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Community and Q&A

What to heat with in small duplex development

MURRAY BANTING | Posted in Energy Efficiency and Durability on

Hello, I am in final design stages of a small development on Vancouver Island Canada. It is 13 duplexes consisting of 850 sq.ft each on one level on a heated crawl space. They will be very tightly sealed and insulated. I want to reduce electrical needs to site to a minimum. I have natural gas so plan to use it for heat, cook, dryer, hot water. I am thinking of using the Ranaii direct vent heaters for main heat and tankless hot water. I may need or want to add a small ERV for added air movement and exchange. Im not concerned with cooling at this point as will be electric and may offer homeowners a floor mounted portable for the few weeks they might need cooling and then can be put away for the rest of the time. Im looking for suggestions and ideas or experiences with anything similiar. I have concerns with heating the crawl and air movement in the crawl as well. one small baseboard heater may do down there with a duct from the ERV ? I am avoiding the mini split due to need for electricity but opinions welcome as the ERV will need power too. Thank you. Murray

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  1. GBA Editor
    Martin Holladay | | #1

    I'm assuming that you are a developer, not a heating engineer or hydronic heat contractor. If you really want to install hydronic heating systems that use gas-fired Rinnai tankless water heaters, I urge you to hire an experienced hydronic designer. Ask this person if he or she has successfully installed a heating system based on the Rinnai tankless you intend to use.

    These systems are often problematic. In many cases, the problems are solved by installing a tank-style heater as a buffer. This raises many questions -- especially, "Why go tankless if I need a tank?"

    Other potential problems concern the temperature of the return water and pump sizing issues.

    For more information, see Choosing HVAC Equipment for an Energy-Efficient Home.

  2. GBA Editor
    Martin Holladay | | #2

    Here is an article that may answer your questions concerning conditioned crawl spaces: Building an Unvented Crawl Space.

  3. Expert Member
    Dana Dorsett | | #3

    Without a heat load calculation it's hard to say if a tankless combi is the right approach, (and I expect that it isn't.) A code-min 850' duplex in that climate is likely to have a heat load under 10,000 BTU/hr, and could be half that depending on the definition of "...very tightly sealed and insulated."

    Designing low-output hydronic systems around a condensing tank HW heater is more forgiving & flexible. Using a condensing Polaris or HTP Phoenix Light Duty instead of a tankless would allow you to micro- zone the place without increased risk of short-cycling, and would have PLENTY of BTU output for your HW needs. Even a lower efficiency combi might be more appropriate than a Rinnai.

  4. Expert Member
    Dana Dorsett | | #4

    A few things to consider:

    The very smallest direct vented Rinnai cost about $750-800, and runs at ~82% efficiency.

    The smallest indoor Rinnai Tankless (which is NOT rated for space heating use) runs $650, plus whatever the venting kit runs- call it $1000 for hardware alone, no installation labor, also 82% efficiency.

    But since the tankless has a 150,000 BTU burner it requires bigger gas plumbing and possibly even a bigger gas METER to manage all burners. AND to use it for your crawlspace baseboard requires more hardware than it's probably worth for that alone. A tankless is also higher maintenance than a tank HW heater.

    A Bradford White CombiCor has about the same hardware cost, half the burner size, same AFUE performance as the low-end Rinnai solution, and is already set up with an internal heat exchanger for running space heating, making for "keep it simple stupid" hydronic heating systems possible even for the math-disinclined.

    The HTP Phoenix Light Duty costs a couple grand also half the burner size of the tankless, is set up for hydronic heating, but still needs an external heat exchanger & an extra pump, but it'll last ~2x as long as the CombiCor, and runs at substantially higher efficiency.

    But a heat load calculation is a must for figuring out how much radiation/baseboard you'd need in each room. Fin tube baseboard is fairly cheap stuff, and at 55-60C water temps will put out about 250-300 BTU/hour per running foot of baseboard. There is nicer radiation to be had (for quite a bit more money), but fin tube is not a bad way to go with high-mass heat sources like hot water heaters. If the total heat load is, say 10,000 BTU/hr you'll need about 40-50 feet, at a hardware cost of $10-12/foot, call it another $500 per duplex unit. If the load calc comes in around 7000-8000 BTU/hr (likely) it'll be proportionally less.

    Radiation & pumps included a CombiCor solution would come in under $3K in hardware in one-off pricing, and in a production build out of 26 identical systems even the installed cost might even be under $3000/unit.

  5. Aj Builder, Upstate NY Zone 6a | | #5

    I am contemplating a mod con right now... you need an experienced installer who carries parts and write up an agreement for two years worth of service and warranty on all parts and all service calls and all labor. Make sure he has access and carries all the spare parts. Might be worth stocking spare parts on site since you will have 13 units, it would be well worth it. You also need 24/7 service call availability. With the right company you will transfer these headaches appropriately and all will be happy.

    Too bad you can't go with mini splits as I think all electric with solar and super insulation is the best direction going forward for all parts of North America. Small units with gas stoves is not ideal.

  6. MURRAY BANTING | | #6

    Hello everyone who replied so far, All great advice, there may be some confusion however as I was only planning the tankless hot water for the actual hot water and not to heat home with. Electricity is super expensive and constantly rising here thus my urge to avoid it for long term. I will hire an expert to consult on whole home heat so for now trying to get ideas and educated on options out there for these small homes. The mini splits might be OK if I can go gas on the other main appliances but will need to see what loads will end up at. The baseboard heater I mentioned was just one to heat crawl space and avoid extra hardware to do that space but needs air flow too I assume. Some super small forced air gas furnace may end up being the solution for air flow and heat. Ive been told I would need less than 15ooo BTU system, I expect more like 10000 but just guessing so far. Heating always seems to get overkilled in small spaces and one little ceramic heater seems to heat the place in the end ? Still open for suggestions and thanks again ! Murray

  7. GBA Editor
    Martin Holladay | | #7

    Now that I understand that you were thinking of heating these units with gas-fired space heaters (the kind with through-the-wall venting) -- I'm one of the respondents who misunderstood -- I can say that your plan will work. Here is an article you might want to read: Heating a Tight, Well-Insulated House.

