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Best whole house solution - hydronic heat and dhw

dcvict Member Posts: 2
Hi guys, would love to hear your ideas on best replacement system(s) for my old oversized boiler and 80gal hot water heater. Both gas-fired and chimney vented. Calculated heatloss for house is 120K, has 4.5 bathrooms. Radiators are old cast iron columns and baseray units. Is an old rowhouse in Washington DC.

Have had a number of pros through the house bidding a/c system, but they all had very different comments on the boiler and DHW, so not sure who to believe. They did have two general biases though:
1) A premium grade combi boiler like Rinnai Q Premier could do whole house heat and dhw, no problem
2) This old equipment is just fine, maybe inefficient, but not worth cost of replacing 'til it breaks. Maybe turn the temp down on boiler, try to modulate it. Combi boilers are junk, impossible to service, etc.

To make things complicated, we're removing radiators from some rooms, replacing some with new panels and going with heatpumps and hydronic coils in a/c system to be safe. Also, aim to replace bathroom radiators with hydronic floor systems when get around to renovating the bathrooms.

So many questions, but guess main ones are:
1) Definitely is (or is not) smarter to keep as many radiators as possible vs. relying 100% on forced air hydronic coils?
2) Can any combi boiler or tankless hwh actually handle dhw for 4.5 bath house? Basement may become a rental unit and lots of women in the house, so absolutely need to deliver 3-4 simultaneous hot water draws. Was very excited by option to save so much floor space in utility/laundry room, but not if hot water becomes a problem.
3) Do the old cast iron radiators work properly with lower temp water and new generation efficient boilers?
4) Do contemporary panel radiators and hydronic floor and forced air coils work properly with high temp water?
5) New style 'direct vent' units can't be vented up the chimney stack? Have some exterior wall venting options, but not easy. How far below, above or laterally removed from a neighboring doorway or window must these direct vents be placed? How long can the total vent run be?
6) I see Triangle Tube and Buderus mentioned often as best boilers. Is this a real long term consideration or any major boiler manufacturer is just fine?

Sorry to ask so many questions at once, but it all seems interrelated, to me. Please feel free to weigh in on any or all of these issues. Thanks!


  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    I'd try and keep as many radiators as possible, as they hold their heat longer than a forced air solution. I'd also be using a Viessmann boiler (the new Vitocrossal CU3A) that condenses and doesn't require hydraulic separation. The boiler can be vented through the existing chimney with a flexible PPE liner. All boilers are not the same. The older radiators can be used at lower temps, if sized correctly. The Viessmann Vitocell 300 DHW tanks will outlast other tanks with very fast recovery. Combi boilers will not provide recovery rates acceptable for large DHW drawdowns.
    Try contacting Dan Foley at Foley Mechanical in Arlington. He has extensive experience in the DC area and his craftsmanship is 4 stars. http://www.foleymechanical.com/
  • njtommy
    njtommy Member Posts: 1,105
    If your rads are in good shape keep them. You can run a high efficiency boiler with your current rads. It's just a matter of what your max boiler supply temp will be for design day. Your old rads my be over sized and can run at say 160f on a 0 degree day, but on a 50 degree day you could run 120f supply water.
    This is where an out door reset control comes in handy it will also keep your efficiency up with lower return water temps.

    Combi boilers are great and serve there purpose. It may not be right for your application due to the amount of DHW you will need to run 4 showers or tubs at the same time. Even most tankless hot water heaters will not handle this load with out running 2-3 of them together.

    Hydronic coils, panel rads, and radiant flooring will work together.

    Typically speaking radiant flooring runs at a lower temp. Which is what you want for a high efficiency boiler.

    Hydroair coils and panel rads work great at high or low supply water temps. They just need to be sized accordingly.
  • Rich_49
    Rich_49 Member Posts: 2,766
    Keep as much cast iron as you can , piping to hydro fan coils as a redundancy measure is acceptable .

    There is not a tankless unit that has the capability you describe . Maybe a few cascaded .

    What heat pumps are you using ? Air to water HPs top out at around 130* F water temps . There is a new unit out that is claiming makes hotter (150*) . Cannot think of whose unit that is .

    Paul had a very good idea . Foley Mechanical is unsurpassed and you don't ever have to wonder whether what he says is correct . His guys are top shelf also , very talented men .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Steamhead
    Steamhead Member Posts: 16,823
    I'll add my recommendation for keeping your existing radiators and having Foley do the work. You can't go wrong with either.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • njtommy
    njtommy Member Posts: 1,105
    I love my hydroair set up over my straight heat pump. But I can honestly say I can't wait to get on to my next stage of my heating project of radiant floor and panel rads.