A sweep is as lucky as lucky can be.

August 27, 2007 12:39 PM

Varied estimates on the necessary steps to convert from oil heat to gas heat. How do I figure out who's right and who might be trying to cheap out?

Our new house was built in 1890, and when we got it inspected, the inspector noted that the boiler was really old, and beat-up, and leaking a bit. So, we planned to convert to gas heat from the current oil boiler (there's already natural gas in the house for the stove and the hot water heater). After closing, we got estimates for installing the new boiler and removing the old one. Two different plumbers gave us estimates around $4000, but one of them is pushing to install a new flue liner, and one is pushing NOT to install a flue liner. We asked our realtor said it's unnecessary, and our home inspector, who says it IS necessary.

Further confusing the matter is the fact the chimney was repointed when the roof was redone a few years ago, and it appeared from the outside to have a clay liner. So, we decided to have a chimney sweep come to inspect the chimney, and it turns out that there's nothing whatsoever.

So, here's what the numbers look like (cost of boiler is now negligible compared to the labor and parts of installation of all this, and we are not changing away from the steam radiators in the house currently):

Contractor A:
$2950 for boiler installation
$800 for flue liner

Contractor B:
$3500 for boiler installation
$600 for 'fan in the can' if city inspector deems it necessary
believes that liner is unnecessary

Chimney sweep:
$2500 for flue liner, specified as stainless steel and full length
believes contractor A's estimate is extremely low

posted by mkb to Home & Garden (8 answers total)

I can only share my own experience doing this 7 years ago. I got a good Weil-McLain boiler (one of the best purchases I made as a homeowner) and had the flue liner installed. I was told by a few bidders that not installing a liner is the best way to get your house filled with smoke and possibly carbon monoxide. Research what boilers your bidders want to put into the house and go from there. If A and B seem similar, I'd go with A.
posted by yellowcandy at 1:16 PM on August 27, 2007

Response by poster: The boiler is the same model in either case. The gas company (Keyspan) is actually selling the boiler and referring us to plumbers.
posted by mkb at 1:22 PM on August 27, 2007

Modern gas boilers are very efficient, and some can be used without a chimney (direct venting types). However if using a chimney it should be lined because of moisture in the exhaust, and the tendency of that moisture to cause failure of the mortar and brick.
posted by Gungho at 1:29 PM on August 27, 2007

Oh, and I got a similar quote of $2600 to install a keyspan boiler. I passed (for now) as my oil fired Weil mcClain is still working.
posted by Gungho at 1:31 PM on August 27, 2007

Best answer: You really really want a liner (must have) any time you are venting any fuel using device up the chimney. Just like tuck pointing the chimney crown to repair/stop water damage, a liner will help prevent damage to the inside of the flue. Burning natural gas releases a lot of moisture and fumes that you want out of the house now, not condensing in your moisture loving chimney (think acid rain). Please note a Clay liner is not enough anymore, even if you had one.

Be sure it is a full length liner without joints or connections in the flue, at those prices it had better be.
In my area aluminum liners are used for venting gas devices up chimneys, insulated stainless steel liner is used for wood and oil burning devices. Some areas have wicked gas that requires SS liners but that is the exception.
Realtors generally do not know wtf they are talking about when to comes to "proper venting".
The guy pushing for no liner is lazy and dangerous, i wouldn't let him plunge my toilet.

"The boiler is the same model in either case" Good, look it up, find the manual, read the chapter on venting, What does it call for?

If the device is "direct vent" it still needs two vents but may go through the wall or up the chimney (one for combustion air, one to exhaust). Direct vent is preferred.

Also if you have not, time to upgrade your co2/smoke detectors, before the "conversion" because shit happens and we don't want it to happen to you.
I am a hearth/heating professional, but I am on vacation so i will stop now as it's 3pm and time for a cocktail.
posted by blink_left at 3:22 PM on August 27, 2007 [1 favorite]

We asked our realtor said it's unnecessary, and our home inspector, who says it IS necessary.

I'm going to side with a home inspector over a realtor on issues like this, but the one you should really ask is a building code engineer from your region.
posted by davejay at 3:53 PM on August 27, 2007

Building code has about as much to do with safe building as traffic laws have to do with safe driving. (Good ideas, but designed by committee!) City inspectors may be well-intentioned, but at the end of the day, their responsibility is to a rulebook, not to you. Obviously the real estate agent, who has no training in such matters, wants to minimize the financial sting so you won't feel sour about buying the home. The plumbers (?!) who quoted the job have a profit motive.

The independent home inspector works for you, and has no vested interest in any answer other than the one that keeps you alive, safe, and happy. Trust him, or get a second home inspector, or an HVAC expert.

In general, old boilers that moved their exhaust by convection didn't need liners, because the exhaust was so hot, moisture wouldn't condense by the time it got out. But newer high-efficiency heat exchangers extract more energy, leaving the exhaust cool enough that it can condense in the stack. That by itself is a problem (because of the low pH), but it's even worse when the boiler shuts off and the chimney cools down, because water in the cracks freezes and attacks the masonry.

Even newer designs, with even more effective heat exchangers, harvest so much energy that the exhaust won't even carry itself up the flue. They use electric fans to move the exhaust, which begins condensing almost immediately. Liners are somewhere between "a very good idea" and "absolutely mandatory".

Better idea: Ask each opinionated party to back up their assertions with industry journals, government research, manufacturer's documentation, or whatever non-anecdotal evidence they can muster.
posted by Myself at 11:57 PM on August 27, 2007

You might also want to consider a high efficiency boiler (Weil-McClain makes a very nice one (I just installed one in my place (link to the model) and am very happy with it). These 'high efficiency' boilers are more expensive (how much so will vary according to size) but they have two big advantages - first, obviously, is that they let very little heat go out the chimney (your 'chimney' from this will be PVC) because that heat is being reclaimed... which is smart as you are burning the gas for the heat. Secondly is what is called an "Outdoor reset" or a "temp. reset" and what that does is vary the temperature of the water in the radiators according to how cold it is outside... Very cold, boiler is full-on, not very cold, boiler is not full on.

Lastly, I would recomend you get more bids. On the McClain site they mention contractors, that might be an option. Ask your neighbors, ask your realtor, ask the home inspector guy. Get as many as you can bear - part of being a contractor is going around looking at jobs so don't feel weird about getting what might seem like an inordinate number (say, a dozen). This way you have a greater chance of finding a contractor you like and you will see the span of prices and thus have a better sense of what is reasonable, what not.

Good luck.
posted by From Bklyn at 1:22 AM on August 28, 2007