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Replace Forced Air Furnace with Hydronic Air Handler

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Eweneek1
Eweneek1 Member Posts: 4
Will be replacing my 80,000 BTU forced air unit next year and considering a hydro air handler. Already have a Rinnai 199000 tankless unit for hot water, but not installed yet. Had heating calculations done and need 70,000 BTU with 1000 to 1200 cfm for heat only for 1800 square feet.. Do not need A/C. Return air has a 14” duct and supply has two 12” main ducts plus about 12 6” supply duct branches. Would like to use existing duct work and only change supply and return duct sizes. Do I need a different tankless unit plus the hydronic handler? What else might be needed? All present equipment in crawlspace with a 5' height.

Will the air handler be quieter than my current 20 year Payne forced air unit?

Comments

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,897
    edited October 2022
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    I'd back up first -
    1. How was that heat loss calculated? It seems extremely high. What type of building is this? How is it being used?
    2. Was the existing furnace able to maintain setpoint? If it was 80kbtu input, it was probably smaller than your calculated heat loss, so upsizing seems unnecessary if it could maintain setpoint.
    3.
    Do I need a different tankless unit plus the hydronic handler?
    Ideally you'd use a boiler. If not, you could use the existing tankless domestic hot water heater but you might run into capacity issues. It depends on your hot water usage. It'll
    4.
    Will the air handler be quieter than my current 20 year Payne forced air unit?
    It depends. In my opinion, this is the crux here - why replace a furnace with an hydronic air handler and not just another furnace? You can use a modulating, high efficiency furnace just as easily (frankly probably easier) than adding a hydronic air handler with a new boiler. There's not much of an advantage using hydro-air, which is one of the reasons nearly no one uses it. You'd be basically mixing and matching different parts and brands and the best case scenario would be matching a furnace. It's more work with no reward.
  • pedmec
    pedmec Member Posts: 994
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    putting a hot water based system in a crawl space is not a good idea unless everything heavily insulated or your heating the crawl space. probably why they used a furnace in the first place.

    you can get a furnace with an ecm blower motor. really nice and quiet as long as the furnace is properly sized to the ductwork. if not that blower motor will ramp up to meet the cfm settings then it becomes noisy.
    GGross
  • bburd
    bburd Member Posts: 925
    edited October 2022
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    Agreed, another furnace makes much more sense. Hydro air is essentially a more complicated and costly way to duplicate what a furnace does. It makes sense in certain circumstances, like systems with multiple zones, but a single zone hot air heating system with no existing boiler is not one of them. Especially if it will be installed in a crawlspace were a cold weather power failure could cause frozen pipes and extensive damage.

    And if you want the new system to be quieter than the old one, discuss this with your contractor. There are ways to do it, although you’re likely to have to spend a bit more money.

    Bburd
  • Eweneek1
    Eweneek1 Member Posts: 4
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    Thanks for the comments. My first consideration was a Rudd U96V or Rheem R96V two stage variable speed multi-position furnace. Then, as I already have the Rinnai RU199IN tankless unit mounted in the crawl space only about 10 feet from the existing furnace why not go the hydronic route which might be cheaper to install. Didn't think a heat pump would be necessary. The Rinnai hydronic air handler output is 60,000 BTU and the Rheem is 80,000 BTU.

    Our home is a 1896 Victorian located in Eureka California. We have original single pane windows and 10 foot ceilings. Outside temperature ranges from 35 to 75 degrees during the year. I insulated our home with Bonded Logic UltraTouch™ Denim Insulation. Current heater has no problem maintaining a constant 67 degrees. It is a Payne unit installed in 1995. Last year I replaced and rerouted all the metal 30 gauge duct work with 26 gauge. I have kept it running myself. Time for a replacement.

    The furnace noise is primarily with the return air. After discussion with Savoy Engineering who prepared the Manual J load calculations, I increased the size of the returns from 10" and 14" to both now 14". No change in the return air noise.
  • bburd
    bburd Member Posts: 925
    edited October 2022
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    Most on this forum would agree that an appliance designed as a water heater does not work well for space heating, though the impulse to save installation cost is understandable. Standard or “Combi” boilers are designed for that purpose, but cost more than water heaters, and of course your water heater is already there.

    Return airflow noise is generally a combination of airflow velocity noise and fan noise.

    The velocity noise can be controlled by using larger return air grilles to reduce the airspeed at the grille faces, and larger ductwork.

