? About Propane Furnaces

suitcase_sally · #1 08/17/12, 10:36 AM

This is a question for the furnace/boiler people here.

I'm in the market for a new boiler this year and could use some help with my choices. Here are the two that my furnace guy offers:

Dunkirt PWXL-4E Standard efficiency

Knight KBN106 High efficiency

The standard one has a cast iron heat exchanger with 20 year warranty.

The high efficiency one has a stainless steel heat exchanger with 12 year warranty.

The high eff. one costs about 60% more.

My question is basically, will the high eff. one wear out faster? Should I be concerned about the lesser warranty on the high eff. one?

Are there many problems with the high eff. boilers?

geo in mi · #2 08/17/12, 11:34 AM

I bought the Dunkirk hi effeciency boiler, but it had a cast aluminum block(fire chamber and heat exchanger tubing), as a changeover from oil to natural gas boiler. You should look at the warranty, though--usually it covers the block only, and doesn't include the cost of shipping or teardown/reinstallion if it goes bad.... What happened to mine was that the block had a soft spot in the casting and began to leak. The reinstallation cost was $700, even though the new block was no charge.

Efficiency of 90% will extract just about all the heat out of the gas and allow you to vent exhaust gas thru the foundation by PVC pipiong, rather than a hot chimney as is the case with the lower efficiency. The ten percent efficiency should be factored in, especially if propane continues to go higher.Also, you will have to have a small pump--or else a floor drain to get rid of the water vapor a high efficiency gas furnace gives off while burning.

geo

suitcase_sally · #3 08/17/12, 12:47 PM

Yikes! My house is built on a slab and there is no drain. Doesn't the water go out the exhaust pipe? We have a propane furnace in the pole barn and the water vapor goes out the piping that goes out the wall.

The Dunkirk is supposed to be 80.1% efficient, the Knight, about 95%. I'm wondering if the 15% difference justifies the $3,000.00 difference in price.

farminghandyman · #4 08/17/12, 01:04 PM

If needed a condensation pump can be used to pump the water out of the furnace area to a drain or dry well,

the High efficient furnaces take more heat out of the flue gasses and the water vapor will condense out of the flue gas, a lower efficient furnace will not cool it to the point of condensing,

suitcase_sally · #5 08/17/12, 01:56 PM

Oops! Dh says the water vapor is not going out with the exhaust - it has a separate pipe.

plowjockey · #6 08/17/12, 02:22 PM

It's summer and propane is still over $3 gallon.

Frankly I'd go with the one, that costs less to operate, figuring in the payback for the 60% more cost.

geo in mi · #7 08/17/12, 02:31 PM

Installation cost for either unit will be the same, so the price difference between the two furnaces alone can be measured against the 15% savings in propane each year, times the number of years to find the payback.

geo

bja105 · #8 08/18/12, 03:02 PM

I sell, service, and install boilers for a living. If you can afford the high efficiency, go for it. Just make sure you get a contractor with experience with the condensing (90+) boiler. There are lots of differences.

Don't worry about the drain, that is what condensate pumps are for.

Besides the improved combustion efficiency, the condensing boiler brings in it's combustion air from outside, reducing infiltration of cold air. Most condensing boilers have a modulating firing rate, factoring return water temperature and outdoor temperature to decide what the target supply water temperature is, and modulating the firing rate. That is a big increase in efficiency.

I have no experience with the Lochinvar Knight, but it is the boiler most often raved about by heating pros. Find a good contractor, and follow their service recommendations, and you will get good service for years and save money.

If you are on well water, make sure the contractor knows it ahead of time. Some manufactures recommend different procedures. I know our brand (Weil McLain) ships a system stabilizer, a coating for the inside of the pipes, with every boiler.

The 60% price difference is about the same for our cast iron versus cast aluminum boilers.

bja105 · #9 08/18/12, 03:07 PM

As to longevity and breakdowns, the high efficiency has many more parts, and most of them are more expensive OEM-only parts. Figure a 20 year lifespan for the cast aluminum, and a 25 year lifespan on the cast iron. That is with boilers, furnaces are different, and neither 80% nor 90+ furnaces will last as long as a boiler.