[Greenbuilding] Fresh air to boiler questions

Thu Jan 15 10:11:38 CST 2015

Hi, Ben--

Out here the common setup for gas and oil furnaces has been a horizontal duct with a gravity damper. The damper closes off outside air when furnace not running. A better solution is a low-voltage motorized damper (which you can install). This at least reduces the continual air leakage of an opening like you describe. 

Sometimes unintended air leaks in a basement act as a dehumidifier for moisture, something to consider.

Best, Mike
Sent from my iPhone

> On Jan 15, 2015, at 6:41 AM, Benjamin Pratt <benjamin.g.pratt at gmail.com> wrote:
> 
> Norbert.
> There is no damper of any kind. I could add one, but there isn't much room beofre the brick chimney. Perhaps on the horizontal portion, if that is acceptable.
> However, I am still considering a new boiler. Does anyone have any input as to my original question--what would be the ROI on a newer more efficient direct vent boiler? I just found this link, but have no way to determine if it is accurate. 
> http://www.houseneeds.com/learning-center/hydronic-boilers-learning/boilers-heat-source-costs-example
> Thanks!
> Ben
> 
> 
> 
> 
> b e n j a m i n p r a t t
> 
> professor art+design
> the university of wisconsin stout
> 
>> On Thu, Jan 15, 2015 at 7:40 AM, Norbert Senf <norbert.senf at gmail.com> wrote:
>>> On Wed, Jan 14, 2015 at 4:36 PM, Benjamin Pratt <benjamin.g.pratt at gmail.com> wrote:
>>> Norbert, I would love to close off that 6" hole. I was told that the boiler would operate less efficiently if I do that. I suppose that assumes less oxygen
>> 
>> not true, common fallacy. In some jurisdictions, building code may require it, or it may be in "manufacturers installation instructions", so you need to check that.
>> Only exception I can think of is a separate, sealed, furnace room. Always make sure you have a CO detector, since low level CO spillage is very common with your type of setup, outside air or not.
>>  
>>> IF that is not true, I and am ready to plug up that hole! Any ideas about the open flue of the boiler and the water heater? Are they less concerning?
>> 
>> Not sure, since my experience is with wood and not oil or gas. In a basement, you are very likely to have negative pressure, so on standby perhaps there is not a lot of flow from the basement into the barometric damper, particularly if you have an outside chimney. If you take a sheet of old style newsprint, it has a grain orientation to it, and in one direction you can tear it into parallel strips. This makes a handy flow visualization tool, for example low flows into open fireplaces. It might be interesting to check around your barometric dampers, air inlets, window drafts, etc. A stick of incense, or a cigarette, is good also ;-)
>>  
>>> Thanks!
>>> Ben
>>> 
>>> 
>>> 
>>> 
>>> 
>>> b e n j a m i n p r a t t
>>> 
>>> professor art+design
>>> the university of wisconsin stout
>>> 
>>>> On Wed, Jan 14, 2015 at 3:04 PM, Norbert Senf <norbert.senf at gmail.com> wrote:
>>>> The air consumption of an 80,000 BTU/hr boiler is in the range of 25 cfm while it is operating. Heating that combustion air by 50 degrees F requires about 3,000 BTU/hr, which happens no matter whether the outside air has a direct or indirect path to the burner.  Having a 6" dia permanent leak in the basement is a really inefficient way to do it. There is no good engineering reason to have that leak, unless your basement is hermetically airtight and 25 cfm would depressurize it enough to cause the boiler or water heater or (worst case) an open fireplace to backdraft. This is generally considered to be -5 Pa. Much more likely that a 250 cfm kitchen exhaust hood would do it, assuming that your basement is not sealed from the rest of the house. Clother dryers and bathroom fans also, are in the 100 cfm range.
>>>> 
>>>>> On Tue, Jan 13, 2015 at 7:43 PM, Benjamin Pratt <benjamin.g.pratt at gmail.com> wrote:
>>>>> I have been sealing up and insulating the unfinished portion of my basement, but am concerned it is a waste of time and money: There is a 6" fresh air duct to provide proper combustion for the boiler. Also, there is no damper on the water heater or boiler. Therefore, a lot of cold air is continually dumped into the basement, and a lot of hot air escapes up the chimney.
>>>>>    I suppose the solution to this would be to install a new boiler, and to install a direct vent kit on the water heater. The boiler is around 15 years old, and is 84 percent efficient. If I buy a more efficient boiler, that is direct vented, any guess as to how much energy I will save? I suppose its more then just the amount of natural gas I will save with a more efficient boiler, since I would also be eliminating a huge source of air infiltration. I would like to be able to calculate the ROI, so my wife agrees to the purchase.
>>>>> I'd appreciate any help you can provide.
>>>>> Thanks,
>>>>> Ben
>>>>> 
>>>>> 
>>>>> 
>>>>> b e n j a m i n p r a t t
>>>>> 
>>>>> professor art+design
>>>>> the university of wisconsin stout
>>>>> 
>>>>>> On Tue, Jan 13, 2015 at 3:46 PM, Sacie Lambertson <sacie.lambertson at gmail.com> wrote:
>>>>>> I'm looking for an architect in Seattle who understands energy efficient good building and does contemporary design work.  Welcome suggestions.   Best to send these off the forum, to me directly. Sacie
>>>>>> 
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>>>> 
>>>> 
>>>> -- 
>>>> Norbert Senf
>>>> Masonry Stove Builders
>>>> 25 Brouse Road, RR 5
>>>> Shawville Québec J0X 2Y0
>>>> 819.647.5092
>>>> www.heatkit.com
>>>> 
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>> 
>> 
>> 
>> 
>> -- 
>> Norbert Senf
>> Masonry Stove Builders
>> 25 Brouse Road, RR 5
>> Shawville Québec J0X 2Y0
>> 819.647.5092
>> www.heatkit.com
>> 
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>> Greenbuilding mailing list
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