Boiler vs. water heater

Duncan

Either the boiler or the water heater will need a vent pipe run somewhere, hope that's not a problem.

There's two ways to get the amount of heat you need from air. You can deliver a large amount of air at a low temperature, or you can deliver a small amount of air at a high temperature.

Your existing duct work is the deciding factor. Normal sized ductwork wants higher air temperatures at lower air speeds, -but in your case maybe not- if it was *specially designed* for lower temperature (heat pump) range. More air at lower temps needs bigger ducts and bigger coils than with less air at hotter temps. It has to move a lot of air to take advantage of the lower temperatures, and also has to deliver it at a slow velocity, so it doesn't feel cold.

If a water heater is the source, like big ugh says, it may not get water temperature hot enough to practically use a hydro coil. Normal DHW (domestic hot water) temps are in the 120°F range, but hydro coils usually need AT LEAST 140°F to deliver useable heat. They typically like it even hotter than that. You'd almost certainly need to oversize the coil to deliver heat using a lower temperature water. No big deal.

You could crank up the DHW temperature and add a tempering valve to mix water temps down to avoid scalding when showering. Down side: That might increase wear and tear on the water heater, and the valve could fail dangerously. And all summer long when there's no call for heat, water sits in the fan coil - water you shower with.

With a boiler, you could add a heat exchanger and bronze pump to heat DHW in your existing tank. You could absolutely get higher fan coil temperatures for space heating, likely more efficiently than with a water heater, and the heating system water is not mixed with your DHW. Plus, boilers have a longer life expectancy. Down side: your water heater is already old, and the initial equipment investment would cost more than the water heater approach.

But your duct work needs to handle enough volume of whatever air temperature you eventually use.

Duncan

Mark_8

Boiler vs. water heater

I have two different solutions to a problem from two different professionals that I'd like more advice on. I have a oil-fired furnace for the 1st floor heat, a heat-pump for 2nd floor heat, and an electric hot water heater. The 2nd floor heat is not very efficient and is expensive to run. I wanted an answer to replace the 2nd floor heat and the electric hot water. Both solutions presented using the concept of a hydro-coil for the 2nd floor heat (optional for 1st floor). One person suggested installing a boiler and using the existing electric hot water tank as a storage tank. The boiler would provide water for home use and water for the hydro coil on the 2nd floor. The other person said you can't use that existing tank, and suggested an oil-fired water heater instead of a boiler to provide hot-water for home use and for hydro coil. Does anyone have any advice on which solution may be better, taking into consideration performace, long-life, and of course, money? Also, has anyone heard of Bock water heaters or Peerless cast iron boilers?

thanks in advance,
Mark

ta finnegan

Confused??

Hi:

There are often many possible solutions to heating and hot water system design. Ultimately the one that makes the most sense is the one that most closely resembles all your wishes for the performance and cost of this system.

Is cost the most important factor cost or comfort? Where do you live? Because I have found very few things on a "cost to operate" basis that can compare to geo-thermal.



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Gary Fereday

Time for a real design!

1. "Find a Contractor" who will start at the beginning! and calculate a heat loss for the place. 2. decide the tempertures of the water needed to shower, and heat the coil. I'd bet that two temps are needed. Shower temp is too cool for a coil and coil temperture is far to hot for the shower. That given, a Boiler makes sense. and your existing electric water heater CAN be used to store to store Shower water(especilly if is relatively new), and the Boiler can supply the higher temp needed for the coil.

Gary Fereday

Time for a real design!

1. "Find a Contractor" who will start at the beginning! and calculate a heat loss for the place. 2. decide the tempertures of the water needed to shower, and heat the coil. I'd bet that two temps are needed. Shower temp is too cool for a coil and coil temperture is far to hot for the shower. That given, a Boiler makes sense. and your existing electric water heater CAN be used to store to Shower water(especilly if is relatively new), and the Boiler can supply the higher temp needed for the coil.

Mark_8

One of them took a measurement of all of the rooms, would that be enough to do the heat loss calc? Your advice makes complete sense, which is helping me to determine which guy knows what he's doing. Thanks for your help.
Mark

Mark_8

Well, a healthy mix of cost and comfort would be nice. Ultimately, I'm willing to spend more for a more comfortable environment, provided it's a long-term, reliable solution. What do you mean by geo-thermal?

ta finnegan

Geo-thermal

Well if you are familiar with the refrigeration cycle, we use ambient air to cool the refrigerant in the system enough to condense, this is assisted with the fan in the condenser unit outside the house. When the heatpump switches to the heat mode it pulls heat fromt the outside to deliver it inside - simplistic, but it is the reverse of the cooling cycle.

The problem with existing R-22 and R-410A heat pump systems is that at 38-42 degrees outdoor ambient, the units fall back on resistive back up heat to heat the house.

Geo-thermal used the basal temperature of the soil, depending upon where you live is around 52 degrees year round. This means you never have to go to the resistive back up in order to heat the house.

I have had alot of success using and designing these systems even for radiant systems.

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Mark_8

Wow, I had no idea... Thanks so much for your time and advice.

Mark