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  1. #1
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    Mar 2007
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    Western Montana
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    Default Water Heaters used for DHW and space heating

    I've seen standard gas water heaters used for space heating before (radiant floor heat), but never used at the same time for both hot water heat and domestic hot water. Assumed it would not be allowed. Surprised to see that under some condition, you can.

    Don't have details yet, but it seems to be two gas water heaters (2-story house), probably 75 gal each, 60,000 BTUs.

    I would be concerned about concern: water stagnation, bacteria, cross contamination, operating temperatures, need for sterilization vs. scald risks.

    Am I missing something? The biggest catch is that the manufacturer has to intended the device for the function. Otherwise, with use of anti-backflow valve, it seems to be allowed.

    What are the concerns?????

    What I see in IRC is:
    Ch 20 BOILERS AND WATER HEATERS
    WATER HEATERS USED FOR SPACE HEATING
    M2004.1 General. Water heaters used to supply both potable
    hot water and hot water for space heating shall be installed in
    accordance with this chapter, Chapter 24, Chapter 28 and the
    manufacturer's installation instructions.

    Ch 28 WATER HEATERS
    WATER HEATERS USED FOR SPACE HEATING
    P2802.1 Protection ofpotable water. Piping and components
    connected to a water heater for space heating applications shall
    be suitable for use with potable water in accordance with
    Chapter 29.

    Ch 29 WATER SUPPLY AND DISTRIBUTION
    P2902.1 General. A potable water supply system shall be
    designed and installed as to prevent contamination from
    nonpotable liquids, solids or gases being introduced into the
    potable water supply.

    P2902.3.3 Backflow preventer
    P2903.4.2 Backflow prevention device or check valve.
    P2903.4 Thermal expansion control.

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  2. #2
    Join Date
    Feb 2008
    Location
    Caledon, Ontario
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    Default Re: Water Heaters used for DHW and space heating

    I think you have a hand on the concerns.

    This diagram is indicative of how combinations systems are most likely/should be installed.
    Note the check valve and tempering valve.

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  3. #3
    Stephen G's Avatar
    Stephen G Guest

    Default Re: Water Heaters used for DHW and space heating

    [ATTACH]24723

    They seem to like combination units here. I just inspected one for a approx 1200sq ft home. It only had one gas unit, and it gets pretty cold here as well

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  4. #4
    Join Date
    Mar 2007
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    Spring Hill (Nashville), TN
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    Default Re: Water Heaters used for DHW and space heating

    Quote Originally Posted by Terry Beck View Post
    I've seen standard gas water heaters used for space heating before (radiant floor heat), but never used at the same time for both hot water heat and domestic hot water. Assumed it would not be allowed. Surprised to see that under some condition, you can.

    Don't have details yet, but it seems to be two gas water heaters (2-story house), probably 75 gal each, 60,000 BTUs.

    I would be concerned about concern: water stagnation, bacteria, cross contamination, operating temperatures, need for sterilization vs. scald risks.

    Am I missing something? The biggest catch is that the manufacturer has to intended the device for the function. Otherwise, with use of anti-backflow valve, it seems to be allowed.

    What are the concerns?????
    Apollo has been making dual systems like you are posting about for years and years. I see them from time to time and most of the time with very few problems.

    The water just flows through the system like normal plumbing lines, it does not just sit in the heater core of the unit. Cross contamination is not really an issue, it is really no different than a water heater system without the heater part. The water in a HW tank is not sterile anyway so I would not worry about that

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  5. #5
    Join Date
    Mar 2007
    Location
    New Mexico
    Posts
    1,258

    Default Re: Water Heaters used for DHW and space heating

    I just ran into this situation this past winter and posted on here about it. I couldn't find anything that would not allow it.

    Jim Robinson
    New Mexico, USA

  6. #6
    Join Date
    Mar 2007
    Location
    Western Montana
    Posts
    261

    Default Re: Water Heaters used for DHW and space heating

    Thanks for the info guys. The plumbing diagram was very helpful. I hadn't thought about a tempering valve; the system I saw today certainly need to add one. Guess I am more used to traditional boiler setups, pressure & temp gauges, expansion tanks, multiple pressure relief valves, one-way valve for make-up water, etc.

    I respect your answers, and it seems to be allowed in code, but it still doesn't seem right to me. In this case, there are two 50-gal gas water heaters running at 60,000 BTU/hr maintaining a 145-150 temperature all year round for heat that is only used to various amounts for 6-8 months at most. [This is a 2000 sq ft 2-story, 3 BD, 2-1/2 BA home with vented crawlspace built in 2000.]

    Scott, I guess I get what you said
    Cross contamination is not really an issue, it is really no different than a water heater system without the heater part.
    but for example there is this article at Apollo Hydroswirl Hot Water Tank replacement. | calgaryhydronicssolutions

    I have seen more than one thread that list concerns about stagnant water in a dual-use system below 170 degrees or so.

    Also, while cheaper than a traditional boiler, gas hot water heaters don't usually have anywhere near the lifespan of a most boilers I have seen. And some new boilers are incredibly efficient.

    Tried, but couldn't find install instructions from either Rheem (the water heaters installed in the house), or on the Apollo mixed use systems. If someone has install instructions it sure would be nice to see them.

    Thanks


  7. #7
    Join Date
    Feb 2008
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    Caledon, Ontario
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    Default Re: Water Heaters used for DHW and space heating

    Up here in Ontario it is now required to have the minimum water temp at 140F (Legionaires disease) and a mixing valve installed whether the HW tank is used for a combi heat system or not.


  8. #8
    Terry Sandmeier's Avatar
    Terry Sandmeier Guest

    Default Re: Water Heaters used for DHW and space heating

    As a former installer and tech, the mind set for these type of systems is cheap, fast, and less work. It works in some cases as used with a forced air unit, with baseboard or radiant system when greater volume of water is being used there could be deficiencies with the system. The better installations of this type usually have an external heat exchanger and keep a closed system for heating. Their are alot of factors to make this system efficient and durable. The biggest factor is heat temps needed for space heating 140+ in colder climates and tempering the water down to 125 for domestic use. Technically (Codes) acceptable for this type of installation but as a design stand point it leaves some wanting.


  9. #9
    Join Date
    Jul 2008
    Location
    Utah
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    389

    Default Re: Water Heaters used for DHW and space heating

    When I was a youngster which was not that long ago,( ) I put an in-floor radiant system in my master bath using the water from the water heater. Of course I had to use an all bronze pump for the circulator.

    A couple of issues I discovered:
    • The water temp was way too hot for the floor system. Until I turned it down there were spots on the floor that were actually very uncomfortable on my feet.
    • During the winter start up after the pump had been off all summer, the hot water in the shower had a very sliming smell from the stagnation in the tubing.
    While I was quite proud of myself for being so clever (so I thought at the time) I would never do it that way again because of those issues.


  10. #10
    Join Date
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    Caledon, Ontario
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    Default Re: Water Heaters used for DHW and space heating

    That's why a mixing valve is required in order to bring down the temp of water going through the tubing. But then again you likely know that now.


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