High Efficiency Furnace Venting - DIY Chatroom

Mnrunner · 01-17-2009, 01:47 PM

I'm considering a new 95% high eff. furnace. I'm told I can not vent both my hot water heater and the 3" furnace vent up the original 6" furnace vent?? It will be costly to vent the furnace out the side. What are my options??

yuri · 01-17-2009, 02:38 PM

Why is it costly to vent it out the side wall? My co does it cheaper thru the wall than up the chimney. They cannot share the same chimney. Convert to an electric water tank and use the old chimney if necessary. If you have the $$ buy a tankless thru the wall water heater.

Dr Heat · 01-17-2009, 02:43 PM

Why a 95 it may well be that an 80 would be a more cost effective choice.

What is the fuel source LP or NA

How much pvc will be needed to run a new flue

Is the existing flue small enough to handle just the water heater or will you need to instal a liner for the water heater?

Where are you located?

yuri · 01-17-2009, 02:53 PM

That is correct. We have to downsize our liners to 4" to match the appliance/water heater and that costs extra. LOTS of people change to electric water heaters when going high efficiency and then cap off the old chimney.

pcampbell · 01-17-2009, 02:58 PM

Venting out the side should be very cheap and very easy. More details please!!!

Mnrunner · 01-18-2009, 06:06 PM

My basement is completely finished with the only option is to go to the front of the house. I'm told there will be too much steam and look bad.

I'm located in MN. I was hoping to vent a 95% eff furnace up the original 6" vent then also vent the hot water heater along side the new furnace vent (inside the 6" vent) It is a natural gas furnace and water heater.........

yuri · 01-18-2009, 06:18 PM

The code now says that a hot water heater needs a 4" B vent in a uninsulated brick chimney. This would be 5". Also the heat from a single wall 4" liner will damage 2"PVC and the code would not allow that anyway. Unless your electricity costs are very high I would convert to a electric water heater. Compromises have to be made sometimes. You would also have to terminate the water heater liner with a screen bird cap and the furnace venting would run into that so it is impossible.

Dr Heat · 01-18-2009, 07:49 PM

why 90% stick with the 80% use existing chimney
(that assumes the existing chimney is ok)

You will see only about a 6-7% difference in fuel usage. The cost of electric for the water heater + the additional cost of the furnace, will eat up any savings you will get.

yuri · 01-18-2009, 08:21 PM

With due respect, 6-7 % difference? I would be interested in some documented figures of that if you have. More like 10% or higher from my sources:http://www.hydro.mb.ca/your_home/hom...omparisons.pdf

**beenthere** · 01-18-2009, 09:23 PM

If your getting a 90% plus, make sure they pipe it up as a direct vent.

If its properly sized, its worth the savings.

Unless you own stock in the gas company.

Dr Heat · 01-18-2009, 10:04 PM

Quote:

Originally Posted by yuri

With due respect, 6-7 % difference? I would be interested in some documented figures of that if you have. More like 10% or higher from my sources:http://www.hydro.mb.ca/your_home/hom...omparisons.pdf

Perhaps I should be more specific: you will save 10% or more on your heating bill but not on your gas bill.

First you can only extract 80% of the BTU by burning NA to get more you need to explode it (Lennox puls) or vaporize (the old Amana) So if you whant to figure a dollar savings you need to take 20% off the top This is fuel that you will lose regardless of afue

Secound the furnace is not the only gas appliance to be conciderd
Water Heater Oven cook top dryer pool heater etc.

So, what I am saying is for a 6% to 7% savings it may not be worth all the extra up front expence

Dr Heat · 01-18-2009, 10:07 PM

Quote:

Originally Posted by beenthere

If your getting a 90% plus, make sure they pipe it up as a direct vent.

If its properly sized, its worth the savings.

Unless you own stock in the gas company.

If you have combustion air in the mechanical room does a two pipe really increase efficiency by that much

hvaclover · 01-18-2009, 10:26 PM

Quote:

Originally Posted by Dr Heat

why 90% stick with the 80% use existing chimney
(that assumes the existing chimney is ok)

You will see only about a 6-7% difference in fuel usage. The cost of electric for the water heater + the additional cost of the furnace, will eat up any savings you will get.

The "Ol Farmer's been hitting the home grown.