negative pressure ?

TomM

I am installing a bradford white power vent gas water heater 40000btus..This is replacing the h/w coil on my 150,000 btu steam boiler w/ tjerlund power vent.  The boiler has a beckett burner @ 1.0gph.  .When do I need to start worrying about negative pressure issues?  The basement is 26'x16.  I'd like to tighten it up later.  .I'm worried about this because when the boiler runs in the winter, you can feel air getting sucked into the basement thru every leak and from the upstairs. .Would direct vent be the way to go?  .Is there a rule for fresh air supply per BTU?.Thanks!

Tim McElwain

First of all negative

pressure is typically caused by mechanical exhausting in the building. It sounds like you have plenty of air if it is rushing in when things are running so that is the opposite of negative pressure.



That being said with a 26x16x8 = 3,328 cubic feet at 50 BTU's per cubic foot that area can handle about 66,000 BTU's. Any amount over that  it is considered a confined space and must have air brought in from outdoors typically two openings one 12" from the floor another 12" from the ceiling. It is usually 1 square inch per thousand BTU's for both openings.



It looks like you are burning about 140,000 on the boiler and the water heater will add 40,000 for a total of 180,000 that means two openings if directly communicating with outdoors of 180 square inches. The good news is you need less than that when using power venting. You need to get a good technician in to figure out exactly what you need but definitely no less than 100 Square inches is the rule.



Do you have a dryer in the same area as the boiler/water heater?



Another alternative is to use and indirect water heater and have it run off the steam boiler as a condensing zone.

Coany

Beckett fresh air kit on both burners

 use 100% outside air for combustion.

TomM

confined space

Ok.  So i definitely have a confined space.

.Fields has a good writeup on it:  http://www.fieldcontrols.com/cas.php



.

Room size= 26x16x7 = 2900 cubic feet.

and you need 50 cubic feet of fresh air per 1000BTUs.

So, my room will support only 58000 BTU's!  No wonder air rushes into the basement all winter long. 

So if I run the boiler for an hour, the air will have to be replenished over three times over that hour!  Amazing!

I guess i'll go with the power direct vent for the hot water heater and worry about the rest later. 

Thanks!

TomM