  8. John Semmelhack | | #8

    GBA is a great source for general advice to get you pointed in the right direction....however...(not trying to be rude)...with 26 units on the line, you really ought to be paying for professional consulting on this. I don't do work in your part of the world, but if this project was in Virginia, for example, it would be right up my alley. I regularly work with builders and owners on projects like this to optimize systems for comfort, dependability, low up-front cost and low operating cost. In some cases, my fees are completely absorbed by equipment/labor savings over what the owner or mechanical design/build contractor was originally intending. I'm sure there's someone in the Victoria/Vancouver/Seattle area who can do the same for you.

    A few words of general advice and a question -

    1) I don't know what the layout looks like, nor how good the building envelope will be, but point-source heating can be problematic for single-floor living....namely when bedrooms or bathrooms are too far away from the heat source and/or have "too high" heat loss.

    2) Is the crawlspace sealed and insulated...or is it vented?

    Good luck with the project!

  9. Expert Member
    Dana Dorsett | | #9

    The smallest gas hot air systems are going to be 2-3x oversized for your loads.

    Tiny output hydronic air-handlers that can use a tank-type HW heater as a heat source have been fairly popular in CA, but I don't have direct experience with that solution. But if the units are a single floor running ducts in the crawlspace (including some air-exchange in the crawlspace itself would be pretty cheap & easy. They usually come with an air conditioning coil included, but you don't have to use it. A 1.5-2 ton unit would be less than a grand, would deliver 10-15,000 BTU/hr using 55C water from a tank type hot water heater. If you go that route there are some design issues to attend to in order to avoid destructive condensation in the heat exchangers of a non-condensing hot water heater, but it's not rocket science.

    Some models that might work are the Comfort-Aire AHG24:

    ...or maybe the FirstCo 18HBQB :

    Rinnai, Ruud and Rheem make air handlers designed for use with a select models of tankless, but it's not clear they are a good fit at very low loads.

    The FirstCo units have oversized coils designed for high output at water-heater type water temps though ( rated at 140F incoming water), which may make them as oversized as a 30KBTU/hr gas furnace would be, and even the 18HBQB would require a bigger burner than a standard 40 gallon gas-fired tank (something north of 45,000 BTU/hr in) to avoid condensing issues, but that's not a huge cost-adder.

    I don't quite understand the requirement to actively heat rather than simply ventilate the insulated crawlspace with regular air exchanges with the living space, since the heat load of that space would be miniscule.

  10. Aj Builder, Upstate NY Zone 6a | | #10

    Wall heaters, one per unit?

  11. MURRAY BANTING | | #11

    Hi, More great advice/ideas//suggestion and I am new to this site so very impressed. I am one of those people who just cant accept the norm when I know there has got to be a better way. I now think that the hydronic air handler will be a good option to pursue as it moves the air and heats/cools it and deals with air movement in crawl as well. I too had concerns with air movement with the wall heaters thus thinking of need for an EVR but if the hydronic system running off hot water via gas may be a clear winner. Lots of articles for me to look at from the info provided. If anyone wants to contact me directly for further advice feel free via email or further posts here, my email is [email protected]

  12. Expert Member
    Malcolm Taylor | | #12

    Murray, Before going too far down any road you might want to look at the amendments to the BC Building Code that come into effect on Dec 19th. They deal with the need for mechanical ventilation to each bedroom and how crawlspaces must be heated and ventilated.

  13. Stephen E | | #13

    As with any rentals have the renter pay all utilities. Behavior play a huge role in being green. Renters will destroy you ROI without remorse if you pay the bills,

  14. Expert Member
    Malcolm Taylor | | #14

    Are they rentals?

  15. Charlie Sullivan | | #15


    Have you considered a single boiler or other hydronic system feeding the whole development? That opens lots of interesting options, such as clean and efficient wood-chip boilers and potentially even cogeneration (aka CHP, combined heat and power). Your development is pretty small compared to some "district heating" systems but it might still make sense.

  16. MURRAY BANTING | | #16

    Malcom, as of now planning for sales but rental may be an option depending on market etc. I am aware of some of the issues with building code changes but havent got the complete story yet, I am assuming ill need an ERV or something if I go with highly efficient heating such as hot water to radiator units etc. Code looks like its forcing people backwards rather than forwards as not considering small energy efficient homes in their equation. My favorite so far to heat with is a european style hot water appliance to feed radiators with low watt fans and DHW. Then may need a HRV or ERV like the Zehnder Confoair 160 to move air around. Problem is code will likely force me to use standard forced air to get air movement and heat for low initial cost but not what I want to do (40000 btu in a space needing 10000). I want to AVOID hydro wherever possible.

  17. Stephen E | | #17

    Given what codes are and what the heating requirements are... The simplist is a PTHP system. Provides outside air, provides heat pump operation to 25 degrees and backup heat below that. AC is included. I was reading a earlier response about putting the PTHP's in the closet's and piping it into the rooms. Takes care of noise issues and gives a more polished look of a central heating system. Haven't tried it myself, but it's within specs. I do use the 26" PTHP's in the rentals I have with great success. Have one unit that's not even using it to heat, just the first floor bedroom electric baseboard heater to heat the two story three bed two bath.

  18. Expert Member
    Dana Dorsett | | #18

    Whatever energy codes were in B.C. last week, they'll be different beginning a week from today:

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