Hot Water questions

camiarrobino

Hello, I recently moved into a new house. I have FHW heat via radiators, from an oil-fired Weil-Mclain boiler. It's about 8 years old with AFUE of 85. From what I understand, the boiler is a combo boiler and also provides the hot water for the house. There is no storage tank nor is there a dedicated hot water tank. I'm trying to understand why the boiler needs to run all the time to keep the water hot, even when the thermostat isn't calling for heat and no hot water is being used at any fixtures. This is a single-level cape-style house with 1 bathroom and 1 heating zone. I've been told that I could cut back on oil usage significantly with an indirect hot water system, using a tank attached to the boiler. The price however seems steep. Would adding an electric water heater tank have the same effect w/r/t the boiler not needing to heat water 24/7? Between not being home that much and not minding the house chilly, I don't go through much oil for heat, and I'm trying to find the most cost effective solution to prevent the boiler from having to run so often

Solid_Fuel_Man

What you have is called a tankless coil. I like to call them chimney heaters. 

You have several options. 

1. Install an indirect tank, uses boiler water to heat domestic water through a coil in a tank.

2. Install a stand alone water heater. This can be oil, gas, or electric.....or heat pump.

3. On demand water heater, this can be gas, or electric. 

Of these options either an indirect or a heat pump water heater would be likely the best options. Indirect water heaters can still use a bit of oil, although significantly less than the chimney heater you have now. Heat pump water heaters depend on your electric rate and if there are rebates etc. They steal heat and humidity for the space they are in. Sometimes this is a great thing, and other times it isn't. 

mattmia2

You must have a tankless coil. It is a coil that sits in the hot water in the boiler and domestic water runs through it and us heated by the boiler water. The boiler has to be hot whenever you want hot water, it can't heat quickly enough to make hot water on demand if the boiler is cold. There is an aquastat, usually part of the heating control, that keeps the boiler hot all the time to make hot water.

An indirect is the least cost to operate option depending on your relative cost of oil and electricity but the up front cost is a lot more. An electric water heater may be the lower overall cost because of the lower up front cost. It is also possible to pipe the tankless coil to heat the electric water heater when the boiler is operating.

mattmia2

130-140 is enough to prevent the boiler from suffering sustained condensation. In most applications you will need more than that to produce enough hot water with the tankless coil.

GEO80

Seems 132 or more minimal setting as remembering particular excellent s.steel condensing boiler companies usually state to get the fluid back to the boiler below 132 to ensure "high efficiency condensing". - which is not wanted in your boiler = perhaps always set at a real 132 or warmer.

Another option if oil is used above ~est, $1600 annually, and better if your costs are greater.. there are now several manufacturers having heatpumps for A/Conditioning as well as recovering summertime heat back to your , then ~ 80 gal. or two standard 40's or 50's gallon HW tanks wile you have more central cooling/ a little ducting for a small system, too, geothermal complete as 4-part synergistic-ally:

Hot Water on demand by temperature control
Hot water Heat recovery in A/C
hot water BY GEOTHERMAL to boiler piped zones until oil must take over the loads
if some of the ducted- air is also not producing enough heat in heating mode
and
regular A/Cooling.

There are Air-Source Heat Pumps with heat recovery as well - depends on how well layouts to costs and ReturnsOnInvestments seem realistic at your awaiting 6, 7, 8 years returns. But deduct indirect and other Hot Water tank costs on the table, to consider.

One such system , 2005, 3-staged dual compressor, kept the home warm enough, simply, that no supplemental fuel is ever used : Harrisburg PA 2300 sq ft , 2 people live comfortably, only 2020 went above all electric all house bill previously under @ $ 97.00 monthly (all of the home and HW and A/C) ducting with ~ 60% radiant. Again with dedicated heat pump air and domestic hot water on demand by temperature control and heat-reclaimed in A/C mode.

-only worked with all 14 successful, still same compressors, since 2004.

GEO80

Key was also oversized unit heat exchanges, oversized ground loops, or quality well source ( iron under 1/2PartsPerMillion ). Another metered ex-oil, electricity metered, under $400, annually, all Heat A/C, -recovered HW heating-reclaimed, and on-call Hot Water... customer records in a ledger !
Another 5500 sqft with 3 staging GeoThermal/ HW-heat-reclaim and radiant heat produced- family of 6, zone 6 Northern Ohio area, is nearing $300/monthly all electric total home. 2008 then after purchase-credits (check with your accountant) estimated just about five year (19% ROI/annually ( -compounds as cost of living keeps rising - so much more at present! ) on their 7-ton compressors (3+4T).

GEO80

ok that is 3200 sqft w/ just under $400. annual A/C, HW -Demand/ recovered, and Heat, on decent well water.