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need new source for Hydronic Heat

Hey Folks,
We have a forced air hydronic heat system that uses our hot water heater as a source for both the heat exchanger and domestic hot water. While we do have some issues with the quality of the heat, I suspect that has more do with our house itself and is not quite what I need to tackle.

The real issue is that the Polaris water heater we have has been problematic since we've owned the house. Its costing us on average about $1000/year to repair and keep running. Of course it only conks out on the coldest days :eek: . We have also found it to be loud, inefficient (expensive) and in the winter we have a hard time taking showers longer than 7-10 minutes.

I've spent quite a bit of time having informal conversations with heating/cooling guys and they have all suggested replacing the Polaris with another high efficiency water heater, a Bradly-White for example. I have some concerns there, mostly about physical size. We have a very tight space with almost no room to spare.

I am interested in the viability of tankless systems. For instance, would a tankless system plus a small 25 gallon electric water heater (in a loop) suffice? What about two tankless systems- one for domestic and the other for the heat?

People have suggested that the tankless systems are still quite new and may end up being the repair nightmare that the Polaris has been. Others praise them.

Any thoughts or suggestions?

Thanks very much!

Re: need new source for Hydronic Heat


Many of the issues you mention have been covered in the "heat recommendations" post of 1/28/08, listed in the "Heating" section; there are many types of hydronic heating equipment discussed & the links (energy star) have a list of hundreds of energy-efficient hot water boilers and tankless systems.

Also check out "heatin with hot water" by Ralph Haskell on 1/22/08 in the "Heating" section; it lists the tankless/instant hot water heater systems/boilers that are just coming onto the market.

To read the post, scroll down to the bottom of the page and scroll thru the dept. types til you come to "Heating".

There are also heat loss calculations in the post that would allow you to determine the size heater you would need for your particular size house.

I think you should strongly consider installing a wall-hung boiler (in view of space restrictions) with a separate indirect water heater for the domestic hot water; this combination is unbeatable, because the IHWH doesn't burn any fuel, but gets its needed heat from the boiler water.

How well a unit produces heat and adequately provides the needed amount of space heat and/or DHW is based on the HEAT OUTPUT of the boiler/heater; this is measured in btu's/hour.

You can get a rough estimate of how much heat you will need to heat the house by taking the square footage of the house and multiplying by a number anywhere from 20 to 70 (20 = very tight house in mild climate; 70 = very drafty house in cold climate).

Thus if you house is 2000 sq.ft. X 30 (typical example) = 60,000 btu/hr; you would need a boiler or HWH that can output 60,000 btu/hr; & you would have to add another 20,000 btu/hr for the dhw.

Some of the HWH's like Polaris are being used these days for radiant heat, because they use lower temps in its distribution network of PEX plastic tubing & have a response time of hours.

However, the btu output of the system is still required to be 60,000 btu/hr to heat the building; in radiant, it's just spread over a longer time frame.

Recent trends in boiler manufacturing have been moving toward lighter, more compact condensing/variable output boiler units with combustion chambers made of stainless steel or aluminum, both of which can be hung on a wall in tight space situations, many of them no bigger than a large suitcase.

The TRADITIONAL boiler in past decades has always been made of cast iron & required a certain amount of floor space, as they weigh 600 lbs; these types of units still have a niche in the residential heating industry, because the design is tried & true, & they often cost much less than the newer, condensing/variable output models; gas-fired units proliferate on the market these days; oil-fired condensing units are now being introduced.

Could you list more info, such as the square footage of your house, your general location, level of insulation and if the unit is gas-fired or oil-fired; also for the hot tap water, how many people are in the house???

There are charts on the site below that allow you to estimate the "peak usage" of hot water in gallons (usually in the morning when everyone is preparing for work or school).

"Peak useage" and "recovery rate" would have a direct bearing on the size domestic hot water heater (DHWH) you would need; many households need a 30 gallon or 40 gallon indirect hwh for peak use times; the IHWH is a very economical way to obtain all the HW you need.

some of these units like Biasi B10 are designed to be installed in garages, where minimal heat is available.

Paloma Pak, Takagi, and Toyotomi, among others are marketing tankless boilers that also provide DHW; but I don't know enough about them to recommend or condemn them.


Re: need new source for Hydronic Heat
JacktheShack wrote:


Many of the issues you mention have been covered in the "heat recommendations" post of 1/28/08; there are many types of hydronic heating equipment discussed & the links (energy star) have a list of hundreds of energy-efficient hot water boilers and tankless systems; there are also heat loss calculations that would allow you to determine the size heater you would need for your particular house.

More to come.

Jack - thanks so much for the quick reply. I'll be sure to read the post you mentioned.

