Power Vent furnace type compatibility

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Old 09-23-04, 08:34 AM
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Power Vent furnace type compatibility

Hello, I have a problem with a Power Vent system on an oil fired boiler heating system. The home is less than 1 year old. There is a high pitched screaming noise which originates from the power vent when it is operating. I notified the builder who sent over a company man who originally installed the system. Despite my recommendation to replace the unit, he disassembled it and claimed all it needed was to be cleaned. The unit was quiet for a few weeks and then started the noise again. I again contacted the builder who again contacted the heating company. The heating company guy told him that the furnace needed to be cleaned and serviced because it was running too rich and that was what was causing the problem with the Power Vent. The builder did not believe that was the issue being a new system, but agreed to pay for the service call/cleaning. I called my regular heating guy I have used previously, and he told me several disconcerting things- first that a Power Vent system is not compatible with most oil fired systems. He claimed they are primarily for Gas furnaces. He then said he will not even work on such a combination due to prior bad experiences, several of which concluded in legal litigations resulting from his opinion that the two are incompatible. He further stated that the reason the builder would put a system together is cost only- to avoid having to build a proper chimney. He asked if we had any problems with soot accumulation in the vicinity of the furnace and we do indeed have a minor amount that does accumulate. His recommendation is to push back on the builder and insist that a proper chimney be built to replace the incompatible Power Vent. My question is to ask if his assessment is reasonable, if in fact a Power Vent does not belong on the system, and if his solution to replace it with a proper chimney is the right way to fix this. Thanks very much, sorry for such a lengthy posting.
 
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Old 09-24-04, 09:50 AM
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With todays builders, it is not uncommon to see powervented oil boilers and furnaces. There is not a compatibility issue, but for technicians who cannot fully comprehend the adjustment sequence and procedure for a power vented system, it can lead to problems. The first requirement that I have before agreeing to powervent a system is that outside air is used for combustion. That way there is no pressure difference between inlet and exhaust pressure. Second is that in our area, I will not install the exhaust on the West wall which is the direction of the prevailing wind. And a high density oil filter must be part of the oil system to prevent nozzle clogs. Other than that, it is all in the details. The burner needs to have a control that provides pre-purge and post-purge. The vent pipe through the wall should go through the concrete if possible as opposed to the wood. That is for noise reduction. Some new systems have isolated the inducer motor from the vent pipe very well and some even draw combustion air through a coaxial pipe around the flue. However, the old noisy and cumbersome power venters are still available and are less expensive than the high quality ones.

When it comes to burner adjustment, draft works best set around -.10 wc at the breech and CO2 should not be set above 10.5%. This detunes the efficiency slightly but will result in trouble free operation throughout the year.

Hope you get your problem resolved.

Ken
 
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