    The fan noise can be controlled by inserting a sound trap, generally several turns in the return ductwork between the fan and the grilles. Acoustically lined ductwork can be part of the solution, but turns and distance are still needed. The worst situation for fan noise is a “furnace platform” with no return duct work, or a short return duct with no turns. These are very common in less expensive construction.

    Running the furnace fan at a lower speed also reduces both types of noise, which is the advantage of two speed or variable speed fans. Higher speeds are only needed in very cold weather or when recovering from setback.

    Bburd
  • pecmsg
    pecmsg Member Posts: 4,909
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    Eweneek1 said:

    Thanks for the comments. My first consideration was a Rudd U96V or Rheem R96V two stage variable speed multi-position furnace. Then, as I already have the Rinnai RU199IN tankless unit mounted in the crawl space only about 10 feet from the existing furnace why not go the hydronic route which might be cheaper to install. Didn't think a heat pump would be necessary. The Rinnai hydronic air handler output is 60,000 BTU and the Rheem is 80,000 BTU.

    Our home is a 1896 Victorian located in Eureka California. We have original single pane windows and 10 foot ceilings. Outside temperature ranges from 35 to 75 degrees during the year. I insulated our home with Bonded Logic UltraTouch™ Denim Insulation. Current heater has no problem maintaining a constant 67 degrees. It is a Payne unit installed in 1995. Last year I replaced and rerouted all the metal 30 gauge duct work with 26 gauge. I have kept it running myself. Time for a replacement.

    The furnace noise is primarily with the return air. After discussion with Savoy Engineering who prepared the Manual J load calculations, I increased the size of the returns from 10" and 14" to both now 14". No change in the return air noise.

    With that temperature range a heat pump is all that's needed!
    JakeCKGGross
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,897
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    I just can’t imagine a 1800 sqft house in this climate having a heat loss of 70,000 btu. When it’s “cold”, does the furnace run nonstop for hours at a time? If your heat loss is 70kbtu and your existing furnace is smaller than that (80,000 x 80% efficiency), it should be running nonstop. Or the heat loss is junk. 
    GGross
  • pedmec
    pedmec Member Posts: 994
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    I believe the numbers. That place is warm in December compared to where i live. He also is keeping it at 67 degrees and happy. now whether he can get it to 75 might be a different story.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited October 2022
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    You do not want to use a water heater for space heating. Water heaters are not designed to work well on a closed system like you are proposing. Water heaters use flow switches to turn on the burner. Unless you use an oversized circulator pump (which will be noisy) you may find that the burners will not light when the normal closed loop circulator pump size starts to circulate the water.

    1. A boiler will have a switch that is operated by a thermostat that will operate both the pump and the burner.
    With your idea, the thermostat will turn on a pump and hopefully be powerful enough to activate the flow switch.

    2. A boiler will operate just fine with 130° return water from the radiators or fan coils.
    A water heater will not work very well with 130° return water. it is designed to heat up 40° or 50° inlet water to 120° or 130° for taking a shower.

    3. You don't want to drink or cook with or even shower with the water that is in that fan coil sitting there all summer getting stagnant and perhaps growing microorganisms

    Maybe you want to look at a separate boiler for the fan coil + the air handler + the ductwork and necessary adaptors to fit the old furnace location + the water piping and auto feed and circulator pump and the low water cut off and the air scoop and the back flow preventer and the purge valves and the... I could go on and on.

    OR you can get another furnace

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,897
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    I believe the numbers. That place is warm in December compared to where i live. He also is keeping it at 67 degrees and happy. now whether he can get it to 75 might be a different story.
    It’s warm for sure! I think it’s worth a second glance and worth checking to see if the fuel usage matches up with a 70kbtu heat loss. I think this particularly because the air flow is causing noise issues - if @Eweneek1 only needs 300-600cfm, the system will be much quieter than 1000-1200. 
  • JakeCK
    JakeCK Member Posts: 1,401
    edited October 2022
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    There is no way he needs 70k btuh, not a got damn chance. What's he trying to do, heat it to 100f+ in January?...

    My house is 1500sq ft with almost no insulation and a design temp of 7f. I can heat it with 20k btuh less then what he's specing out.
    KC_Jones
  • TAG
    TAG Member Posts: 755
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    I had a project with hydro air (two units up/down) ..... IMO -- problem is control. In my case the system was designed to send 180 degree water to the air handler heat exchangers and turn on the fan .... one setting on/off. Later I tried to do a bit of outdoor reset so the water going to the exchangers better matched the need based on the outside temp. Unfortunately, was not able to automatically adjust the fan to a lower speed -- to better match the output. We could do two furnace in that project for various reasons. With all the modulating products available to day can't see how hydro makes any sense. Don't you have to do Heat Pumps in CA as well?
  • ChrisJ
    ChrisJ Member Posts: 15,852
    edited October 2022
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    In 1600sqft I use roughly 72,000 btu/h at -8F. 71-72F indoor temp. That's negative 8 degrees F.