Re: need new source for Hydronic Heat

Jack -
After re-reading your very detailed post (thank you!) I have some comments and questions.

First, to address your questions:

The house is a 1940's A-Frame Cape Cod style brick house. Its a fairly typical older here in Richmond Virginia. The walls are totally uninsulated - something we should have addressed during our remodel but did not. We have completely insulated under the first floor (via crawlspace) and blew quite a bit of cellulose into the attic above the 2nd floor. We have also added storm windows.

Typically, its just my wife and I here, although we do have company from time to time. It is quite rare for both showers to be running at once, however our shower in our master bath does has two body jets in addition to the shower head.

We are serviced by natural gas, and our Polaris is a natural gas unit.

I have three major goals:
1) reliability - I'm tired of having to have the polaris serviced all the time.
2) Conserve space- our utility room is very small and dose double duty as a laundry space. There is not much room to move to a larger hot water tank, for instance.
3) energy efficiency - the polaris is nowhere near as efficient as it claims (and maybe nothing will be in this house) but it costs us a small fortune in the winter months to heat the house.

I might add a minor concern about safety - we recently had a carbon monoxide scare that would have ended poorly if we had not left the house when we did.

That may give some insight into my interest in a tankless system. I like the idea of a wall mount unit that does not take a lot of space and operates only when needed.

That said, I like your idea about a wall hung unit and a indirect tank. I am not sure I fully understand that system though... is that using a furnace/boiler rather than tankless water heater?

What about using a tankless water heater? A few options I've been researching include:

  • *Two tankless water heaters - one for the hydronic heat and one for domestic HW. I'd probably use two different sized models- with a larger one for the heat.
  • *a tankless hot water heater that feeds through a small electric HWH - the idea being that the water going into the electric unit would already be hot...then draw from that for the heating system and return back through the tankless.... giving the system a "buffer"
  • *One large tankless HWH with a loop for the heating system

Are any of those options viable?

Finally, you mentioned calculations. Based on the rough one you mentioned, we have about 1700 sq feet and I used a multiplier of 50 then added 20,000 for the domestic HW and came to 71,000 (which is exactly what one contractor quoted). I was not able to find the peak usage calculations on the link you posted.

Re: need new source for Hydronic Heat


Yes, some of the options you mentioned regarding tankless/instant hot water systems are certainly worth a consideration.

I get the feeling reading your post that you still need to talk to more HVAC people in the Richmond area.

As time goes by, I feel sure you will get a clear picture of what's best for your situation.

I frankly don't trust some of the tankless/instant HW systems yet, because they don't have a long track record; many of the heating engineers don't like them to heat a house, probably because the technology on them is still developing.

Also, I'm based in New England.

Up here we have a lot of oil-fired and gas-fired boilers with hydronic radiators and baseboard designed for very cold winters.

so I tend to favor such systems.

But for Richmond, the HVAC situation is different; your concern is perhaps as much for an AC system for the summer heat, combined with a heating system that will keep the house warm at low cost during moderate winters.

The local heating installers clearly would know a lot more than I about what's best for your area.

This might include heat pumps, mini-split ductless AC units that double as a heat pump, etc.; systems that would probably be inappropriate for New England might be fine for Virginia.

I have a lot of confidence recommending the new lighter weight wall-hung condensing gas-fired stainless steel boilers by Triangle Tube Prestige, Peerless Pinnacle, Buderus GB142, Burnham CHG/FCM, Dunkirk Quantum, Biasi Riva, & Viessmann Vitodens.

These are from some of the top heating mfgs in the U.S. & Europe & have an excellent track record.

But if the local heating equipment wholesalers and installers don't carry such equipment, or are unfamiliar with them, then this has to be taken into consideration.

Definitely try to get some insulation blown into the exterior walls if you can (more difficult sometimes with brick).

You should do the free slant fin HLC to get an accurate idea of what the heat loss is; the slant fin HLC is comprehensive & takes about an hour, but it is very accurate.

I mispoke when I mentioned a chart on the site regarding the "peak use" of the DHW.

The procedure is to add up the hot water usage the family experiences during a peak period, such as the "morning rush", using the figures given for how many gallons are used for showers, washing, dishwayer, etc., then select a DHW system that can deliver that amount of HW.

This is where many instant/tankless HW heaters fall down.

They produce a few gallons & then go lukewarm.

This is also a problem with boilers that have what's know as a DOMESTIC HW COIL (a 3/4" copper coil ~ 10' inside the boiler) to heat the DHW; it's good for a few gallons of HW while you're in the shower, then the water goes lukewarm.

That's why a 30-40 gal. INDIRECT HWH that stands side by side of the boiler is recommended.

They're only 2' wide & 6' high (Triangle Tube recommended), & can even be placed in an upstairs closet if no room exists in the utility room.


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