domestic hot water heater for hydronic heating?

[1 FMF]

http://www.bockwaterheaters.com/Portals/0/5-Installation_08_06.pdf
page 5 of pdf (39 on page).

Where permitted by code jurisdictions, a domestic water heater may be used as a heat source for hydronic radiant heating in a closed system, provided all generally accepted plumbing practices for closed-loop hydronic heating are used.

they also say:
- Bock water heaters operate at lower temperatures than boilers, using less fuel to heat potable and radiant water.
- Bock water heaters’ high BTU output makes them far more efficient for radiant heating than boilers.
- One unit heats both water and the home for greater economy
- A well-designed hydronic radiant system can reduce fuel use by as much as 40%.


this is for oil,
so far i'm calculating around 50,000 btuh of heat requirement for my home in winter, for 0 deg F outside and 70 inside. why not use a single oil fired hot water heater with a second loop to do the hydronic heat versus a traditional boiler?

 

[Donald]

That seems pretty low for BTU? How large a home.

What is the efficiency of a Bock water heater?

Have you considered a propane boiler, the new ones can modulate which oil cannot do.

Also the efficiency is of the boiler running. Not total. So if air can go through the boiler (when its off) and up the chimney (cooling off the boiler) then the real efficiency will be less than the efficiency they show you on a test.

 

[williestreet]

I am in the process of trying to source a new heat source for my hydronic system.
Currently have an oil boiler with a hot water coil for domestic hot water.

So far the best looking option for me is one of the new modulating Tank free heaters with a loop for hydronic heating and a second loop to a heat exchanger for the DHW.

I don't use a lot of hot water so running a boiler 7 months of the year just so I can have hot water makes no sense to me. I would see those to be similar idea. Keeping a very large tank of water hot all summer costs money. Probably more costly but I like the idea of instant hot water and no standby losses.

 

[Donald]

Originally Posted By: williestreet
I am in the process of trying to source a new heat source for my hydronic system.
Currently have an oil boiler with a hot water coil for domestic hot water.

So far the best looking option for me is one of the new modulating Tank free heaters with a loop for hydronic heating and a second loop to a heat exchanger for the DHW.

I don't use a lot of hot water so running a boiler 7 months of the year just so I can have hot water makes no sense to me. I would see those to be similar idea. Keeping a very large tank of water hot all summer costs money. Probably more costly but I like the idea of instant hot water and no standby losses.



The DHW coil was never a good solution. If you have a oil boiler the best solution for DHW is a tank with a coil that acts a zone to the boiler.

I assume the modulating tank free heater is gas?

 

[williestreet]

Yeah I never built the house. Bought it 7 years ago and every summer I say I am going to do something. Oil tank will need replacement in the next 2 years so starting to look right now.

Unfortunately no natural gas where I am so I am looking at propane or any other solution at this point.

There has to be a better solution than what I have now.

 

[1 FMF]

not sure if "radiant heat" is different than "hydronic heat".
i think by radiant they mean a run of pex tubing within a floor that would only get 100-120 degree water, and not old style baseboard heat.

the house interior is 34' x 24', two floors. current boiler is in basement that's door'd off from garage so it stays > 60 degrees in the winter. i've done a few online heat calculations and even when i try to over do it i'm still hitting only 50,0000 btuh of heat loss.
right now i have a 103k btuh oil boiler, 2 zone, and a standby bock 30 gal tank for domestic hot water. i ran out of oil and had to replace a circulator gasket couple weeks ago when it was 0 out. house got down to 55 deg. took boiler about an hour bringing up the hydronic system refilled with cold water to 180 degrees. then with both zones calling for heat the boiler would run for less than 10 minutes getting the water to 180'ish, shut off for 10-20 min while the house rose from 55 deg, then boiler kick back on for less than 10 min. this was first hand experience worst case scenario. so i'm fairly certain i'm at least 2x oversize for 2 zone heat at 103k btu, and i think the boiler currently has a smaller nozzle in it (according to service tag).