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Old 04-12-2008, 11:34 AM
Senior Member
Join Date: Mar 2006
Location: Northern Lower Michigan
Posts: 2,595
Default RE: Converting Oil Furnace to Gas

LI Sound Grunt - 4/12/2008 6:22 AM

Whoever does your install should do a heat loss calc on you house to see what is actually needed. We find that the vast majority of boilers and furnaces are oversized by a large amount. This is a huge fuel waster.

Hey you sound like you know what you are talking about..... Can't an oversized unit be made more efficient by putting in a smaller nozzle and thus increasing the time of heat transfer and lowering the stack temperature? Also, if the unit is "too small" is the only downside that the house will take longer to heat up (and myabe never make it on the coldest day)? - or is the too small unit inherently less efficient? Another question, my son had a hot ait gas unit with airconditioning. For safety reasons alone (he has propane) he is considering changing to oil - Could an Oil/Hot air system still use the same air conditioning system?
I hope I sound like I know what I'm talking about. I'm in bad shape if I don't because that's what I do for a living.

You can drop a nozzle size on oil with no ill effects in most cases. Some boilers and furnaces are in fact designed and rated to handle multiple firing rates. Much more common to find it on a boiler than a furnace. You may be able to determine if yours is capable of that by looking at the data plate on the unit. It may say something like firing rate .85 =119,000 1.00= 140,000 1.10 = 169,000. It really depends on the design of both the system and the boiler.

As to the second question......Most modern forced air oil furnaces will handle A/C nicely. Most of the older designs will have problems due to insufficient blower capacity and the wrong electronic components. These would be designs that are over 10-15 years old. If you're replacing one just ask whomever you are getting it from. They should know. If they don't, it's time to find another furnace man.
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