    That's with very little insulation in some places, no insulation in others, no sheathing, just clap board siding with aluminum over it. 24 150 year old windows with some of the worst storm windows I've ever seen, but they're there.


    This is real world usage, not a heatloss calculation.
    I guess I could look and see what I use when it's 30F out but it's hardly worth talking about.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Eweneek1
    Eweneek1 Member Posts: 4
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    A little more information is as follows. Checked with Payne and my current heater is 115,000 BTU unit running at supposedly 80%. Today the outside temperature is 50 degrees. Lyric thermostat set at 67 degrees. Heater runs 9 to 10 minutes, then shuts off for 15 to 20 minutes. Don't know if inside humidity has any bearing, but usually around 80%.

    Second floor of home currently has no heat and is about 1600 square feet with 9 foot ceilings and insulated same as first floor. Will install a separate undetermined heat source.

    Reviewed California Building HVAC Requirements and they seem to be pretty lax.

    Discussion indicates standard 96% two stage furnace, electronic filter, and a dehumidifier. Heat pump might be cheaper to operate, but at a more substantial cost.
  • ChrisJ
    ChrisJ Member Posts: 15,852
    edited October 2022
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    Eweneek1 said:

    A little more information is as follows. Checked with Payne and my current heater is 115,000 BTU unit running at supposedly 80%. Today the outside temperature is 50 degrees. Lyric thermostat set at 67 degrees. Heater runs 9 to 10 minutes, then shuts off for 15 to 20 minutes. Don't know if inside humidity has any bearing, but usually around 80%.

    Second floor of home currently has no heat and is about 1600 square feet with 9 foot ceilings and insulated same as first floor. Will install a separate undetermined heat source.

    Reviewed California Building HVAC Requirements and they seem to be pretty lax.

    Discussion indicates standard 96% two stage furnace, electronic filter, and a dehumidifier. Heat pump might be cheaper to operate, but at a more substantial cost.


    Your indoor humidity is 80%?!?!
    That's an issue in my book.

    I don't like over 50% and over 60% is uncomfortable. I'm pretty sure 80% would pose a lot of health risks if it's all the time.

    A properly sized heating system will run non-stop on the coldest days of the year, and many will even say the indoor temperature should drop a degree or two during extremes.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,897
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    What is your annual gas usage? 96% seems like overkill and a heat pump shouldn’t be significantly more expensive than a furnace. 
  • JakeCK
    JakeCK Member Posts: 1,401
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    ChrisJ said:
    A little more information is as follows. Checked with Payne and my current heater is 115,000 BTU unit running at supposedly 80%. Today the outside temperature is 50 degrees. Lyric thermostat set at 67 degrees. Heater runs 9 to 10 minutes, then shuts off for 15 to 20 minutes. Don't know if inside humidity has any bearing, but usually around 80%. Second floor of home currently has no heat and is about 1600 square feet with 9 foot ceilings and insulated same as first floor. Will install a separate undetermined heat source. Reviewed California Building HVAC Requirements and they seem to be pretty lax. Discussion indicates standard 96% two stage furnace, electronic filter, and a dehumidifier. Heat pump might be cheaper to operate, but at a more substantial cost.
    Your indoor humidity is 80%?!?! That's an issue in my book. I don't like over 50% and over 60% is uncomfortable. I'm pretty sure 80% would pose a lot of health risks if it's all the time. A properly sized heating system will run non-stop on the coldest days of the year, and many will even say the indoor temperature should drop a degree or two during extremes.
    Maybe he's trying to kill the mold with heat. Would explain why he needs 70k btu in his climate. Lol
  • ChrisJ
    ChrisJ Member Posts: 15,852
    edited October 2022
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    18,000 btu at 50f outside.
    Actual is a little less than that but it's very very close in my drafty 150+ year old house.



    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • JakeCK
    JakeCK Member Posts: 1,401
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    I measured mine based off run time over a 12 hour period and an outside temperature the went from 45f to 40 back to 45. I came out to about 13600 btuh to maintain 72. That's assuming my boiler is running at 80%. 

    It is not running at 80% right now. Not even close. Lol