ISTA BTU monitor for heating cost apportionment BTU Monitoring for Heating Cost Apportionment

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BTU monitoring for heating cost apportionment: this article describes BTU monitoring equipment & other means of heating cost apportionment across multiple rental apartments or other multiple dwellings when served by a common heating system.

We describe several approaches used to assign a share of heating cost to individual building occupants or tenants, ranging from square footage to heat-on-timers to much more accurate BTU usage monitoring equipment that tracks actual heating energy used by each heating zone or occupied area.

Shown at page top is a 1980's vintage Ista (now Istec Energy Systems) BTU monitoring device.[5]

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Heating Cost Apportionment Problems & Solutions for Rental Apartments in the U.S. & Europe

ISTA BTU monitor for heating cost apportionment

How can we best assign a fair share of heating costs to individual apartments, tenants, rental or other units in a multi-occupant building?

Here we describe methods to assign a fair share of heating costs to building occupants according to their actual demand for heat.

Separately at at AIR LEAK DETECTION TOOLS and also at BASEMENT HEAT LOSS DETECTION we discuss the problem of heat loss and uneven heating particularly in two-story multi-family homes with an upstairs and downstairs tenant and a single heating system with a single thermostat located on the first floor.

This problem is related to fair assignment of heating costs. The upstairs tenants are too hot and the downstairs tenants are too cold.

The illustration (left) shows an Ista BTU monitor design from 1985, one of several heating cost apportionment devices discussed along with their modern (and much less costly) counterparts shown in the article below. Ista is now Istec Energy Systems.

In Europe BTU monitoring and accurate heating cost apportionment among tenants is required by law, but this is not the case in the U.S. nor Canada. Nevertheless building owners are increasingly faced with tenants who want to be sure that individuals are only being taxed to pay their fair share of building heating costs.

Energy Use Monitoring: Hot Water Heat, Steam Heat & Warm Air Heat

Hot water - hydronic heat BTU monitoring & energy consumption measurement: most of the energy use or BTU use monitoring devices we have observed are designed to measure fluid temperature and fluid flow rate (presumably hot water moving in hydronic heating system pipes through circuilators, possibly zone valve, and radiators or heating baseboards or radiant heat tubiing).

Measuring both flow rate (lpm or gpm) and temperature allows a reasonably accurate measure of the rate at which BTUs are being requested by an individual heating zone, area, apartment or tenant.

Warm air heat use by individual zones could be measured by a similar approach but it's more difficult to do so with precision. More likely a building manager will seek to simply measure heat-on demand by individual zone, approximating BTU consumption by noting the duration of calls for heat at individual thermostats or individual zone dampers (in the open position).

Slowing warm air movement between floors by insulation and sealing may be helpful, but an optimum solution includes separate heating zones and zone controls, or even separate heating systems entirely, permitting accurate heating cost apportionment among the tenants.

Steam heat use by individual zones or tenants may be measurable by indusrtrial process equipment, but as you'll read in our specific device notes below, costs for this approach can be significant, in thousands of dollars per zone. A steam heat monitoring device from GE Panametrics (GE Panaflow MV80) retails at prices starting around $2000. U.S.

Four Approaches to Heating Cost Apportionment among rental units

BTU Monitoring Equipment may be required by law for rental units in Europe where a common heating system is used to heat (or A/C to cool) multiple apartments in a single building but those devices are seeing increased interest in the U.S. as well.

1. Simple Heating Cost Apportionment by Floor or Unit Area

Heating cost apportionment by square feet or by floor is often used in two family homes in the U.S. The landlord simply divides the heating bill in two if the two rental units occupy about the same square footage, or s/he may apportion heating costs by actual square footage of the home. The inaccuracies of this approach can be significant. For example, a second floor apartment is receiving some heat from the floor below; or one tenant may keep their heating thermostat set lower than another.

2. Heating Cost Assignment using Zone Valve Timers

Heating zone-on timers, a "budget" approach that does not accurately measure actual BTU consumption has been used by some of our readers and clients. The appeal of this less accurate approach is that the installation and equipment to simply keep track of the length of time that a heating zone or heating thermostat is calling for heat is often less costly and simpler to install than true BTU monitoring equipment.

A zone valve is a small low-voltage electric motor that is operated by a room thermostat corresponding to that individual heating zone or area - a loop of heating pipe routed through one or more rooms. The thermostat calls for heat, the zone valve opens, an end switch turns on a circulator (or boiler depending on installation details). When the thermostat is satisfied it stops calling for heat which in turn closes the zone valve.

