Heating

Indirect Water Heater Sizing

Hello, I currently have two 40GL gas fired water heater. I want to install an indirect water heater instead. It is going to work with standard efficiency boiler (Burnham Series 2). The hause is 2 family with 2 bathtubs, 3 showers, 1 dishwasher, 2 kitchens, 1 washer. What size of the tank for Indirect DHW…

by vkazman
09/01/2010

Hello,
I currently have two 40GL gas fired water heater. I want to install an indirect water heater instead. It is going to work with standard efficiency boiler (Burnham Series 2). The hause is 2 family with 2 bathtubs, 3 showers, 1 dishwasher, 2 kitchens, 1 washer. What size of the tank for Indirect DHW I should get? Do I have to use expansion tank with this system? If I want to have Hot water priority, what would be the cost for a controller that implement HW priority?
Thank you
Vad

Heating

Comments

  1. Interesting solution with the storage tank. Does it decrease efficiency of the system? I still will be able to use an expansion tank (for security)
    Regarding 56K BTU. My house is pretty small – 1700sft + 850sft basement. It has a stucco siding with at least 1” insulation. Taking in consideration that stucco was done on top of old frame. I considered wall insulation as R10 You still think that 56K BTU is too little?

    Thank you,
    Regards,
    Vad

  2. 56K BTUs to heat a 2 family in Brooklyn? Hmm.
    If that’s accurate, then your hot water demand is likely to exceed your space heating demand. You’ll have to size for the larger load if using a single boiler to do both jobs. If that leaves you with a terribly oversized boiler, then consider using a boiler sized for the heating demand and an insulated storage tank in addition to the indirect water heater if you find you’re lacking hot water later.
    You already know the heat exchanger can only transfer a limited amount of energy effectively, but you can add storage to the equation without increasing the coil size.

    Boiler heats the indirect water heater, the storage tank holds additional volume, a shuttle pump and tank thermostat tie it all in together.

  3. Thank you again, Master

    I did a heat loss calculation for my house and it is about 56K BTUs. Even if I choose 45 Gl Indirect, It is required 130K. Does it mean that I have to install the boiler that is about double size of my heating requirements? May be I am missing something but from my (unprofessional) point of view this installation is not going to be efficient.
    What is your opinion on it? Maybe for me more efficient will be to install regular gas water heaters even though they are not really efficient?

    I appreciate your help,
    Regards,
    Vad

  4. The obvious question is if you’ve done all the calculations and cross-referenced the literature, what help are you asking for? Sounds like you’ve got it covered.

    Why do you have 2 x 40-gallon water heaters now? Did one 40-gallon unit not cover the demand, leading to the addition of a second one? You’ve got 80 gallons in storage and probably 80,000 BTUs.

    I would consider it a major failure in design if I spent the money it takes to install an indirect water heater, only to find myself installing an electric water heater to supplement it.

    I’ve seen the frustrating results of an undersized hot water heating system and I strongly advise you to reconsider going with a 30-gallon.
    45 gallons with a 130,000 BTU boiler is probably pretty safe, but make sure you’ve got those numbers right.
    I like the HTP tank for it’s warranty, availability and customer service. But depending on the boiler, especially very high-efficiency units, the tank-in-tank designs are often a better choice.

  5. Hello Master, Thank you for reply

    60Gl sounds huge it requires almost 200K BTU. My boiler will be maximum 130K BTU (maybe less)
    I am thinking that 30 or 45 can be maximum since it can provide 212GL in the first hour it will be much more than enough to fill 2 bath tubes (~100Gl for two). 8-10Gl Flow Rate is enough especially if to use low flow shower heads. There will be only 1 dishwasher and 1 washer in the house.
    I was reading that smaller size works more efficiently. I am thinking if I under-size it is always possible to install a dedicated electrical water heater let say for dishwasher or washer. Are you disagree?
    What happens if Indirect require more BTU than the boiler can produce. Is it a big problem?
    Why you think that HTP brand is better than others?

    Thank you
    Vad

  6. I use outdoor reset all the time with Series 2 and 3 boilers. No quick answer regarding sizing as it has more to do with recovery than storage, which is different when comparing coil-in-tank vs. tank-in-tank designs.
    I would install a 60 gallon SuperStor in a 2-family with a domestic water expansion tank.
    No downside to installing an expansion tank, ever. It takes a lot of expansion stresses off your system components.

  7. Thank you, I was thinking about it as well. Will it work with Burnham Series 2 boiler?
    Can somebody answer about sizing of Indirect WH and expansion tank?

    Regards,
    Vad

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