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Viessmann Vitocal AWHP for hydronic baseboards or retrofit floor heating?

Voodoo90
Voodoo90 Member Posts: 5
in Radiant Heating

Hello,

I hope I am in the right subcategory.

We are currently on hydronic baseboards with oil furnace. We will definitely be moving away from oil.

However, we do want to keep heating with a hydronic system for the various advantages it has compared to forced air heating. My wife has also made clear that for her forced air is not an option.

This brings me to the point where an air to water heat pump comes into play.

I have tried to read a lot about capabilities of that heat pump with baseboards, the efficiency in heating with a legacy hydronic system, but information is limited.

Do people have experience with running an AWHP with baseboards?

Is a floor or wall heating retrofit feasible and which system system would be advisable?

Regards

M

Comments

  • hot_rod
    hot_rod Member Posts: 25,918

    I would first do a heat-load for the home

    Make any energy upgrades, you can. The lower the heat load the better tir the hp and energy cost going forward Then determine how much fin tube you have. The actual fin, not just the enclosure

    Then use an output chart to see how the fin tube matches the heat load

    Dual fuel is a good option if the HP cannot make the load in the coldest periods

    https://www.caleffi.com/sites/default/files/media/external-file/Idronics_25_NA_Lowering%20water%20temperature%20in%20existing%20hydronic%20heating%20systems.pdf

    I have that exact HP in my shop. With radiant slabs I can run the system 115f or lower

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Voodoo90
    Voodoo90 Member Posts: 5

    I will get on it.

    We were wondering if retrofitting actual radiant heating in the walls or floors from underneath makes sense? Ideally we would have the main and first floor with radiant heating and leave the basement on baseboards, maybe a fan coil.

    It would obviously involve quite a bit of drywall work.

  • Jamie Hall
    Jamie Hall Member Posts: 26,515

    The advantage of retrofitting a lot of radiant heat into the floors or walls is that you can get away with running lower temperatures in the circulation. This is a definite factor when considering air to water heat pumps, as their maximum output temperature is much lower than the maximum temperature achievable with a boiler — at least with the present state of the art.

    The downside is obvious: you'd be gutting most of the house. This would be inconvenient (at best) and expensive.

    As @hot_rod said, the first three steps are improving the envelope as much as possible. Keep in mind while doing this, however, the minimum recommended air changes in a house to maintain indoor air quality.. Anyway, having done that, then determine the actual heat loss of the house. Then looking at the existing baseboard radiation and determine at what temperature it needs to run to satisfy that heat loss.

    Then you can start looking at what heat sources — including the air to water heat pump and mod/con boilers or a combination — will satisfy the requirements.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • psb75
    psb75 Member Posts: 1,071

    As Jamie mentioned, necessarily tightening up the house resulting in reduction of air change requires that you pay close attention to indoor air quality. This requires yet another expense for a mechanical system—an HRV or an ERV—that changes the air and recovers much of the heat in that process.

  • Kaos
    Kaos Member Posts: 758
    edited September 22

    First step is to figure out your starting point. How many liner feet of baseboard you have and how much oil did you burn through last winter. Winter energy used in Therms*42 is about your heat loss. For more accurate number run the math here:

    https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    AWHP likes to run at around 115F max, you can then see how much of the house heat your existing baseboards can supply at lower temp.

    From there, you need to add extra emitters to make up for the shortfall. The easiest is oversized low temperature panel rads to replace sections of baseboard and a bit of floor heat where easier to get to without major demo.

    Hot_water_fan
  • Voodoo90
    Voodoo90 Member Posts: 5

    Thank you for the input. I will get into finding out what our heat loss is soon and then work from there.

    I would be very much open to expanding the current system a little bit with a few rads or replacing some baseboards if thats enough.

    For the under floor heating…we would have to install a PEX system with aluminium heat plates on the subfloor from below. A very good friend is a carpenter and has offered to do/help with this, mostly taking care of the drywall demo and reinstall part.

    Our floor is solid wood throughout the house though. Is there a calculator or a way to find out if in floor heating in the main and upstairs floor would be enough to heat?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,828

    How much heat you can push up through the floor can be determined pretty easily. Floors have a max floor temp as well. But you need the heat loss first before working on that.

  • Voodoo90
    Voodoo90 Member Posts: 5
    edited September 25

    So we had an energy assessment done and the heating load of our house is 38000 BTU. The auditor said that insulation is up to date and there is nothing we can do that would not be invasive and economic.

    With that in mind I was looking at the sizing of the Viessmann Vitocal 100 AW which comes in a 34000 BTU or 58000 BTU size.

    What would be the way to go?

  • Kaos
    Kaos Member Posts: 758

    How does the fuel use calc compare to the assement? How many BTUs is your existing radiant capable of using 115F water?

    Generally with AWHP oversizing buys you a bit of extra efficiency as long as you are not short cycling it. Check the min output of the unit and make sure your smallest zone is above it or add a buffer tank.

    Since the install cost is so far removed from BOM cost, there is very little drawback in this case for the larger unit.

  • hot_rod
    hot_rod Member Posts: 25,918

    what temperature water do you require?

    The tech manual has good graphs for performance and efficiency at difference conditions

    IMG_1093.png

    https://www.viessmann-us.com/content/dam/public-brands/ca/pdfs/heat-pumps/vitocal_100-aw_am2v_tdm.pdf/_jcr_content/renditions/original./vitocal_100-aw_am2v_tdm.pdf

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Voodoo90
    Voodoo90 Member Posts: 5

    When I use an average of 30 BTU/sqft for the radiant heating system I would be able to output 60k BTU/hr. at around 100°F. But that is only for the main and first floor.

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