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Energy efficient placement of mechanical room

Sal_123 | Posted in Energy Efficiency and Durability on

Building a home in the Northeast, as I’m looking over the basement layout and options where to position the mechanicals – hot water heater – given the house design, from corner to corner on a diagonal, it is close to 150′. On one far end, the master bath and bedrooms on the second floor, on the opposite main floor, the kitchen, everyday living space and likely most used bathroom. So my concern is to get hot water to the faucet, from either of the two opposite ends, will require running the hot water for a period of time until all the cold water in the plumbing is flushed and it is filled with hot water which then will sit and cool, wasting energy, only to repeat the process with any demand of hot water. Have spoken to a few plumbers, use of instant hot for the area less utilized, circulating pumps, maximizing insulation of the tubing system, are the suggestions I have gotten. Was considering two mid sized water heaters in opposite locations rather than one centrally located main hot water heater. One said OK “whatever you say”, the other two didn’t seem to appreciate my concern for such minutiae. Is my concern unrealistic? Any constructive input/ideas are greatly appreciated.

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  1. Dana1 | | #1

    What are you using for space heating?

    " ...the Northeast..." has a very broad geographical definition covering US climate zones 4A through 7A. Can you narrow that down a bit (say, with a ZIP code)?

  2. Sal_123 | | #2

    Of course, zone 5A. No definitive choices yet, Looking at first floor radiant under tile with mud floor for thermal mass, second floor baseboard. Pricing outdoor wood boilers systems and and their feasibility. Considering any design and/or combination that makes sense. House is 5200sq ft.

  3. charlie_sullivan | | #3

    Obviously the ideal would be reconfiguring the whole floorplan to cluster the hot water uses closer together. Short of that, I'd lean towards putting the water heater closer to the kitchen and that bathroom, assuming that gets more frequent use through the day.

    Even if you special-order 1" thick pipe insulation, it won't keep the water warm more than a few hours, so for infrequent use you are throwing away the full pipe volume of hot water each time you stop using it. So for infrequent use locations, making sure the pipe is no bigger diameter than it needs to be saves more than making the insulation thicker.

    Continuous circulation only wastes energy, but on-demand circulation pumps can save a little energy vs. dumping lukewarm water down the drain, and they also save significant water if that matters in your location.

    For a location that is primarily handwashing, a small local demand heater is a great solution. But with dishwashing at one end of the house and showers at the other, you have larger hot water uses in both places.

    Without a great solution to efficient distribution, you can still use other best practices for hot water:
    1) A heat-pump water heater.
    2) A "powerpipe" drain water heat recovery system. This works best for showers, and so it should be located near the showers.

  4. user-2890856 | | #4

    Where in 5A are you Sal ? Is this a job that was designed first by an architect without consultation with contractors ? Sounds like it .

  5. GBA Editor
    Martin Holladay | | #5

    Don't install an outdoor wood boiler. They are polluting and inefficient.

    It's a shame that this large house was not designed to cluster the hot water uses near each other. If you are wedded to this design, the solution is to put your main water heater on the side of the house with most of the uses, and a tankless water heater (either gas-fired tankless or electric) on the other side of the house.

  6. Expert Member
    Dana Dorsett | | #6

    +1 on the "friends don't let friends install wood boilers" front. The only way to get the full efficiency out of an outdoor wood boiler and minimize the huge emissions problem is to install them with a large thermal buffer tank and always run at max fire until it it self-extinguishes.

    By the time you've engineered and installed the insulating buffer tank & controls you'd be in the cost range of a higher efficiency low emissions pellet boiler with smart controls that could live indoors (OkoFen, et al). Many of those have domestic hot water options, which would make the pellet boiler a reasonable approach as your main hot water heater.

    An electric tankless is an underpowered potential liability if/when residential customers are hit with "demand charges" to pay for the grid infrastructure needed to support their peak loads. From a cost point of view a pair of heat pump water heaters sized for the biggest tub it each has to fill makes more financial sense (assuming you aren't on a natural gas main), and won't require adding an additional 100A/240V to the electrical service per electric tankless. An electric tankless is really not worth it when you consider the installed cost of what it takes to get even mediocre hot water performance at your mid-winter incoming water temps, even if you are never hit with rate structures that apply demand charges. A heat pump water heater (or two) would also noticeably reduce the run time of your basement dehumidifier. Mechanical dehumidification of the basement is usually necessary in summer, since the deep soil temperatures are well below the average outdoor dew point temperatures in your area.

