have simple flue w/ vent damper. Buderus CI boilers are special in that they can take colder return water -- so they can be set up for outdoor reset. It's a shame -- the older CI boilers are going away in the name of efficiency .. but the savings in many old house situations are small.
You need to do a heat load on the building and figure out the radiation .. what you have and what temp water it needs. You have a history with the oil burner -- so you can guess on the efficiency and do a conversion to NG cost.
If you are going to spend 2k a year on gas .... and the potential saving going to 96% are 10-12 percent ... What's $225 ? I was looking at maybe 300-400 savings .. and the equipment was 10-12k more at the start. That's a 30 year payback -- and no wall hung is going to last 30 years w/o service .. and replacement. The old school CI boilers will make 30 years. My first Buderus install is still going strong from 1994 .. new relay and vent damper motor ($400 in parts) .. the system has needed other maintenance (circulators) .. but they go regardless of boiler. The boiler can also run an indirect tank.
I say the above .. because "new" is not always better.
I'm building a new house -- very tight (foam)... no space anyplace. Propane is my only fuel. The house will be all radiant -- so i am doing a wall hung in this house.
