Tankless WH Questions - HVAC - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC


Thread Tools Display Modes
Old 02-16-2008, 07:04 AM   #1
Join Date: Dec 2006
Posts: 24
Rewards Points: 10

tankless WH questions

My NG tank WH is on its last legs and I am interested in going tankless. But I have a couple of possible issues.

First is that my 3 level townhome, with utility room on otherwise finished lower level presents limited venting options. The original WH is vented in the same type B stack as the NG furnace so that is not an option. My only option looks to be to take the Cat III stainless vent out the front side of my house on a piece of wall above my hose bib. It looks like a good place and meets all the required clearances except it I won't be able to maintain greater than 12" from an inside corner. It'll be more like 8", but it is brick. So irrespective of a possible code conflict is there any *practical* problem with this?

Second, the unit I am looking at is 199,000 btuh. My gas supply line is 1/2" diameter 2 psig to the manifold and regulator. The manifold is 1" iron pipe with 5 outlets to furnace, range, gas fireplace, gas grill, and tank water heater. Tank WH is 40,000, range/oven is 60,000, furnace is 80,000, gas grill is 40,000, gas fireplace is 30,000.

Is this gas supply likely sufficient to run the tankless WH and the furnace at the same time? I would run 10' of 3/4" supply line to the tankless.


homer12 is offline   Reply With Quote
Old 02-28-2008, 09:36 AM   #2
Chicago, IL
Michael Thomas's Avatar
Join Date: Jan 2008
Location: Chicago, IL
Posts: 1,037
Rewards Points: 500

1) On low pressure systems you may also have problems with the meter sizing.

2) Watch the clearances on the CAT III vent.

3) Unless this is a direct vent unit pulling it's combustion air from the exterior adding 200K BTUs may:

A) Exceed the available interior combustion air.

B) De-pressurize the structure, causing other appliances to back-draft.

C) Draw in additional exterior air, causing the interior humidity in cold months to be lower than you might prefer.

I've put up a page on these and other tankless water heater installation issues I have encountered on my own projects and at Home Inspections here in Chicago / Evanston


Last edited by Michael Thomas; 02-28-2008 at 09:46 AM.
Michael Thomas is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Adding a subpanel to a sub-panel and other questions CardinalPilot Electrical 14 03-30-2011 02:23 PM
Recommend Tankless Heater? DIYtestdummy Appliances 10 02-11-2008 08:26 AM
tiling questions - in middle of install mwill Flooring 8 12-11-2007 05:06 PM
Tankless hot water heater??? psychocandy Plumbing 1 03-22-2007 10:41 PM
Installing a tankless water heater ? bdalekid Plumbing 3 02-26-2007 07:26 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1