I’m trying to do actual calculation regarding energy consumption.; What I need is someone who can tell me how many BTU’s a 4inch hole in the ceiling will use per hour/day etc.
I have a super well sealed house and I want to keep it that way, the idea of using a gas water heater because of it’s projected lower fuel costs appeals to me but I realize that it would mean a 4 inch (OK 3 inch (I can do the math) hole that draws heated air outside 24/7. In addition the burning of gas would require oxygen from the house creating a mini vacumm incresing the air infiltration. I can then adhust it based on the number of heating degree days and find out the real cost of using gas verses electric heat..
Just for information I expect to use water heaters rather than a boiler, I’ve looked at those numbers and water heaters really make sense..
Replies
>how many BTU's a 4inch hole in the ceiling will use per hour/day etc.
At what outside temperature?
Let's try 10 degrees, I think that would be a fair number considering the swings Minnesota weather goes thru. I do know the average tempurature varies dramatically for the 9 months of our winter, and I'm sure some of those months are actually above freezing <G>
I doubt if it can be calculated.
Flue height, location in the house (which pressure zone,) length of flue, ratio of vertical to horizontal flue, and, very possibly, the phase of the moon {G} can all affect the stack effect when the water heater isn't operating.
You can get closed systems which draw their combustion air from outside.
One model is spec'd here: http://www.bradfordwhite.com/pdfs/residential/103dv.pdf
View Image
Sojourners: Christians for Justice and Peace
I keep running into that same wall, there must be a way to calculate that sort of thing. I'm aware of closed furnaces but to date I've yet to find a closed water heater.
Not sure it would be possible to use a closed water heater, cold air would most likely cause a water heater to freeze (at least up here in the arctic circle) I couldn't calculate the loss of energy in trying to keep water exposed to 40 below air warm enough to take a hot shower..
From a simplicity point it would seem to be just buy an electric water heater and be done with it. or figure that the energy savings you get with a gas water heater is worth the potential loss of heat.
Figure out how much air the unit draws. Presumably someone somewhere has specs on this. Then compute how much it costs to heat that volume of air from outside temp to inside temp.It ain't the size of the hole, it's the volume of air.
What DanH said. That is exactly how to figure it out.Heres a link to an article called "the cost of exhaust only ventilation"http://oikos.com/esb/50/ventilation.htmlThis is a detailed walkthrough of the calculation. You can likely use the calculation worksheet in that link with very few modifications.When we got a new furnace (hi efficiency), my first reaction to the chimney was to also get a new hot water heater (electric in this case). So, now all my combustion appliances are sealed. And I don't have to worry about combustion gasses doing dangerous things if the ventilation fan goes out of control one day.Last year I didn't know what any of this stuff meant.
I believe he's talking about losses from the stack effect when the unit isn't operating, in addition to during operation.And my experience is that air movement up water heater flues varies significantly both before light-off and during and after operation. In doing Carbon Monoxide Safety Analyses I use a draft gauge to measure the draft, so I have some specific, measured experience in actual performance.I have seen water heaters with no measurable air movement before light-off and with more than 0.03wc" of draft
View Image
Sojourners: Christians for Justice and Peace
If one is worried about loss when the heater isn't operating, I'm pretty sure there are still flu dampers available that will cut the flu off. Expensive, though.
Frenchy...does your utility offer dual fuel rates for DHW?. Down here in the banana belt (Fillmore County), Tri-County offers .038/KWH for DWH, and will sell you a 80 gallon Rheem for $99.00...then you have to run a separately metered service to it so they can interrupt during peak usage. They figure that 80 gallons well insulated at 130* will get you through a shower or two if you need to during interrupt.
Frenchy - check out the model I listed and give BW a call.The flue and air intake are "concentirc" the flue runs inside of the air intake, so you get some energy savings from heat transfered from the combustion gases to the combustion air.
View Image
Sojourners: Christians for Justice and Peace
frenchy,
The Rinnai tankless are closed systems, no stack effect. Kinda pricey.
http://www.rinnaina.com/products/waterheaters/index.aspKK
Many thanks for the link...been wondering if the water heater makers had caught up with modern times yet....
Have you looked at the high efficiency models? They are like the 90+ furnaces. Bring outside air in for combustion and have a forced draft.
It has been about 7 years since I installed one, but it would not create a min-vacum in the house. The fan for the exhaust cools it enough to use a side wall vent.
Been a while, so I could be all wet on this one.
Dave
Look into the sealed combustion models. Super efficient, no standby stack losses, and no chance of backdrafting.
Here's one: http://www.americanwaterheater.com/WHBrowser/gas/Polaris50.cfm
Looks pretty cool.I haven't seen any, maybe becasue o9f the price tag. Few people in my area are going to put out 10 times the going price for a "standard" water heater.If Polaris is looking for a beta site ...{G}
View Image
Sojourners: Christians for Justice and Peace
"I haven't seen any, maybe becasue o9f the price tag. Few people in my area are going to put out 10 times the going price for a "standard" water heater."
Certainly a tough upfront cost to overcome.
Though they a gaining a big following as a hydronic heat source. Expensive compared to a water heater, but cheap compared to a high-efficiency boiler in many cases.
A standard gas water heater may be good for only 70-75% net efficiency.
Another option is to run an indirect fired water heater that uses your boiler to heat the water e.g.
http://www.weil-mclain.com/netdocs/plusframes.htm
Pricier than a water heater but will last forever.