    If showering is more popular than tubbies at your house, a drainwater heat recovery heat exchanger (Charlie Sullivan's "powerpipe" recommendation) downstream of the main shower feeding both the cold feed of the hot water heater on that end and the cold water side of the shower dramatically improves the "apparent capacity" of the tank in showering mode, as well as the efficiency. It does nothing for tub-fills though, since the heat has to be extracted from the water flowing down the drain and applied to the water feeding the shower & tank. The biggest one (both diameter and length) that fits gives the highest heat recovery efficiency. If you buy wholesale from EFI (easy to set up an account over the phone), for about $600 you can get one big enough (a 4" x 48" or 3" x 60" or bigger) for better than 50% energy return, which can be enough to mean the difference between a 50 gallon heat pump water heater and an 80 gallon for supporting multiple back-to-back showers, sometimes paying for itself in reduced water heater cost even before counting the efficiency.

  7. Sal_123 | | #7

    Wood is abundant, given I continue to cut, split and season it. A wood burning stove on the first floor and a pellet stove in the basement (for as needed use and eliminates the mess and effort of wood transport to the lower level) are part of the plans. Unfortunately the design is typical, not many neurons challenged in the initial planning phase in regards to efficiency. No contractors were consulted in the design. I recall asking the architect his thoughts on ICF and he looked at me with a blank stare. Typical in my neck of suburbia, but ever so slowly changing. The framer is perplexed as to why anyone would ever spend the money or make the effort to apply exterior rigid 2.5" XPS insulation. I feel obliged to make “outie” windows out of fear the “innies” (which boasts wall thickness, albeit isn’t all that) would be too demanding on the guys flashing the windows. So local contractor support is close to nil.
    Yes, natural gas is available. It seems the answer is putting the main water heater on the side of the most use, bedrooms, and a gas-fired tankless on the opposite side, albeit it is the kitchen side. My gestalt is showering wins that fight.
    So outdoor wood boilers “bad”. In their defense, Dana, was looking at a Garn, firing it with “perfectly” seasoned wood every other day in the deep of winter and using its massive water reservoir as a thermal buffer. I will look into your suggestion of a higher efficiency low emissions pellet boiler with smart controls that could live indoors. Given wood is plentiful, had not entertained such an option, but remain skeptical as I have to buy pellets.
    Hopefully no need to dehumidify the basement. Planning to use 1.5” inch XPS and 15 mil Stego in the subslab space and exterior rigid XPS on top of the foundation walls. Using a brush-on bituminous based capillary break between footings and walls. Looking forward to celebrating the day I no longer hear a dehumidifier running 24/7 in the basement.
    Thanks guys

  8. Expert Member
    Dana Dorsett | | #8

    The self buffered Garn is not the typical outdoor wood boiler of un-neighborly lawsuits all over New England. Unlike most others it can also be installed INDOORS, which means the standby & distribution losses accrue to the conditioned space rather than being wasted. They are designed to be loaded and burned to self-extinquishing rather than crudely temperature limited as with many outdoor wood boilers. If you're going that route Garn is about as good as it gets, and they have fairly decent PM2.5 numbers compared to most wood-burners.

    There's almost no case to be made for a gas-fired tankless compared to a condensing tank type HW heater that takes less maintenance (especially if you have any hard water issues.) A gas fired tankless may makes sense if space is at a premium, but something tells me that in a 5200' house there's enough room to take on both a Garn and a couple of tank type HW heaters. (Getting a Garn Jr. into the basement could be an issue though- i'ts not as if you can take it down the stairs. :-) )

    If you don't have any monster-tubs to fill any power-vented Energy Star gas fired tank is going to be fine, and if installed in combination with a drainwater heat recovery heat exchanger will nearly deliver the "endless shower" experience (unless it's some ridiculous luxury master-suite shower with multiple 2gpm side sprays or something) capable of 3-4 successive showers back-to-back. That endless shower thing is a bit of a problem with some folks (take my kid, for instance :-) ), so it may require installing a vacancy detector light switch in the bathroom to time out at 10 or 15 minutes (or whatever you find works for you) after the last motion was detected, as a hint as to when it's time to get out. (That worked for us. YMMV.)

  9. Sal_123 | | #9

    That's genius, A vacancy detector light switch, 15 minutes or your in the dark ; )
    Was considering lowering the Garn into the basement by crane before installing the main deck. The idea of firing the unit in my pajamas at the end of the day swirling a Scotch sounds great. But the reality of wood - transporting it, the mess, pests etc.- is daunting. Had considered "loading chutes" in the foundation wall to drop in a load, akin to the old coal delivery chutes, or a drive down ramp to haul quad trailer loads of wood in at a time, but don't think so. The mess is eternal. A Garn shack next to the garage is a cleaner alternative, despite some environmental losses. The costs to set the thing up in combination with the purchase cost are significant, have to do a cost analysis over years to estimate the time it pays itself off, may not be around by then, LOL!!

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