providing combustion air vs freezing the pipes

Originally Posted By: kshepard
This post was automatically imported from our archived forum.



Today I looked into a small (approx. 6’x8’) room with a boiler and water heater in it. Both are gas-fired.


One wall is exterior concrete foundation wall and the vent (taped to the top of the burn chamber with aluminum tape, no draft diverter) vented out the wall above grade.
Another wall backs up to the garage (firewall). The other two walls back up to living space.

There is no combustion air supply except the oversize hole they chipped to route the vent to the outside, maybe and inch all the way around. The door fits tight to the carpet. 10 minute CO reading was 12ppm.

If they bring two 12 inch ducts directly into that little room, those water pipes are going to freeze and burst when it hits 20 below this coming January. If the ducts come in through the heated garage and run for say, 12 feet before going through the wall into the mechanical room the air will warm considerably but the one-hour rating of the firewall will be compromised. Joists run the wrong direction to run through bays.

Any suggestions on how to provide combustible air without freezing the pipes?


Originally Posted By: kshepard
This post was automatically imported from our archived forum.



…actually, probably better if it’s not combustible air but combustion air.


Originally Posted By: Brian A. Goodman
This post was automatically imported from our archived forum.



Kenton,


I’m not very familiar with 20 below conditions, but my first thought is that the simplest thing to do might be to wrap the pipes (insulation, heat tape, etc.). You’ll have to tell me if that would be practical in this situation.


Originally Posted By: kshepard
This post was automatically imported from our archived forum.



Heat tape and insulation combined with the heat produced by the boiler itself might do it. I suppose they could put a small thermostatically-controlled electric heater in there also. It’s only that cold for a few weeks out of the year.


Originally Posted By: Blaine Wiley
This post was automatically imported from our archived forum.



Why can’t they put combustion air vents high and low on the door or an adjacent interior wall?


Originally Posted By: phinsperger
This post was automatically imported from our archived forum.



The direction to go should not to be concentrating on warming the pipes but rather warming the incoming air. If the extremely cold air is delivered to the combustion chamber it will cause impingement ( inefficient burning) resulting in CO.


It can also cause extreme temp swings on as the unit cycles on (warming up) and then during the off cycle (cooling down). This can put a lot of stress on the welds in the exchanger and could possibly lead to a crack ![eusa_doh.gif](upload://has2a0g32D0AAlDjAwVcrg3HnhX.gif)

You mentioned that you did not want to go though the garage wall. Fair enough. What about coming in from the exterior go right through the combustion room into the rest of the house for a bit and then back to the combustion room.

Or more simply put a grill in the door. You will have to look at the rest of the house to ensure that there is not other appliances that would depresurize the house (ie central vac, etc)

All this has to be sized accordingly to the total btu rating of both appliances.


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: phinsperger
This post was automatically imported from our archived forum.



Blaine, I guess I need to type a little faster. icon_smile.gif



.



Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: kshepard
This post was automatically imported from our archived forum.



Both should work. They just spent a lot of money on expensive new doors and are hesitant to provide air by cutting into them.


The garage would provide space for the ducts to run straight far enough for the air to have a chance to warm, but the ducts can't violate the firewall. The other surrounding rooms are finished living space where they wouldn't want ducts showing.

They could come directly into the mechanical room but they would have to make several turns which would impede flow a bit. BTU rating will detiermine whether this'll work.

Thanks guys.