Accuracy of heating zone timers for BTU monitoring

Because the operation of the zone valve is by a simple low-voltage electrical circuit, it's not difficult to construct a timer that monitors the "heat on" elapsed time for that zone. But without measuring temperature and flow, the simple "heat on" measure is inaccurate and crude compared with true BTU monitoring.

For example just consider two different heating zones both of which operated for an hour.

It will be apparent that simply measuring heat-on without considering at least the square footage is close to meaningless in assigning heating costs. Even measuring square footage does not accoiunt for differences in heat loss between two areas. This approach is not approved for European rental units.

3. Fuel Demand Meters Monitor Fuel Consumption not BTU Consumption

Fuel demand meters: are used where multiple individual heating appliances are installed and the building owner/manager wants to monitor fuel consumption by individual heating appliance. Example - Johynson fuel demand meter.

4. BTU Usage or BTU Consumption Measurement Using Monitoring Devices

Badger 380 BTU MeterActual BTU usage, a more precise approach, monitors are typically devices that measure temperature and flow rates of hot water in individual heating zones. This approach is the most accurate means of determining actual energy consumption or heat usage in differnt building heating zones, occupancies or by different tenants.

BTU meters available in North America have come a long way since we first reported on this topic back in 1985 (illustration at page top).

Currently several manufacturers produce a range of BTU monitoring equipment suitable for mounting on hydronic heating system piping and capable of giving BTU consumption measurement data accurate enough to satisfy both E.U. requirements and those in other countries.

Shown at left is a contemporary BTU monitoring device, the GF Signet 8900 Multi-Parameter controller produced by Georg Fischer. This single device, equipped with multiple sensors, can monitor multiple channels simultaneously.

When we first looked at this equipment back in 1985 there was a bit of sticker-shock as quite a few devices were clearly designed for industrial applications, not residential or apartment use.

For example in 1985 a Series 450 Energy BTU flowmeter by Controlotron cost roughly $7,400. per heating zone (at that time). Happily engineering progress including the use of VLSI circuitry has led to new, less costly devices from these and other manufacturers as we illustrate below. The Badger Model 380 BTU meter sdetailed in the text below retails at prices starting at $560.U.S.

For measuring & monitoring electrical energy consumption

Sources of BTU Monitoring Equipment

Badger 380 BTU Meter

Ista_Model5201 BTU Meter



Veris FST flow meter / BTU meter - Veris Industries

Accuracy of BTU Monitoring Equipment

The accuracy of energy monitoring by counting BTU consumption may be affected by the methodology used. More costly to construct and install, actual physical flow monitoring that uses a paddle or wheel sensor mounted in the heating water flow path can provide a very accurate measurement of flow-rate of water in liters or gallons per minute. That data combined with constant monitoring of water temperature can give accurate results. But having to place moving parts in the flow path means expensive equipment and risk of technical problems from clogging, debris &c.

Potentially similarly accurate BTU monitoring may be achieved by ultrasonic devices that clamp on to a pipe to measure flow rate of fluid inside the pipe. But these methods two can produce results that vary in precision depending on just what is in the flowing water (or other liquid) such as entrained air or debris.

Watch out: be sure to discuss your BTU monitoring application with the manufacturer. Some of energy use monitoring devices, particularly those relying on ultrasonic sensors rather than physical flow measurement by impeller, are sensitive to air or contaminants in the fluid flowing through the heating distribution piping. For example, Veris notes: "ommercial and industrial installations involving clean liquids or liquids containing small amounts of suspended solids or aeration".

Reader Question: Is there a measuring instrument that can be put on the zone valves to measure the amount of heat used by each apartment ?

I found your site on line. I have a 4 unit house that I live in. Each apartment has it's own heating zone. Is there a measuring instrument that can be put on the zone valves to measure the amount of useage each apartment uses? I would greatly appreciate a response. H.R. 2/20/2012


There are heat-usage monitoring devices used (e.g. throughout Europe) that accurately track how much heat is used by each heating zone or apartment by measuring BTU consumption. What's needed to be even close to accurate is heating water flow rate (lpm or gpm), flow time, and temperature.

In the U.S. where heating cost apportionment is not required by law, some folks make a crude stab at apportioning costs by installing a simple (less expensive) timer that monitors how much of the time a particular zone is calling for heat. There are obvious reasons that a simple approach may be unfair, such as differences insulation, heat distribution, rates of heat loss, in different areas.

We discuss the alternative means of measuring or guessing at how to apportion building heating cost among its tenants in the article above.


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